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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
An authoritative discussion of safety considerations for professionals and operators working with or around nitrogen and other inert gases
In Hazards of Nitrogen and Other Inert Gases: How They Can Be Safely Managed, experienced refinery supervisor and manager M. Darryl Yoes delivers a thorough discussion of the use of nitrogen and other inert gases in the refining industry and other industries where they are commonly used. The author includes a complete exploration of the hazards of working with and around nitrogen, as well as case studies of incidents involving nitrogen in both gas and cryogenic forms, and other inert gases, including carbon dioxide, argon, and neon.
Yoes walks readers through the most critical safety aspects of working with asphyxiants such as inert confined space entry and discusses how to avoid and prevent catastrophic incidents. The book offers self-quizzes, essential terms, key workflows, and checklists for routine practice.
Readers will also find:
- A thorough background on nitrogen use and the hazards that flow from working with it
- Comprehensive explorations of incidents involving asphyxiation, hypoxia, and cold burns resulting from nitrogen (gas and liquid form) and other inert gases
- Practical discussions of the prevention of catastrophic incidents involving inert gases
- Additional discussions of other inert gases, including carbon dioxide and helium
Perfect for all operations personnel who work with or around asphyxiants, including petroleum refining and petrochemical plant operators, line supervisors, and process and mechanical engineers, this book will also benefit new operators and advanced students learning about or working with nitrogen and other inert gases.
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Veröffentlichungsjahr: 2025
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Table of Contents
Cover
Table of Contents
Title Page
Copyright
Preface
Note to the Reader
About the Author
Chapter 1: The Properties, Uses, and Safety Hazards of Nitrogen
End of Chapter 1 Review Quiz
Additional References
Chapter 2: The Properties, Uses, and Safety Hazards of Other Inert Gases
2.1 Argon (Ar)
2.2 Carbon Dioxide (CO
2
)
2.3 Carbon Monoxide (CO)
2.4 Helium (He) (Overview)
2.5 Neon (Ne)
2.6 Krypton (Kr)
2.7 Xenon (Xe)
2.8 Light Hydrocarbons
End of Chapter 2 Review Quiz
Additional References
Chapter 3: The Effects of Nitrogen and Other Asphyxiants on the Body (Oxygen Deprivation)
End of Chapter 3 Review Quiz
Reference
Additional References
Chapter 4: Protection for Personnel Against Inert Gas Asphyxiation and/or Cold Burns
4.1 Adequate Warning Signs and Barricades
4.2 Personnel Gas Monitors and Continuous Gas Quality Monitoring and Alarms
4.3 Use of Self-Contained Breathing Apparatus
4.4 The Documented Work Permit (The Authorization for Specified Work to Begin Issued by an Authorized and Designated Individual)
4.5 The Union Carbide Nitrogen Asphyxiation Incident – Date of Incident 27 March 1998 Investigated by the Chemical Safety and Hazard Investigation Board Final Report Issued 23 February 1999 (Report Number 98-05-I-LA)
4.6 Confined Space Entry
4.7 Protection Against Supercold Liquids such as Liquid Nitrogen
End of Chapter 4 Review Quiz
Additional References
Safety Suppliers (Reference only)
Chapter 5: Confined Space Entry – The Occupational Safety and Health Administration Standard (29 CFR 1910.146) and Some Key OSHA ‘Letters of Interpretations’
5.1 The US OSHA Confined Space Regulation ‘29 CFR 1910.146 – Permit Required Confined Spaces’
5.2 Confined Space Entry Letters of Interpretation by OSHA (Standard 29 CFR 1910.146)
End of Chapter 5 Review Quiz
Additional References
Chapter 6: The Hazard of Contaminated Breathing Air and How It Can Kill
6.1 The Use of Utility Air or Instrument Air as Breathing Air Should Not Be Permitted
6.2 Fatalities Due to Using Blended or Manufactured Breathing Air
6.3 Requirements for Breathing Air to Ensure Quality (from the OHSA Technical Manual on Respiratory Protection)
6.4 Summary of OSHA Requirements for Breathing Air Quality
6.5 Notes from the Regulation and the OSHA Technical Manual on Respiratory Protection
6.6 Other Specific Requirements
End of Chapter 6 Review Quiz
Additional References
Suppliers of Safety Equipment:
Chapter 7: Most Frequent Causes of Nitrogen Asphyxiation and How to Address Them
End of Chapter 7 Review Quiz
Additional Resources
Chapter 8: More on Safe Utility Connections
End of Chapter 8 Review Quiz
Additional References
Chapter 9: The Hazards of Inert Entry and an Overview of the Process (Includes Case Studies of What Has Happened)
9.1 Background
9.2 Specialized Inert Entry Procedures
9.3 Inert Entry Planning
9.4 The Job Safety Analysis
9.5 Acceptable Inert Atmosphere
9.6 Inert Gas Supply and Quality
9.7 Breathing Air System
9.8 Assuring Breathing Air Quality
9.9 The Contractor Selection Process
9.10 Life Support Equipment
9.11 Confined Space and Inert Entry Rescue Plan
9.12 Video Surveillance Equipment/Rescue Equipment
9.13 Reactor Preparation for Entry
9.14 Caution
9.15 Catalyst Crusting (Another Caution)
End of Chapter 9 Review Quiz
Additional Resources
Chapter 10: Carbon Capture, Use, and Storage
10.1 How is the Industry Responding to This Increase in Carbon Dioxide?
10.2 Safety Aspects of Carbon Capture, Use, and Storage (CCUS)
Abbreviations
End of Chapter 10 Review Quiz
Additional Resources
Carbon Capture – Opposing Views
Chapter 11: Nitrogen Asphyxiation Case Studies, and Asphyxiation by Other Inert Gases
11.1 What Has Happened / What Can Happen Incident Case Study Number 1 – Nitrogen Asphyxiation
Key Lessons Learnt
11.2 What Has Happened / What Can Happen Incident Case Study Number 2 – Nitrogen Asphyxiation
Key Lessons Learnt
11.3 What Has Happened / What Can Happen Incident Case Study Number 3 – Argon Asphyxiation
11.4 What Has Happened / What Can Happen Incident Case Study Number 4 – Argon Asphyxiation
Additional Resources (in Singapore)
Additional International Resources
Additional Resources (in the United States)
11.5 What Has Happened / What Can Happen Incident Case Study Number 5 – Carbon Dioxide Asphyxiation
11.6 What Has Happened / What Can Happen Incident Case Study Number 6 – Low Oxygen Content (Asphyxiation)
11.7 What Has Happened / What Can Happen Incident Case Study Number 7 – Employee Dies due to Asphyxiation from Oxygen Displacement
11.8 What Has Happened / What Can Happen Incident Case Study Number 8 – An Explosion Occurred While Unloading Liquid Nitrogen at an Ice Cream Facility (10 Injured)
11.9 What Has Happened / What Can Happen Incident Case Study Number 9 – Fatality of Welder in Confined Space Welding in the Presence of Argon
11.10 What Has Happened / What Can Happen Incident Case Study Number 10 – A Summary of Incidents Involving ‘Would-be Rescuers’
End of Chapter 11 Review Quiz
Additional References
Chapter 12: Summary of Additional Actions to Help Prevent Asphyxiation Incidents at Our Facilities
End of Chapter 12 Review Quiz
Additional References
Chapter 13: Additional Discussion of Liquid Nitrogen Use in Ice Cream Shops
Injuries or incidents related to liquid nitrogen use in ice cream shops:
End of Chapter 13 Review Quiz
Additional Resources
End of Book Quiz
Appendix 1: Answers to the End of Chapter Quizzes
End of Chapter 1 Review Quiz
End of Chapter 2 Review Quiz
End of Chapter 3 Review Quiz
End of Chapter 4 Review Quiz
End of Chapter 5 Review Quiz
End of Chapter 6 Review Quiz
End of Chapter 7 Review Quiz
End of Chapter 8 Review Quiz
End of Chapter 9 Review Quiz
End of Chapter 10 Review Quiz
End of Chapter 11 Review Quiz
End of Chapter 12 Review Quiz
End of Chapter 13 Review Quiz
Appendix 2: Answers to the End of Book Quiz
End of Book Quiz (With Answers)
Appendix 3: Documented Incidents Involving Nitrogen Resulting in Fatalities or Serious Injury
Index
End User License Agreement
List of Illustrations
Chapter 1
Figure 1.1 National Library of Medicine, National Center for Biotechnology Info...
Figure 1.2 Location of the nitrogen-induced fatality.
Chapter 4
Figure 4.1 Example of a nitrogen inert gas purge warning sign that should be pl...
Figure 4.2 Confined space entry sign, which had been placed at the access point...
Figure 4.3 An image of the sign that replaced the ‘Danger – Confined Space – Do...
Figure 4.4 A photograph of a personal H
2
S monitor.
Figure 4.5 Basic four-gas monitor/USA NIST calibration.
Figure 4.6 Example of a self-contained breathing apparatus (SCBA) with a full-f...
Figure 4.7 Union Carbide Plant; one end of the 48-inch diameter pipe, which was...
Figure 4.8 Illustration of warning signs near oxygen-deficient atmosphere with ...
Figure 4.9 Illustration of oxygen-deficient atmosphere. Never place your head o...
Figure 4.10 Personal protective equipment, including an apron, gloves, gaiters a...
Chapter 6
Figure 6.1 Image of a nitrogen utility quick-connect fitting modified to connec...
Chapter 7
Figure 7.1 Photo of typical facility utility connections.
Figure 7.2 Close-up of the three unique quick connections. The fourth unique qu...
Chapter 8
Figure 8.1 Example of a plant utility station.
Figure 8.2 Example of a common pipeline connected to process equipment with two...
Figure 8.3 a and b Two examples of ‘cheater’ connections used to cross-connect two diff...
Figure 8.4 Whip check, designed to prevent a flailing hose in the event of a co...
Chapter 9
Figure 9.1 Example of a breathing air control panel where breathing air is cont...
Figure 9.2 Photograph of two catalyst technicians in their working suits equipp...
Figure 9.3 Photograph of two catalyst technicians in their working suits equipp...
Figure 9.4 Catalyst technician entering a permit required space with inert entr...
Figure 9.5 Example of a cable reel used for the unbiblical air supply hoses and...
Figure 9.6 Catalyst technician fully outfitted and prepared for inert entry. Pl...
Figure 9.7 Catalyst technician fully outfitted and prepared for inert entry. Pl...
Chapter 11
Figure 11.1 Immersion freezer at the Foundation Food Group.
Figure 11.2 The immersion freezer bubbler tube (level control device). Notice th...
Figure 11.3 The Delaware City Refinery hydrocracker reactor top flange.
Figure 11.4 Close-up image of the safety sign placed at the reactor vessel’s ent...
Figure 11.5 Roll of duct tape lying on the hydrocracker reactor distributor tray...
Figure 11.6 Roll of wire used by contractor in attempt to remove the duct tape f...
Figure 11.7 An image of the piping welding site where a welder was asphyxiated b...
Figure 11.8 a and b The Meriwether Compressor Station, serving northern Montana.
List of Tables
Chapter 2
Table 2.1 Overview of carbon dioxide health effects on the human body.
Chapter 3
Table 3.1 The physiological effects of less oxygen (oxygen deprivation).
Chapter 6
Table 6.1 OSHA 1910.134 breathing air quality.
Chapter 11
Table 11.1 Review of Appendix: numbers of documented incidents involving nitrog...
Guide
Cover
Table of Contents
Title Page
Copyright
Preface
Note to the Reader
About the Author
Begin Reading
End of Book Quiz
Appendix 1 Answers to the End of Chapter Quizzes
Appendix 2 Answers to the End of Book Quiz
Appendix 3 Documented Incidents Involving Nitrogen Resulting in Fatalities or Serious Injury
Index
End User License Agreement
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Hazards of Nitrogen and Other Inert Gases
How They Can be Safely Managed
M. Darryl Yoes
Safety Consulting International, LLC
Jackson, LA, USA
Copyright © 2025 by John Wiley & Sons Inc. All rights reserved, including rights for text and data mining and training of artificial intelligence technologies or similar technologies.
Published by John Wiley & Sons, Inc., Hoboken, New Jersey.
Published simultaneously in Canada.
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Cover Images: © zorazhuang/Getty Images, US Chemical Safety and Hazard Investigation Board (CSB)
Preface
My wife and I recently took a short vacation to South Florida, visiting the Everglades and Key West. It was a great chance to get away for a few days and enjoy the beautiful scenery and sun. While passing through Key Largo, we stopped briefly at an ice cream shop, and to my surprise, I discovered ‘Nitrogenated Ice Cream.’ For those familiar with it, it will be no surprise that the shop had a ‘selfie station’ where customers could snap a picture of themselves directly in front of their liquid nitrogen storage tank. An image of the liquid nitrogen tank located inside the ice cream parlour is on the next page. You will note that it is labelled as a ‘selfie station’ where customers are invited to take photographs of themselves and others.
I was painfully aware of the recent investigation report released by the US Chemical Safety Board of six fatalities that had occurred at the Foundation Food Group (FFG) facility in Gainesville, Georgia, due to asphyxiation by liquid nitrogen. This incident occurred on 28 January 2021, when the liquid nitrogen level rose and overflowed in an immersion freezer, releasing the liquid into a confined space, the room where the freezer was located.
This book describes this incident in more detail as a case study. The six deaths were due to oxygen deprivation, the most significant hazard associated with releasing nitrogen into confined areas. Two of these deaths occurred due to the release of liquid nitrogen. The other four deaths occurred when other employees attempted to investigate the release or rescue of the first two employees. In my experience, this is very common in nitrogen incidents due to the human urge to help others in trouble. Rarely is only one person killed by nitrogen. Frequently, another person, and sometimes several others, also die while attempting to render aid to those who are already down. This is precisely what happened at the Foundation Food Group facility.
A similar incident occurred in April 2013 at a beer brewery in Mexico where seven workers, including three company employees, were killed in a confined space entry accident while cleaning a beer fermentation tank. It was believed this incident occurred due to inert gas, either carbon dioxide or nitrogen, and all three of the employees died while attempting to rescue the four downed contractor employees.
So, while at the ice cream shop, I attempted to understand more about using liquid nitrogen in ‘nitrogenated ice cream.’ One of the high school-age workers explained how they use liquid nitrogen to freeze the mixture of dairy ingredients to make the ice cream. Please note that liquid nitrogen is stored in a cylinder located inside the shop under pressure (250–350 PSI). When released, the very cold liquid, at temperatures of –320 °F (–196 °C), is released into the environment. The liquid nitrogen cylinder was inside the shop, directly adjacent to the serving counter. I asked about safety, and she explained that ‘if the alarm goes off, they are supposed to go outside.’ Note how she explained that ‘they are supposed to go outside’; she did not say they immediately go outside. This is the issue: when liquid nitrogen is released into a confined space, for example, into the ice cream shop, the nitrogen quickly displaces the oxygen in the room and can result in people being killed due to oxygen deprivation. Due to nitrogen’s completely colourless and odourless properties, the victims are unaware of what is happening to them. In this book, you will see just how quickly this can happen and, unfortunately, how frequently it happens and how deadly it is.
This is exactly what happened at the Foundation Food Group, and six people were killed by hypoxia due to oxygen deprivation. Several others were hospitalized due to the effects of nitrogen exposure. This incident is covered in more detail in the What Has Happened / What Can Happen section of this book.
I asked the shop attendant if they had ever had a nitrogen release, and she explained, ‘Yes, just two weeks ago, a pipe broke on the tank, and the nitrogen was released.’ She said that the nitrogen (supercold) removed the lettering previously on the front lower part of the dairy counter, and sure enough, you could see that the lettering was smudged and essentially gone. She explained that this incident happened overnight when no one was in the shop.
After I returned home, I attempted to contact the business owner of the ice cream shop several times to no avail. Each time I call, I get a recording on the phone, something to the effect that this device is not set up to receive messages. I haven’t given up and would certainly like to discuss this with the business owner and hear a little more about how safety is managed at this location. I was in the Nashville area leading a safe operations training course recently and mentioned my experience at this ice cream shop. I was surprised to hear from several attendees that there are shops of this type in the Nashville area, and I have since learned that there are also shops of this type in New Orleans and other major cities across the United States. This ‘nitrogenated ice cream’ appears to be a national trend. I have since learned of other nitrogenated alcoholic drinks, taking advantage of the refrigeration qualities of liquid nitrogen and the aesthetic value of ‘smoking drinks.’
The stainless-steel tank is the compressed liquid nitrogen storage tank. The lettering on the tank says, ‘Selfie Station,’ where kids and others can have their pictures taken in front of it.
The caption says:
‘SELFIE STATION – SPARKY LOVES SELFIES….. TAKE YOURS HERE AND TAG US TO BE FEATURED ON OUR ACCOUNT. SPARKY WILL RANDOMLY PICK POSTS THAT HE LOVES AND SEND YOU A GIFT!!’
Ice cream shop interior: Key Largo, Florida.
Note that the lettering is missing from directly below the counter.
The lettering was removed by a release of supercold liquid nitrogen a couple of weeks before when a section of pipe associated with the nitrogen storage tank failed overnight. When I saw this and coupled it with my knowledge of the Georgia poultry processing facility where six workers were killed by nitrogen, this became the driver for trying to share these lessons learned and hopefully prevent another tragic incident from occurring.
This became the incentive to write this book and help get the message out about the safety aspects of working with or around nitrogen and other asphyxiants in any form. All nitrogen (and other asphyxiants) has the potential for the same hazards, including compressed nitrogen, liquefied nitrogen and pipeline-supplied nitrogen. They are all deadly because if released into a confined space, the nitrogen displaces oxygen, which is a hazard. One breath of nearly pure nitrogen and your brain shuts down, and even if you fall into clean air, you may not start breathing unless you are resuscitated. This is the severe hazard of nitrogen. Liquid nitrogen is also more likely to freeze your skin, resulting in frostbite or possibly severe cold burns due to the extremely cold temperature. Ingestion of even very small amounts of liquid nitrogen can destroy a victim’s internal organs. Other gases such as carbon dioxide (frequently used as a fire suppressant), argon (frequently used for welding) and helium, among others, have very similar characteristics and hazards.
In this book, I cover several cases of nitrogen asphyxiation and asphyxiation by other inert gases. If you work with or near equipment containing nitrogen or other inert gases, I encourage you to become familiar with these hazards. Nitrogen and other inert gases can be managed safely, but it only takes one slip or omission for people to be killed.
I later learned that a liquid nitrogen release occurred at a similar ice cream shop in Weston, Florida, where one worker collapsed unconscious, and two responders, a firefighter and a deputy sheriff, were also overcome. The news video of this incident shows the glass shop windows completely iced over. One person was admitted to the hospital for treatment, and the shop was closed for several days.
In addition to the personnel safety hazards created by using nitrogen as a refrigerant in enclosed spaces, ice cream made with liquid nitrogen has resulted in severe injuries due to ingesting small amounts of liquid nitrogen. I’ll talk more about this in the last chapter. Still, serious injuries to the digestive tract have occurred due to supercold nitrogen and the rapid expansion of the liquid nitrogen to vapour inside the digestive tract. As a result, at least one US agency has advised against consuming ice cream made with liquid nitrogen.
While I enjoy occasional ice cream, I can’t support this trend. I don’t support having a liquid nitrogen storage tank indoors where people, including children, are present. Knowing what has happened to others, I am also wary of the possibility of ingesting even a small amount of liquid nitrogen from eating something as delicious as ice cream.
In this book, we will spend most of our time reviewing the background of using nitrogen in industry and elsewhere, the hazards of working with and around nitrogen, and case studies associated with incidents involving nitrogen and nitrogen asphyxiation. Due to the hazards of other asphyxiants and the similarities with nitrogen, we will also discuss several other inert gases and cover several case studies where they were involved. Near the end of the book, there is also a summary of US Occupational Safety and Health Administration (OSHA) NITROGEN ASPHYXIATION INCIDENTS from the OSHA database that I think you will find interesting and useful. You may notice a little redundancy or a repeat of some information as you read this material. This is by design, and you will understand why when you realize the number of deaths that have occurred and how quickly it can happen.
You will also find an End of Chapter Quiz at the end of each chapter as a reminder of the important ‘learnings’ in the chapter and an End of Book Quiz near the end of the book. The answers to each quiz are available in the appendix. I encourage you to do a quick review using this guide to help you ensure that you have picked up on the important points made.
I hope you enjoy the book and have an opportunity to learn something about working with and around nitrogen and other inert gases and the safety aspects that go along with it. I strongly encourage you to share lessons learned with your peers. You may just save a life by doing so.
The photograph on the cover of this book was provided courtesy of the US Chemical Safety and Hazard Investigation Board (CSB).
Note to the Reader
The author has over 50 decades of experience in the petroleum industry, with operational experience in nearly all aspects of refining operations. Formally an operator and manager, including the role of Safety and Environmental Manager at a major US Gulf Coast refinery, he has led the process of safe operations training worldwide for petroleum refineries and petrochemical plants for the past nearly 20 years.
It is believed that the information provided in the book will help lead to improved safety performance in the petroleum and petrochemical industry and all other industries that use nitrogen or other inert gases. However, neither Safety Consulting International L.L.C., the author, M. Darryl Yoes, nor the company producing the documents contained herein warrants or represents, expressly or by implication, the correctness or accuracy of the content or the information presented here. This material is presented to improve operations safety worldwide and is not intended to be used as operating guidance or procedures. Any use of the material contained herein is done with the user accepting legal liability or responsibility for the consequence of its use or misuse.
Safety Consulting International, LLC, the author, or any other company or person, as outlined earlier, makes no claim, representation or warranty, expressed or implied, that acting in accordance with this book or its contents will produce any particular results with regard to the subject matter contained herein, or satisfy the requirements of any applicable federal, state or local laws and regulations. Nothing in this document constitutes technical advice. If such advice is required, it should be sought from an attorney, a qualified company or a qualified individual.
No material known to be copyrighted or proprietary has been intentionally used in this document without the owner’s express approval or permission. The author has made extraordinary efforts to contact all owners of images used in this book to secure consent to use the photographs. All information presented is readily available in the public sector or represents the author’s experience and over 50 years of collecting process safety information. The copyright owner approved most images; those without attribution were taken by the author. There are several where, after an extensive search, the original could not be found; these are noted as such.
About the Author
M. Darryl Yoes is a refinery supervisor and manager with practical experience, having spent over 50 years in the refining industry. He began his career as a Process Apprentice at one of the largest US Gulf Coast refineries. After quickly advancing through several supervisory and management assignments, including first and second-line supervisor positions in process, mechanical and technical, he advanced to the position of Risk Management Advisor. He then became the Safety, Health, and Environmental Manager of one of the largest petroleum refineries in the world.
He either led or participated in numerous process safety incident investigations, including those involving the tragic loss of life. He served as an emergency coordinator and incident manager in the role of refinery superintendent and has extensive experience managing other emergency operations, including oil spill response operations. He has also led or participated in numerous process hazard analysis studies, as well as in operations integrity and safety risk assessments at major US and European petrochemical sites. He has also served as the Safety Manager for major construction projects at US refineries.
Mr. Yoes continues process safety management consulting for refining and petrochemical plants and for construction safety management for major construction projects across the United States and is a course leader and facilitator for petrochemical plant’s Operations Safety Management training designed for refinery and petrochemical plant management, supervision, engineering and plant operators. He has led comprehensive process safety operations training courses in essentially all regions of the world, including North and South America, Asia, and Europe, to share lessons learned from industry process safety incidents involving loss of containment of flammable or toxic materials leading to fire, explosions and injuries or fatalities. The Safe Operations Training presents practical methods or work practices to help avoid a reoccurrence of these types of incidents.
He is the author of another Wiley textbook and online process safety resource titled ‘Process Operations Safety – The What, Why, and How Behind Safe Petrochemical Plant Operations,’ which is available at most bookstores, Amazon, and online. This book is a comprehensive overview of process safety in petroleum refineries and petrochemical plants and is a valuable resource to operators, plant supervisors, engineers, and others responsible for process operations safety. To a significant extent, the content of the Safe Operations Training course is reflected in this book.
Mr. Yoes is also the founder and President of Safety Consulting International, LLC, which developed this helpful guide to prevent process safety incidents. He is employed by EcoScience Resource Group, LLC, in Baton Rouge, a firm specializing in developing process operations training manuals, process operating and environmental procedures, and operator training guides for the petroleum refining and petrochemical industries.
Chapter 1The Properties, Uses, and Safety Hazards of Nitrogen
The six fatalities that occurred at the Foundation Food Group facility during January 2021, coupled with my visit to the ice cream shop in Florida in early 2024, with the liquid nitrogen tank located inside the shop, made me realize how little the population understands the hazards of nitrogen and other inert gases. Nitrogen is perfectly safe when stored and used so that release or loss of containment is prevented in an enclosed space or other areas where personnel are present and ventilation is limited. These gases are inert. However, exposure to concentrated mixtures with air can be and has been deadly. This book will provide more details on what has happened and what can happen when inert gases like nitrogen are released. We will discuss the hazards of these gases, how they can affect the human body and how this contact can be avoided. We will also review several case studies where this has occurred and, unfortunately, how people have died when this occurs.
The US Environmental Protection Agency (EPA) Cameo Database tells us that nitrogen is a colourless and odourless gas. It is non-combustible and non-toxic. Nitrogen makes up the major portion of the atmosphere (78%), but it does not support life by itself. We also know that nitrogen is frequently used in food processing, purging air conditioning and refrigeration systems. Nitrogen can result in asphyxiation by displacement of oxygen in the air. Also, pressurized nitrogen cylinders under prolonged exposure to fire or heat may rupture violently and become projectiles.
Nitrogen is readily available in the environment and makes up 78% (by volume) of the air we breathe. The remainder is 21% oxygen and a minimal amount of argon. Nitrogen is a non-poisonous gas; however, people and animals can die due to nitrogen concentration. They die not from nitrogen but due to oxygen deprivation. Nitrogen displaces oxygen from the air we breathe. In other words, when the nitrogen concentration increases, the oxygen concentration decreases.
Nitrogen is readily available by cryogenic fractionation of air to extract it for industry and other uses. It is slightly lighter than air and is slightly soluble in water. Liquid nitrogen boils at −320 °F (−196 °C) and contact with it can cause significant cold burns if it touches the skin or flesh.
One volume of liquid nitrogen expands to approximately 700 volumes of gas. An unplanned release of liquid nitrogen, for example, from a liquid nitrogen tank, will fill a standard-size room with concentrated nitrogen in seconds. People in the room can be quickly overcome by oxygen deprivation, and they can die, and this can happen in minutes. Cold nitrogen is heavier than air, and it will accumulate at ground level during a release. When liquid N2 is exposed to air, the cloudy vapour you see is only the condensed moisture from the air, not the N2 gas. Remember, nitrogen gas is invisible and odourless, and this is the danger!
Nitrogen condenses at its boiling point, −320.4 °F (−195.8 °C), to a colourless liquid lighter than water (liquid nitrogen). Liquid nitrogen is stored in specially designed pressure vessels designed to protect the super low temperature of the stored cryogenic liquid. When withdrawn, the temperature is −320 °F (−195 °C), making it very useful as a coolant or refrigerant. This characteristic makes liquid nitrogen useful as a refrigerant for food processing, pharmaceutical manufacturing and other commercial uses.
Nitrogen is non-flammable and does not support combustion. Therefore, it is often considered an inert gas (although it is not truly inert).
Safety hazards of nitrogen:
There are three primary hazards associated with nitrogen. In either form, as a liquid or gas, the deadly characteristic is that nitrogen quickly displaces oxygen from the environment. This has resulted in many incidents of accidental asphyxiation of workers. As stated earlier, it is not the nitrogen that kills; people die due to oxygen deprivation when nitrogen displaces oxygen. See the case studies in this book and the appendix for a discussion of nitrogen-related incidents.
Nitrogen (A frequent cause of fatalities and the primary subject of this book – this is a summary; refer to the Safety Data Sheet (SDS), or sometimes referred to as the Material Safety Data Sheet (MSDS) for additional information):
A general description of nitrogen from the US Environmental Protection Agency (EPA) Cameo Chemicals Database:
Nitrogen is a colourless and odourless gas. It is non-combustible and non-toxic and makes up the major portion of the atmosphere, but it does not support life by itself. Nitrogen may cause asphyxiation by displacement of air containing oxygen, which is needed to sustain life. Under prolonged exposure to fire or heat, containers may rupture violently and rocket.
Health hazards of nitrogen from the EPA Cameo Chemicals Database and the Safety Data Sheet:
Vapours from liquefied gas may cause dizziness or asphyxiation without warning. The victim may not be aware that they are being overcome. Vapours from liquefied gas are initially heavier than air and spread along the ground.
High concentrations of nitrogen may cause asphyxiation. Symptoms may include loss of mobility and loss of consciousness. The victim may not be aware of asphyxiation. To protect yourself, wear a self-contained breathing apparatus (SCBA) when responding to someone who has been overcome. Remove the victim to an uncontaminated area and keep the victim warm and rested. Call a doctor. If breathing ceases, apply artificial respiration. Additional hazards associated with exposure to oxygen deprivation are highlighted in Chapter 3 including a chart highlighting the effects of low oxygen concentrations on the body.
If you are working near a vessel that is being purged with nitrogen, appropriate warnings and barricades must be in place to prevent personnel from entering areas that may have an oxygen deficiency. Barricades must be designed to keep personnel from entering these areas, including all areas where nitrogen is vented into the atmosphere.
Personnel should be prevented from entering platforms near open access plates or on process vessels with nitrogen venting. Personnel working near nitrogen venting must be properly outfitted with either hose line-supplied breathing air or protected by a self-contained breathing apparatus. Additionally, personnel while wearing self-contained breathing air should continuously monitor other workers who are working in or near an area where nitrogen purge is in progress. No one should be allowed on the platform or near the vessel opening where nitrogen is venting without breathing air.
Warning: As a reminder, a cartridge or chemical respirator is not sufficient for breathing protection when exposed to an oxygen-deficient atmosphere. The respirator must have a supply of hose-line-supplied or self-contained breathing air.
Do I have to be inside a confined space to be overcome by nitrogen?
NO, you do not! There have been several cases where workers have been outside a vessel being purged with nitrogen and collapsed due to oxygen deprivation and fell into the vessel and died, or they were overcome, fell and died from the fall.
The second hazard is associated with liquid nitrogen. Liquid nitrogen is a cryogenic liquid and is stored in a pressure vessel specially designed to maintain liquids at extremely low temperatures. It is stored at a temperature of −320 °F (−196 °C) and is an extreme risk of causing cold burns. A cold burn is no different from a hot liquid or a thermal burn. It can result in damage to the skin and to the underlying tissue and can require skin grafts and treatment, not unlike a thermal burn.
When liquid nitrogen is released into the atmosphere, it quickly forms a white fog by freezing the moisture in the air. It may also freeze anything nearby and can create an oxygen-deficient atmosphere.
The third significant hazard with liquid nitrogen is the potential ingestion of even a small amount of the liquid, for example, in ice cream or a cold treat. I’ll discuss this in more detail in future chapters.
Humans must breathe oxygen to survive and suffer adverse health effects when the oxygen concentration drops below 19.5%. This can happen when the oxygen in the work environment is displaced by an inert gas such as nitrogen, argon, carbon dioxide or another inert gas. Some light hydrocarbons, although not inert, may have similar effects.
The US Occupational Safety and Health Administration (OSHA) has developed a nice chart that clearly details the effects of an oxygen-deficient atmosphere on personnel who may be unaware that this exists around them. This chart is included in Chapter 3 and details that workers who are undergoing any form of exertion rapidly become symptomatic when the oxygen level drops below about 19.5%. At 12–16%, they have increased breathing rates, accelerated heartbeat, and impaired attention, thinking, and coordination, even when at rest. As the oxygen concentration continues to drop, workers may experience poor judgement and exhaustion, even with minimal exertion, and they ultimately have heart failure (cardiac arrest) and die.
The following is extracted from the Chemical Safety and Hazard Investigation Board report on the nitrogen fatalities at the Valero Delaware City Refinery.
‘Workers may be unaware of another dangerous complication: inhaling nitrogen or other inert gas suppresses the brain’s breathing reflex response. The breathing reflex is controlled by the amount of carbon dioxide in the blood rather than the shortage of oxygen. Normally, the ability to voluntarily hold one’s breath is eventually overwhelmed by the brain’s respiratory control centre, which is triggered by the increased carbon dioxide concentration in the blood, combined with a drop in the blood’s pH. If high purity nitrogen or other inert gas is inhaled, the body may simply stop breathing, as carbon dioxide accumulation in the blood is insufficient to stimulate the breathing reflex (Lumb, 2005)’.
How long does it take for the oxygen level to drop to a dangerously low level when liquid nitrogen is released into a confined space?
The answer is that when nitrogen is released into the environment, the oxygen level only takes a few minutes to reach deadly concentrations. Also, it is just as important to understand that the victim or victims will not perceive or understand what is happening to them. There is no odour or other indication that they are in danger of being killed.
Case Study Documented by the National Library of Medicine and National Center for Biotechnology Information:
These US National institutions documented the following tragic case study: This case study confirms that the oxygen level will quickly drop to very low levels when nitrogen is released into the environment, especially in confined spaces or areas where there is little air circulation.
‘A 27-yr-old postgraduate student was found lying on the floor of an unsealed underground dry area, where a valve-opened empty cylinder of liquid nitrogen (150 L) (5.3 Cu Ft) was connected to a cap-removed empty Dewar-flask (10 L) (.3 Cu Ft) via a copper infusion tube.
It is obvious that the student was draining liquid nitrogen from the cylinder into the flask when he was overcome by the lack of oxygen, collapsed and subsequently died. The liquid nitrogen was to be used in a subsequent class study.
No injury was found externally or internally. There were petechiae in the bilateral conjunctive and periorbital skin (pinpoint, round spots forming around the skin around the eyes, sort of like a rash).
The dry area (where the student was collecting the liquid nitrogen), measured 300 × 130 × 260 cm (9.8 Ft. × 4.3 Ft. × 8.5 Ft.)., had a communication to the basement of the research building by a window measuring 90 × 60 cm (3 Ft. × 2 Ft.) in size at 130 cm (4.3 Ft. above the floor).
The scene reconstruction and atmosphere gas analysis revealed that the O2 concentration at 60 cm (2 Ft.) above the base dropped to 12.0% in 3 min and 10 sec, 10.0% in 8 min and 53 sec, 6.0% in 18 min and 40 sec, and 4.2% in 20 min and 28 sec. The primary cause of death was asphyxia by evaporated liquid nitrogen’.
These extremely low oxygen levels will not sustain life, and this case study confirms that they will occur within minutes of a release of liquid nitrogen into a confined space. Please refer to Figure 1.1 for a visual of the rapid drop in available oxygen resulting in this fatality.
Figure 1.1 National Library of Medicine, National Center for Biotechnology Information data confirm that the oxygen level in a confined space will quickly drop to very low levels in minutes, ensuring certain death for those exposed.
This chart, reconstructed using data from the National Library of Medicine, illustrates the rapid decline in available oxygen that resulted in a fatality. Thanks to the National Library of Medicine for making this data available.
The minimum safe oxygen concentration is 19.5%, as defined by the US Occupational Safety and Health Administration (OSHA). OSHA says health effects start when oxygen concentrations are below 19.5%.
In this incident, the oxygen level dropped below 19.5% in less than a minute and to 12% in 3 minutes. This is well below the level required to sustain life. Within 20 minutes, the oxygen level was at around 4%. This means certain death for everyone who was exposed.
The 27-year-old postgraduate student was found non-responsive in an underground dry area adjacent to a research building lying on plastic pallets. He was lying beside an empty Dewar flask connected to an empty liquid nitrogen cylinder. The valve on the cylinder was in the open position, indicating that the student was filling the flask when he was overcome by the lack of oxygen (due to a release of nitrogen vapours). The larger nitrogen cylinder had been filled the day before this incident. Please refer to Figure 1.2, which illustrates the empty liquid nitrogen cylinder connected to a smaller nitrogen Dewar flask. The student’s body was found lying adjacent to the empty cylinder.
Figure 1.2 Location of the nitrogen-induced fatality.
Source: National Library of Medicine (NLN), National Center of Biotechnology Information / Public domain. NLM is part of the National Institutes of Health (NIH), US Department of Health and Human Services, and is located in Bethesda, Maryland.
Please note the liquid nitrogen cylinder is set up to drain into the Dewar flask, potentially releasing nitrogen vapours into the surrounding environment.
After seeing this, please give more thought to my ‘nitrogenated ice cream’ story in the Foreword section of this book. Please note from the graph (Figure 1.1) that the available oxygen dropped below the OSHA ‘Deficient Oxygen’ criteria of 19.5% in about 1 minute. In other words, the nitrogen quickly displaced the available oxygen in the room. The available oxygen concentration dropped rapidly and, within the first couple of minutes, was well below that required to sustain human life.
Going back to the ice cream shop, what if the liquid nitrogen release, which occurred overnight the week before, had occurred during the day when the shop was full of teenage attendants and children? Possibly, the alarm would have sounded, and there would be a white fog, but there would have been no odour or other indication that their lives were at risk. The teenage attendant explained that ‘they are supposed to go outdoors if the alarm goes off’ – she didn’t say they will immediately go outdoors if the alarm goes off, and there was no sense of urgency or even an understanding of the potential hazard.
I am very concerned about having liquid nitrogen tanks and fittings inside an enclosure like an ice cream shop – or any enclosure. We also know a liquid nitrogen release occurred at a different ice cream shop in Weston, Florida, sending responders to the hospital for oxygen deprivation injuries. I can’t resist thinking if they realized how close they were to death.
The case study, as documented by the National Library of Medicine and National Center for Biotechnology Information, confirms that in the event of a release of liquid nitrogen, the oxygen level would quickly drop to levels well below that required to sustain life.
To expand on this point further, liquid nitrogen has an expansion ratio of 1:696. For example, 10 gallons equals 1.34 cubic feet. If we were to spill only 10 gallons of liquid nitrogen into a small room, for example, an ice cream shop, we would release 933 cubic feet of nitrogen into a confined space.
This would have an effect very similar to the case study shared by the National Library of Medicine, where one person was killed by asphyxiation due to nitrogen, and the Chemical Safety Board report on the Georgia poultry processing plant, which resulted in six deaths. In this example, the available oxygen level in the room would almost immediately drop to below what is required to support human life.
Transport and storage of liquid nitrogen and other cryogenic gases:
Liquid nitrogen is shipped and stored in specially constructed double-shell tanks. These tanks, sometimes called cylinders, are specially constructed to hold the cryogenic liquids, which are super cold and are designed with a vacuum between the inner and outer shell and several layers of insulation to prevent ambient heat from penetrating the shell to the cold liquid inside. These large cylinders allow the transport of a significant amount of nitrogen; remember, liquid nitrogen expands nearly 700 times when it vapourizes to gaseous nitrogen. Also, liquid nitrogen is a cryogenic liquid meaning that it is supercold and requires very little pressure when compared to nitrogen in a pressurized gaseous state.
Consumers of liquid nitrogen should be aware that ambient heat will penetrate through the cylinder shell and the insulation to the liquid and gradually increase its temperature. This will result in vaporization and a build-up of pressure in the cylinder, referred to as ‘head pressure’. This pressure will periodically vent off through the loosely fitting cap or the relief valve. I do not believe liquid nitrogen storage should be in a confined area due to the potential for a release, but if it is, the relief valves must vent outdoors. We must recognize that if the cylinders are located indoors and even with the relief valves venting outdoors, there is still the possibility of a pipe or fitting failure, such as what happened at the ice cream shop.
The uses of nitrogen:
Nitrogen is the most widely used industrial gas, especially by petroleum refineries and petrochemical plants. It is also widely used by pharmaceutical manufacturers, glass and ceramic manufacturers, steel and other metals refining and fabrication companies, and pulp and paper manufacturers. It is commonly known as nitrogen or N2 but also reported to sometimes be referred to as GAN or GN when in its gaseous form or LIN or LN when in its liquid form (although I have never seen these references). Nitrogen is especially useful to the petroleum refining or petrochemical industry because it is an inert gas that eliminates oxygen, thereby preventing a reaction with hydrocarbons or other chemicals that may result in a fire or explosion.
As a gas, nitrogen may also be used for any or all of the following (Nitrogen has many uses – the following is not intended to be a complete list):
Nitrogen is used in food processing, purging air conditioning and refrigeration systems, and pressuring aircraft tires. It is also regularly used in petroleum refining and petrochemical processes for tank blanketing, purging oxygen-containing equipment, laboratory use, and instruments and analysers.
Nitrogen may be supplied by pipeline as compressed gas or delivered in a liquefied state in compressed storage tanks or tank trucks.
In the petroleum refining and petrochemicals industry:
Preparing equipment by purging hydrocarbons before opening equipment to the atmosphere.
Remove oxygen from piping and process vessels during start up and before bringing in hydrocarbons.
Nitrogen is also frequently used as a testing agent when pressure testing the ‘tightness’ of piping circuits or pressure vessels in preparation for a unit start-up after turnaround or maintenance repairs. This is especially true for tightness testing high-pressure circuits.
Blanketing tanks to prevent the accumulation of flammable mixtures or products that are sensitive to air.
For inerting equipment prior to maintenance or mechanical work. For example, ensuring that process vessels such as reactors are essentially free of oxygen for catalyst replacement when the catalyst is pyrophoric. This prevents the catalyst from self-ignition by contacting air.
Purging equipment of oxygen and other reactive gases before placing it into long-term storage or ‘mothballing’. This is done to prevent oxidation or corrosion during storage.
Pressurized nitrogen may be used to clear plugs in pipelines or to pig lines for cleaning or prior to inspection or maintenance.
Nitrogen may also be used to pressurize tank cars or railcars to aid in offloading products to storage tanks or other dispositions. Nitrogen is inert and will not react with the hydrocarbons or other chemicals that may be in the railcar.
For some process and laboratory analyser operations. Process instrumentation or analysers are frequently purged with nitrogen gas.
For specific welding operations to eliminate air that can interfere with the welding process, contaminating the weld.
In the food processing industry:
Liquid nitrogen is used as a refrigerant to flash-freeze food products and prepare to ship to the customer.
Liquid nitrogen is also used as a refrigerant to flash-freeze dairy products to make ice cream or cold treats or fuming drinks such as dragons’ breath.
Other uses for nitrogen as a gas:
Nitrogen is sometimes used to inert aircraft fuel tanks to prevent an explosive mixture in the vapour space. Nitrogen is inert and displaces oxygen, preventing a flammable mixture from occurring in the storage tanks.
Nitrogen is important to support plant growth and can be added to the soil as an ingredient in fertilizers.
Nitrogen is frequently used as a filler in light bulbs to eliminate oxygen, thereby preventing combustion of the tungsten filament.
Nitrogen is widely used in pharmaceuticals and is in every major pharmacological drug class. For example, nitrogen is in most antibiotics.
Nitrous oxide is sometimes used as an aesthetic.
Nitrogen forms nitric oxide and nitrogen dioxide with oxygen, ammonia with hydrogen and nitrogen sulphide with sulphur. Some nitrogen compounds can also be formed naturally through biological activity.
As a liquid for storage or transport (liquid nitrogen from pressurized cylinders or tank trucks):
Liquid nitrogen is a cryogenic liquid, that is, it is stored in a pressure vessel specially designed to maintain liquids at extremely low temperatures. When liquid nitrogen is stored, it is at a temperature of −320 °F (−195 °C), making it very useful as a coolant or refrigerant. Therefore, it has many uses in laboratories, or in the food processing industry, to flash freeze various foods for processing or for shipment. Liquid nitrogen is also used to preserve biological specimens such as sperm, blood or eggs.
It is also sometimes used in the field to freeze lines when isolation valves are leaking through.
Liquid nitrogen, when released to near atmospheric pressure, expands 700 times in volume. Therefore, it is also used to store large quantities of nitrogen or transport nitrogen gas in large quantities.
At high temperatures and with the aid of catalysts, nitrogen can combine with some metals to form nitrides. For example, nitrogen and catalysts can combine with lithium, magnesium and titanium at high temperatures to form nitrides. This is a valuable contribution to compounds that can be used as hard coatings or insulators.
Nitrogen is necessary to support some biological processes. For example, it is frequently used as a fertilizer, typically as ammonia or ammonia-based compounds. Some compounds formed with halogens and certain organic compounds can also be explosive.
End of Chapter 1 Review Quiz
Why is nitrogen an important compound for use in the petroleum refining and petrochemical process industry?
Answer(s):
Nitrogen is used for petroleum and petrochemical storage tank blanketing to prevent the accumulation of __________ __________ or for products that are sensitive to __________.
Answer(s):
Please explain why liquid nitrogen is frequently used as a refrigerant in food processing and the pharmaceutical industries.
Answer(s):
What properties make nitrogen more suitable as a gas to pressurize tank cars or railcars to aid in offloading products to storage tanks or other dispositions?
Answer(s):
Why is nitrogen sometimes used to blanket aircraft fuel tanks?
Answer(s):
Nitrogen makes up about ______% (by volume) of the air that we breathe.
Answer(s): Please select the correct answer(s).
52%
85%
78%
26%
Can you name four of the characteristics of nitrogen?
Answer(s):
When liquid nitrogen is released into the atmosphere, it quickly forms a white fog by freezing the __________ in the air. It may also freeze anything nearby and can create an oxygen-deficient atmosphere.
Answer(s):
One volume of liquid nitrogen expands to approximately _______ volumes of gas.
Answer(s):
An unplanned release of liquid nitrogen, for example, from a liquid nitrogen tank, will fill a standard-size room with concentrated nitrogen in __________. People in the room can be quickly overcome by oxygen deprivation, and they can ________.
Answer(s):
What mechanism makes nitrogen so dangerous to work with and around?
Answer(s):
Cold nitrogen is ________ than air; therefore, it will tend to concentrate along the __________ or when in a building or room, along the _________.
Answer(s):
Another significant hazard when working with liquid nitrogen is the possibility of _______ or ___________ from contact with the cold liquid.
Answer(s):
Why is nitrogen purge used before unit start-up for process piping and vessels?
Answer(s): Please select the correct answer(s).
As a verification that there are no leaks in the piping or vessels before introducing hydrocarbons.
To eliminate oxygen from the piping or vessels before introducing hydrocarbons.
To ensure that the piping or vessels will not fail during the start-up process, releasing hydrocarbons into the atmosphere.
As a verification that there will be no product contamination during the start-up process.
How is nitrogen added to plants to help support plant growth?
Answer(s): Please select the correct answer(s).
Liquid nitrogen is injected into the soil directly below the plants.
Nitrogen is converted into ammonia or ammonia-based compounds and used as fertilizer to support plant growth.
Nitrogen is fed to plants by creating a nitrogen atmosphere during the plant’s early life.
Nitrogen is converted into ammonia, and the ammonia is provided to the plant in the nursery.
Liquid nitrogen is a ___________ liquid; that is, it is stored in a pressure vessel specially designed to maintain liquids at extremely low temperatures.
Answer(s): Please select the most correct answer(s).
condensed
cryogenic
mixed
pure
When liquid nitrogen is stored, it is at a temperature of __________°F making it very useful as a coolant or refrigerant.
Answer(s): Please select the most correct answer(s).
212 °F
–200 °F
32 °F
–320 °F
Nitrogen is used for tank blanketing to prevent the accumulation of __________ __________ or for products that are sensitive to __________.
Answer(s):
Additional References
Air Products. Safetygram-7, Liquid Nitrogen, 1998.
https://www.bnl.gov/esh/shsd/pdf/compressed_gas/safetygram_ln2.pdf
EPA Cameo Nitrogen Safety Datasheet (Nitrogen, Refrigerated Liquid) (Cryogenic Liquid).
https://cameochemicals.noaa.gov/chemical/4069
National Library of Medicine and National Center for Biotechnology Information, Evaporated Liquid Nitrogen-Induced Asphyxia: A Case Report.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2526498/
American National Standard Institute (ANSI) and American Society of Safety Engineers (ASSE), Safety Requirements for Confined Spaces. ANSI/ASSE Z117.1-2003.
American Petroleum Institute (API) API Standard 2217A, 3rd edition, January 2005.
Guidelines for Safe Work in Inert Confined Spaces in the Petroleum and Petrochemical Industries
BP Process Safety Series, Institution of Chemical Engineers (IChemE), Hazards of Nitrogen and Catalyst Handling
Compressed Gas Association, Inc. (CGA), Handbook of Compressed Gases, 4th edition, 1999.
Compressed Gas Association, Inc. (CGA), Accident Prevention in Oxygen-Rich and Oxygen-Deficient Atmospheres. GA P-14-1992.
Compressed Gas Association, Inc. (CGA), CGA, 2001. Safety Bulletin Oxygen-Deficient Atmospheres, SB-2, 4th edition, 2001.
Di Maio VJM, Dana SE, Finkel, and Martin H., 2000. Guidelines for Hot Work in Confined Spaces, Recommended Practices for Industrial Hygienists and Safety Professionals, ASSE, 2000.
Gill JR, Ely SF, and Hua Z. Environmental gas displacement Three accidental deaths in the workplace.
Am J Forensic Med Pathol
. 2002;23:26–30.
Harris, Michael K., Lindsay E. Booher, and Stephanie Carter, 1996 Field Guidelines for Temporary Ventilation of Confined Spaces American Industrial Hygiene Association, 2000.
Kernbach-Wighton G, Kijewski H, Schwanke P, Saur P, Sprung R. Clinical and morphological aspects of death due to liquid nitrogen.
Int J Legal Med
. 1998;111:191–195.
Manwaring, J.C. and C. Conroy, 1990. Occupational Confined Space-Related Fatalities: Surveillance and Prevention
Journal of Safety Research
, Vol. 21, pp. 157–164.
McManus, Neil, 1999. Safety and Health in Confined Spaces, Lewis Publishers/CRC Press.
National Institute of Occupational Safety and Health (NIOSH), 1987. A Guide to Safety in Confined Spaces Publication 87–113, July 1987.
NIOSH, 1986. Preventing Occupational Fatalities in Confined Spaces, DHHS (NIOSH) Publication No. 86–110, January 1986.
OSHA, 1994. Permit-Required Confined Spaces, 29 CFR 1910.146, May 1994.
Rekus, John F., 1994. Complete Confined Spaces Handbook Lewis Publishers/CRC Press.
