ASTM G145-08(2023)

Standard Guide for Studying Fire Incidents in Oxygen Systems

SIGNIFICANCE AND USE
5.1 This guide helps those studying oxygen system incidents to select a direct cause hypothesis and to avoid conclusions based on hypotheses, however plausible, that have proven faulty in the past.
SCOPE
1.1 This guide covers procedures and material for examining fires in oxygen systems for the purposes of identifying potential causes and preventing recurrence.  
1.2 This guide is not comprehensive. The analysis of oxygen fire incidents is not a science, and definitive causes have not been established for some events.  
1.3 The procedures and analyses in this guide have been found to be useful for interpreting fire events, for helping identify potential causes, and for excluding other potential causes. The inclusion or omission of any analytical strategy is not intended to suggest either applicability or inapplicability of that method in any actual incident study.  
Note 1: Although this guide has been found applicable for assisting qualified technical personnel to analyze incidents, each incident is unique and must be approached as a unique event. Therefore, the selection of specific tactics and the sequence of application of those tactics must be conscious decisions of those studying the event.
Note 2: The incident may require the formation of a team to provide the necessary expertise and experience to conduct the study. The personnel analyzing an incident, or at least one member of the team, should know the process under study and the equipment installation.  
1.4 Warning—During combustion, gases, vapors, aerosols, fumes, or combinations thereof, are evolved, which may be present and may be hazardous to people. Caution—Adequate precautions should be taken to protect those conducting a study.  
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Jun-2023
• ICS: 13.220.99 - Other standards related to protection against fire
• Technical Committee: G04 - Compatibility and Sensitivity of Materials in Oxygen Enriched Atmospheres
• Drafting Committee: G04.02 - Recommended Practices

Relations

• Refers: ASTM E1188-23 - Standard Practice for Collection and Preservation of Information and Physical Items by a Technical Investigator
• Effective Date: 01-Sep-2023
• Refers: ASTM G124-18 - Standard Test Method for Determining the Combustion Behavior of Metallic Materials in Oxygen-Enriched Atmospheres
• Effective Date: 01-Nov-2018
• Refers: ASTM E860-07(2013) - Standard Practice for Examining And Preparing Items That Are Or May Become Involved In Criminal or Civil Litigation
• Effective Date: 01-Jun-2013
• Refers: ASTM E1020-13 - Standard Practice for Reporting Incidents that May Involve Criminal or Civil Litigation
• Effective Date: 01-Jun-2013
• Refers: ASTM E860-07(2013)e1 - Standard Practice for Examining And Preparing Items That Are Or May Become Involved In Criminal or Civil Litigation
• Effective Date: 01-Jun-2013
• Refers: ASTM E1459-13 - Standard Guide for Physical Evidence Labeling and Related Documentation
• Effective Date: 15-Feb-2013
• Refers: ASTM E1188-11 - Standard Practice for Collection and Preservation of Information and Physical Items by a Technical Investigator
• Effective Date: 01-Sep-2011
• Refers: ASTM E1492-11 - Standard Practice for Receiving, Documenting, Storing, and Retrieving Evidence in a Forensic Science Laboratory
• Effective Date: 01-Jun-2011
• Refers: ASTM E620-11 - Standard Practice for Reporting Opinions of Scientific or Technical Experts
• Effective Date: 01-May-2011
• Refers: ASTM G93-03(2011) - Standard Practice for Cleaning Methods and Cleanliness Levels for Material and Equipment Used in Oxygen-Enriched Environments
• Effective Date: 01-Apr-2011
• Refers: ASTM G124-10 - Standard Test Method for Determining the Combustion Behavior of Metallic Materials in Oxygen-Enriched Atmospheres
• Effective Date: 01-Nov-2010
• Refers: ASTM G128-02(2008) - Standard Guide for Control of Hazards and Risks in Oxygen Enriched Systems
• Effective Date: 01-Sep-2008
• Refers: ASTM G126-00(2008) - Standard Terminology Relating to the Compatibility and Sensitivity of Materials in Oxygen Enriched Atmospheres
• Effective Date: 01-Apr-2008
• Refers: ASTM E678-07 - Standard Practice for Evaluation of Scientific or Technical Data
• Effective Date: 01-Apr-2007
• Refers: ASTM E860-07 - Standard Practice for Examining And Preparing Items That Are Or May Become Involved In Criminal or Civil Litigation
• Effective Date: 01-Apr-2007

Overview

ASTM G145-08(2023): Standard Guide for Studying Fire Incidents in Oxygen Systems offers procedures and guidance for examining and analyzing fire incidents within oxygen systems. Developed by ASTM International, this guide aims to help investigators identify potential causes of fires in oxygen-enriched environments, assist in the prevention of future incidents, and encourage conclusions grounded in reliable hypotheses rather than plausible but previously disproven assumptions. While the standard does not guarantee that definitive causes can always be established, it equips technical personnel with tools, considerations, and a structured analytical approach to studying oxygen system fires.

Key Topics

• Incident Study Approach

  • Emphasizes prompt, thorough documentation (photography, artifact preservation, interviewing witnesses)
  • Encourages systematic analysis of equipment, procedures, and environmental conditions

• Direct Cause Analysis

  • Focus on distinguishing direct mechanical, thermodynamic, or procedural causes from indirect contributing factors
  • Examples clarify the difference between direct physical causes and related systemic issues

• Hazard Identification

  • Considers contamination, improper materials, faulty procedures, and operational deviations
  • Investigates contamination sources such as hydrocarbons, oils, and metal particles

• Safety and Precaution

  • Stresses the importance of safety measures during investigation due to potential hazardous residues
  • Advises the formation of multidisciplinary teams familiar with the equipment and procedures under study

• Limitations and Scope

  • Acknowledges that incident analysis is not an exact science; some causes may remain undetermined
  • Each incident is unique and requires a tailored investigative approach

Applications

ASTM G145-08(2023) is utilized across industries where oxygen systems are prevalent-including healthcare, aerospace, chemical, and industrial gas sectors. Practical applications include:

• Post-Incident Analysis: Essential for engineers, safety managers, and technical investigators studying fire events in oxygen-enriched environments to identify the root cause and prevent recurrence.
• Quality Control & System Design: Supports designers and quality assurance teams in understanding risks associated with material selection, system operation, and potential contamination.
• Training & Awareness: Functions as a foundational guideline for technical training, aiding personnel in recognizing hazardous conditions and performing effective hazard assessments.
• Legal/Regulatory Compliance: Assists organizations in aligning their investigative methods with internationally recognized standards, supporting robust incident documentation and reporting.

Related Standards

The guide is best utilized in conjunction with related ASTM, CGA, and NFPA standards for a comprehensive approach to oxygen system fire safety and investigation:

• ASTM G63: Guide for Evaluating Nonmetallic Materials for Oxygen Service
• ASTM G88: Guide for Designing Systems for Oxygen Service
• ASTM G93: Guide for Cleanliness Levels and Cleaning Methods for Materials and Equipment Used in Oxygen-Enriched Environments
• ASTM G94: Guide for Evaluating Metals for Oxygen Service
• CGA G-4.4: Industrial Practices for Gaseous Oxygen Transmission and Distribution Piping Systems
• NFPA 53: Fire Hazards in Oxygen Enriched Atmospheres
• NFPA 921: Guide for Fire and Explosion Investigations
• OSHA Process Safety Management Compliance Manual
• ASTM E1459: Guide for Physical Evidence Labeling and Related Documentation
• ASTM E1492: Practice for Receiving, Documenting, Storing, and Retrieving Evidence in a Forensic Science Laboratory

Value for Stakeholders

By following ASTM G145-08(2023), organizations can:

• Improve root cause analysis in fire incidents involving oxygen systems
• Enhance safety protocols and operational procedures
• Reduce the likelihood of fire recurrence and related downtime or liabilities
• Support legal defensibility and regulatory compliance through standardized investigation practices

Keywords: oxygen system fire investigation, ASTM G145, root cause analysis, oxygen-enriched environments, fire safety, contamination in oxygen systems, incident analysis, oxygen fire incidents, hazard prevention, oxygen system safety standards.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: G145 − 08 (Reapproved 2023)
Standard Guide for
Studying Fire Incidents in Oxygen Systems
This standard is issued under the fixed designation G145; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.1 This guide covers procedures and material for examin-
ing fires in oxygen systems for the purposes of identifying
2. Referenced Documents
potential causes and preventing recurrence.
2.1 ASTM Standards:
1.2 This guide is not comprehensive. The analysis of oxy-
E620 Practice for Reporting Opinions of Scientific or Tech-
gen fire incidents is not a science, and definitive causes have
nical Experts
not been established for some events.
E678 Practice for Evaluation of Scientific or Technical Data
1.3 The procedures and analyses in this guide have been
(Withdrawn 2022)
found to be useful for interpreting fire events, for helping
E860 Practice for Examining and Preparing Items That Are
identify potential causes, and for excluding other potential
or May Become Involved in Criminal or Civil Litigation
causes. The inclusion or omission of any analytical strategy is
E1020 Practice for Reporting Incidents that May Involve
not intended to suggest either applicability or inapplicability of
Criminal or Civil Litigation (Withdrawn 2022)
that method in any actual incident study.
E1138 Terminology for Technical Aspects of Products Li-
ability Litigation (Withdrawn 1995)
NOTE 1—Although this guide has been found applicable for assisting
E1188 Practice for Collection and Preservation of Informa-
qualified technical personnel to analyze incidents, each incident is unique
tion and Physical Items by a Technical Investigator
and must be approached as a unique event. Therefore, the selection of
specific tactics and the sequence of application of those tactics must be
E1459 Guide for Physical Evidence Labeling and Related
conscious decisions of those studying the event.
Documentation
NOTE 2—The incident may require the formation of a team to provide
E1492 Practice for Receiving, Documenting, Storing, and
the necessary expertise and experience to conduct the study. The personnel
Retrieving Evidence in a Forensic Science Laboratory
analyzing an incident, or at least one member of the team, should know the
G63 Guide for Evaluating Nonmetallic Materials for Oxy-
process under study and the equipment installation.
gen Service
1.4 Warning—During combustion, gases, vapors, aerosols,
G88 Guide for Designing Systems for Oxygen Service
fumes, or combinations thereof, are evolved, which may be
G93 Guide for Cleanliness Levels and Cleaning Methods for
present and may be hazardous to people. Caution—Adequate
Materials and Equipment Used in Oxygen-Enriched En-
precautions should be taken to protect those conducting a
vironments
study.
G94 Guide for Evaluating Metals for Oxygen Service
1.5 This standard does not purport to address all of the
G114 Practices for Evaluating the Age Resistance of Poly-
safety concerns, if any, associated with its use. It is the
meric Materials Used in Oxygen Service
responsibility of the user of this standard to establish appro-
G124 Test Method for Determining the Combustion Behav-
priate safety, health, and environmental practices and deter-
ior of Metallic Materials in Oxygen-Enriched Atmo-
mine the applicability of regulatory limitations prior to use.
spheres
1.6 This international standard was developed in accor-
G126 Terminology Relating to the Compatibility and Sensi-
dance with internationally recognized principles on standard-
tivity of Materials in Oxygen Enriched Atmospheres
ization established in the Decision on Principles for the
G128 Guide for Control of Hazards and Risks in Oxygen
Development of International Standards, Guides and Recom-
Enriched Systems
1 2
This guide is under the jurisdiction of ASTM Committee G04 on Compatibility For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and Sensitivity of Materials in Oxygen Enriched Atmospheres and is the direct contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
responsibility of Subcommittee G04.02 on Recommended Practices. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved July 1, 2023. Published July 2023. Originally approved the ASTM website.
in 1996. Last previous edition approved in 2016 as G145 – 08 (2016). DOI: The last approved version of this historical standard is referenced on
10.1520/G0145-08R23. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G145 − 08 (2023)
2.2 Compressed Gas Association (CGA) Standards: Discussion—Contamination and cleanliness are opposing
G-4.4 Industrial Practices for Gaseous Oxygen Transmission properties: increasing cleanliness implies decreasing contami-
and Distribution Piping Systems nation.
G-4.8 Safe Use of Aluminum Structured Packing for Oxy-
4. Summary of Guide
gen Distillation
4.1 Following a fire incident in an oxygen-enriched
2.3 National Fire Protection Association (NFPA) Standard:
atmosphere, the equipment, operating procedures, and area are
NFPA 53 Fire Hazards in Oxygen Enriched Atmospheres
considered in light of other incidents, potential contributing
NFPA 921 Guide for Fire and Explosion Investigations
factors, suggested analytical strategies, and demonstrated labo-
2.4 Occupational Safety and Health Act:
ratory results. The goal is to determine direct cause(s) of the
OSHA Process Safety Management Compliance Manual
incident in order to prevent a recurrence.
2.5 ASTM Adjuncts:
Video: Oxygen Safety 5. Significance and Use
5.1 This guide helps those studying oxygen system inci-
3. Terminology
dents to select a direct cause hypothesis and to avoid conclu-
3.1 Definitions—See Guides G63, G94, and G128 for the sions based on hypotheses, however plausible, that have
terms listed in this section.
proven faulty in the past.
3.1.1 oxygen compatibility, (also oxidant compatibility),
6. Abstract
n—the ability of a substance to coexist with both oxygen and
a potential source(s) of ignition at an expected pressure and
6.1 A series of possible causes and common scenarios are
temperature with a magnitude of risk acceptable to the user.
described to assist those seeking to understand incidents in
oxygen-enriched atmospheres. Many easily misinterpreted fac-
3.1.2 qualified technical personnel, n—persons such as
tors are described to help avoid faulty conclusions. Several
engineers and chemists who, by virtue of education, training,
suspected but unproven incident scenarios are described. Select
or experience, know how to apply the physical and chemical
laboratory data are presented to support assertions about direct
principles involved in the reactions between oxygen and other
causes of incidents.
materials.
3.1.3 oxygen-enriched, adj—a fluid (gas or liquid) mixture
7. Direct-Cause Analysis
containing more than 25 mole % oxygen.
7.1 In this guide, the direct cause of an incident is the
3.2 Definitions of Terms Specific to This Standard:
mechanical or thermodynamic event (such as breakage of a
3.2.1 incident, n—an ignition or fire, or both, that is both
component or near-adiabatic compression), the physicochemi-
undesired and unanticipated, or an undesired and unanticipated
cal property (such as heat of combustion), the procedure (such
consequence of an ignition or fire that was anticipated.
as a valve opening rate), or any departure(s) from the intended
3.2.2 direct incident cause, n—the mechanical or thermody-
state of any of these items, that leads directly to ignition or fire,
namic event (such as breakage of a component or near-
or both. A fire might also be the result of a financial decision,
adiabatic compression), the physicochemical property (such as
worker skill, or manufacturing process—all of which can be
heat of combustion), the procedure (such as a valve opening
viewed as causes—but such factors are addressed more prop-
rate), or any departure(s) from the intended state of any of
erly in a system hazard review. It is noteworthy that some fires
these items, that leads directly to ignition or fire, or both.
are anticipated and the risks (whether human or economic) are
addressed by such things as shielding (for example, to control
3.2.3 fractional evaporation, n—the continuous evaporation
human risk) or acceptance (for example, to address economic
of a quantity of liquid that results in a progressive increase in
risk). In these cases, a fire is not an “incident” unless some
the concentration of a less-volatile constituent(s).
aspect of the event exceeded expectations the initial parameters
3.2.4 Contaminant, n—unwanted molecular or particulate
(for example, the shielding did not provide the expected
matter that could adversely affect or degrade the operation, life,
containment, or the cost exceeded projections). This guide
or reliability of the systems or components upon which it
seeks to identify the material choice, equipment design, assem-
resides.
bly procedure, or other factor that led directly to the fire—and
3.2.5 Contamination, n—(1) the amount of unwanted mo-
more specifically, to distinguish the physical object or action
lecular non-volatile residue (NVR) or particulate matter in a
that caused the fire to start, to continue, or to be injurious or
system; (2) the process or condition of being contaminated.
destructive. Remedial actions are found in other documents
such as Guides G63, G88, and G94, and Practice G93, as well
as NFPA 53, CGA G-4.4, and G-4.8, OSHA Process Safety
Available from Compressed Gas Association (CGA), 4221 Walney Rd., 5th
Management Compliance Manual, and others.
Floor, Chantilly, VA 20151-2923, http://www.cganet.com.
7.2 Example—The direct cause of an incident may be
Available from National Fire Protection Association (NFPA), 1 Batterymarch
Park, Quincy, MA 02169-7471, http://www.nfpa.org.
concluded to be the use of an incompatible material, for
Available from Occupational Safety and Health Administration (OSHA), 200
example, a polyacetyl component was installed when a mate-
Constitution Ave., NW, Washington, DC 20210, http://www.osha.gov.
rial such as PTFE (polytetrafluoroethylene) or CTFE (chloro-
Available from ASTM Customer Service, 100 Barr Harbor Drive, West
Conshohocken, PA 19428-2959. Request Adjunct ADJG0088. trifluoroethylene) was preferred. The direct cause was not that
G145 − 08 (2023)
the budget was inadequate to cover the cost of PTFE; nor that Prevention can focus on cleanliness. Initiating Event: ignition
specific frictional properties of polyacetyl were required for of an incompatible oil. Direct Cause: contamination of the
mechanical purposes; nor that an incorrect part was installed in system.
error. Note that in this example, PTFE and CTFE might be
8.4.1.2 Example 2—Records may show that a component
needed to prevent or cope with ignition and fire, but that they
broke and produced a rub in a piece of machinery just before
might introduce non-fire-related issues such as loss of me-
an incident. This factor alone can ignite a fire and could be
chanical strength or production of toxic decomposition prod-
identified as the direct cause. If the component broke because
ucts when exposed to heat of compression. it contained a flaw, the flaw might be determined to be the
direct cause. However, if the part was selected because it
8. Elements of a Study offered economy, then the direct cause is still the inadequate
part—not a misguided effort to economize. Prevention in this
8.1 Overview—The study of an oxygen incident typically
case can focus on component quality. Initiating Event: friction
begins (preferably promptly) after the event has concluded.
during the rub. Direct Cause: Mechanical failure.
The fire is extinguished and any safety requirements or
8.4.1.3 Example 3—Deviation from an important operating
immediate needs are addressed (treating injuries, returning
practice, such as first equalizing downstream pressure with a
systems to a safe state, and so forth). Then the investigator can
bypass valve before opening a quick-opening valve, may be
begin to document the event, to preserve the artifacts, and to
established as the direct cause of a fire. The reasons for
detect how they may have been altered or compromised by the
departing from mandated practice are important, but they are
event and follow-up activities. Although many of these steps
not the direct cause. Here, prevention can focus on following
are itemized here, the intent of this guide is not to specify how
standard operating procedures. Initiating Event: approximately
or in what order they should be conducted. Rather, information
adiabatic compression. Direct Cause: incorrect operation.
is offered about certain procedures that have been effective in
8.4.2 An incident might be understood adequately when a
the past, as well as some that have led to faulty conclusions.
conservative tactic has been identified that would have pre-
Typically, good scientific and laboratory skills are useful and
vented or safely managed the event.
adequate. Forensic skills and procedures can be helpful in
8.4.2.1 Example 1—If an item of machinery cannot employ
many cases, but may not be practical in all. For example, the
oxygen-compatible materials because they compromise its
forensic Guide E1459 can assist with managing post-incident
operating economy, and it becomes the site of a fire and injures
artifacts, and related Practices E1492, E620, E678, E860,
someone, then the event may be understood adequately (re-
E1020, and E1188, as well as Terminology E1138, may have
garding preventing recurrence of injury rather than fire) when
other uses. However, when a forensic approach is needed
inadequate shielding or inadequate mechanical design or some
because a legal action is involved, the insights in this guide
other comparable factor is identified singly or in combination
may effectively supplement it.
as the direct cause.
8.2 Documentation—Urgent post-incident efforts include:
8.4.3 The study is complete when the direct cause has been
photographing or videotaping the site and any damaged equip-
determined. Preventing the repetition of an event is the
ment; obtaining system drawings, supporting design analysis,
function of a hazard review using well-established techniques,
process hazards analysis, and any other hazard-evaluation
including the use of related standards from ASTM Committee
materials; interviewing persons knowledgeable about the
G04. The hazard review may be integral to the incident study
system, operating procedures and the events before, during,
and may involve some or all of the same people, but it is a
and after the fire; collecting specimens, operating logs, and
separate activity for the purpose of this guide.
related information; and preliminary formulation and testing of
hypotheses.
9. Factors Affecting an Incident Study
8.3 Analysis—The principal effort in a study will be analysis
9.1 Missing Components—Following some oxygen
of the data and artifacts. This may require further examination
incidents, components have appeared to be absent, leading to
of the equipment and records, laboratory study of selected
speculation that the component was not installed or that its
items, and perhaps even laboratory simulation of the incident.
mechanical failure and passage through the system were at
8.4 Completion of Study—An incident study is complete
fault. Sometimes, the damage is so negligible that the possi-
when the qualified technical personnel involved in the study
bility that there was no fire is considered. These conclusions
conclude that the event is understood.
can be in error. In an oxygen-enriched atmosphere, combustion
8.4.1 An incident might be understood adequately when a
can be remarkably clean. A simple polymer may be converted
conclusion has been drawn about the direct cause of the event. totally into carbon dioxide and water, leaving no trace of its
The following examples show the distinction between direct
prior presence. If the component is small or if it has a low heat
causes and causes that are not physicochemical or thermody-
of combustion, there may be no evidence of heat damage. For
namic events.
example, PTFE seats in ball valves (which are large and have
8.4.1.1 Example 1—A substantial amount of hydrocarbon low heat of combustion) and nylon seats in cylinder valves
oil was introduced into a system just before an incident. This (which are small and have high heat of combustion) have
single factor may be identified as the direct cause of the fire. burned completely in some incidents with no melting of metal
Any reasons for introducing the lubricant may be important to components, no appearance of residual carbon, and no remains
a new hazard review, but are not the direct cause of the fire. of the polymer itself.
G145 − 08 (2023)
9.2 Contamination: fluorescent constituent in blood that might be mistaken for oil
9.2.1 When contamination is present in an oxygen system, contamination if injuries occurred and components became
the contaminant may serve to start the incident. The ensuing wetted with blood.
fire involving the polymers, metals, and contaminant may
9.2.5.3 The absence of an oil residue cannot rule out oil
consume the contaminant fully, leaving no indication of its
contamination as a potential cause of an incident. The need to
original presence.
avoid oil contamination is often ignored by system users/
9.2.2 When contaminant levels are high, they may produce
operators who are not well trained or knowledgeable about
so large an explosive event that the system integrity can be oxygen compatibility issues. There is a general view that
breached, and the fire can be extinguished without complete
lubrication is beneficial, and there are few convenient sources
combustion of the contaminant. Therefore, some of the con- of oxygen-compatible lubricants.
taminant may be found after an incident in the same regions of
9.3 Particle Impact:
the system where the fire occurred. In these instances, the
9.3.1 Impact and subsequent ignition of particles in oxygen
flammability of the contaminant can be so much greater than
systems has been demonstrated to have been the cause of
that of the metals and polymers that there may be only scant
several fires. This ignition mechanism is especially likely at
damage to the system materials.
and just downstream of locations where the velocity of the
9.2.3 Example—In laboratory tests of an oxygen system
oxygen is sonic (any location across which there is about a 2:1
component, hydrocarbon lubricating oil was introduced and
absolute pressure drop), and has been demonstrated at veloci-
ignited. When the amount of lubricant was small, a fire may or
ties as low as 150 ft/s (50 m/s) (2).
may not have resulted, but there was usually no trace of the oil
9.3.2 References 3-5 describe incidents thought to have
after the test. When the amount of lubricant was large, the
been affected by particle impact.
component was blown apart. Threads on the component parts
were stripped. A pressure gage was in fragments. After the 9.4 Debris Sumps—Many systems contain regions where
debris tends to collect. Particle debris can accumulate at low
event, neither melting nor consumption of the components was
observed, and the parts had an obvious coating of the oil. points or stagnant side branches. If the piping for a bypass
valve is connected to the bottom region of a horizontal run of
9.2.4 Carbon or Black Dust—In many incidents, a black
powder will be present on many surfaces. The powder could be pipe, debris that passes through the system may drop into the
stagnant upstream legs of the bypass run. If this valve is then
unreacted carbon from incomplete combustion of organic
materials either inside or outside the component. However, opened, accumulated debris is injected into the high-velocity
valve and may cause a fire either in the bypass run or further
some powders that look like carbon are not. For example, fires
involving aluminum in gaseous or liquid oxygen may produce downstream.
a black (and in some cases gray) powder that is largely
9.5 Heat of Compression:
unreacted aluminum. Indeed, such dust may be present as a
9.5.1 When a gas is compressed rapidly, its temperature
result of a fire involving aluminum, or it may be present
rises. The pressurization of a system tends to produce the
because of fabrication processes. In metal inert gas (MIG)
greatest temperatures within the gas initially in the system. The
welding, aluminum is vaporized and condenses as a black dust
increase in temperature can cause autoignition of some system
in the region of the bead. If this powder is present in an oxygen
components. This compression is nearly adiabatic and typically
system, it may be a cause of ignition, because it is very
occurs at system end points or trapped volumes. In extreme
flammable and has been observed burning even in air.
cases, heat of compression has produced some of the most
9.2.5 Oil—Oil in oxygen systems can be a severe hazard
explosive (rupturing and fragmenting components) and most
(1). Many oils, hydrocarbons in particular, are relatively
probable mechanisms of oxygen fires. In severe cases, a heat of
volatile in comparison to metals and polymers. Their autog-
compression fire may occur on the very first pressurization of
enous ignition temperatures are much lower than those of most
a system. Every incident should be examined for a mechanism
other materials (metals and nonmetals) used to fabricate
that may have enabled rapid gas compression and for where the
oxygen systems, including many materials not generally re-
compressed gas may have been located relative to the fire
garded as oxygen compatible. Therefore, heat of compression
damage.
can ignite oils much more easily. Furthermore, many oils burn
very rapidly, even explosively, and they are always a strong NOTE 3—Oxygen system fires require an energy source to trigger
ignition, as do most fires. Particle impact and compression heating were
candidate as the cause of an oxygen incident.
briefly described above since they are very often implicated in oxygen
9.2.5.1 Simple ultraviolet black light inspection of a site and
system fires; however, several other ignition mechanisms are known to
incident artifacts is a convenient way to identify the presence
occur. The most common ignition mechanisms are discussed in greater
of some oils. Many oils do not fluoresce. Therefore, the
depth in Guides G88 and G128.
discovery of oil-like fluorescence suggests oil as a potential
9.5.2 References 6-10 describe theory and experimental
cause, but the absence of fluorescence does not necessarily rule
work on heat of compression.
out contamination with oil as a cause.
9.6 Overpressure:
9.2.5.2 The use of ultraviolet light has other limitations.
9.6.1 A fire in an oxygen system can produce overpressure
Many materials besides oil fluoresce. For example, there is a
damage from pressures increasing beyond the system’s physi-
cal containment capabilities. It also can result from damage or
The boldface numbers in parentheses refer to the references listed at the end of
this guide. erosion that reduces system pressure containment capabilities
G145 − 08 (2023)
to below normal pressure exposure levels. Among the charac- above the burst pressure of the vessel, before the vessel
teristics that may be seen are bulging, bursting, venting, actually fails. This type of failure is also commonly known as
explosion, and fragmentation.
a “brittle” failure.
9.6.2 Bulging—Bulging or swelling of components can
9.6.4.1 Vessels that burst into many small pieces are often
occur at the site of an explosion or at weak regions of the
are associated with a detonation. Whereas deflagration is
system, or both. In brazed copper systems, it is common to see
relatively slow (see 9.6.3), in some very flammable conditions,
overpressure effects at annealed regions, such as just outside
called high-explosive, the velocity may achieve 3000 to 9000
brazed joints, where hardened tubing will be annealed and
ft/s (much faster than the speed of sound). In the latter instance,
therefore of lower strength. The presence of such bulging in
relief valves and vents are ineffective in limiting system
brazed copper joints in a local region only suggests a localized
pressures, and fragmentation often results with the production
explosive event. Bulging at many such joints may also indicate
of small fragments. However, it is not always possible to infer
a systematic pressure increase.
that fragments resulted from a detonation. In recent times, the
9.6.3 Bursting—Vessels that burst into several large pieces
testing of flammable metals in liquid oxygen has produced
typically have failed along weak regions or flaws and have
two-phase combustion and vessel fragmentation, and it is not
been exposed to either a small or slow explosive event (such as
certain at present that the combustion rates were in excess of
deflagration) or to a general systematic pressure rise that has
the speed of sound. This has led to the description of these
been relatively slow. Common gas phase combustion, or
events as “violent explosive reactions (VERs)” rather than
deflagration, often proceeds with a propagation velocity of the
detonations.
reacting zone of up to about 30 ft/s (10 m/s), well below the
speed of sound.
9.7 Time Delays—Most oxygen fire incidents are associated
9.6.3.1 Cylindrical vessels designed properly and pressur-
with a prior transient event, usually operation of a valve, that
ized slowly to failure often fail in a characteristic way; a tear
often is causal to the event. Most of the time the fire occurs
starts at a weak point in the wall of the cylinder and propagates
almost simultaneously with the transient event, but there can be
longitudinally in both directions until it reaches the head,
appreciable delays.
where it propagates along the edge of the head. Sometimes the
9.7.1 Example 1—An oxygen system is pressurized when a
head may be torn totally free, while the vessel often remains as
valve is opened. About 30 min later, a large leak develops in a
one piece. Fig. 1 shows how a ruptured cylindrical vessel might
closed PTFE-seated ball valve downstream, or the ball valve
look if flattened fully.
downstream is found to be hot. It is possible that the pressur-
9.6.3.2 In some metal alloys such as aluminum alloys,
ization produced heat-of-compression temperatures above the
piping is extruded with dies and mandrels in a way that can
ignition point of the PTFE valve seat. Because the valve was
produce weak longitudinal seams. Overpressure, either slow or
closed, the inert combustion products could accumulate and
fast, can cause tears along these seams, yielding several similar
slow combustion to the point where it may have taken 30 min
pieces. This can occur at pressures much lower than those
or more to breach the seat or to make the valve hot enough to
normally expected to cause fragmentation.
9.6.4 Fragmentation—When a vessel is fragmented into detect. In pressurized oxygen index tests of PTFE rod burning
many small pieces of dissimilar shapes and sizes, it usually in flowing oxygen/nitrogen mixtures near the end point, 30 min
suggests a very fast combustion that produced pressures well or more were required to burn a 75-mm (3-in.) long rod.
FIG. 1 Illustration of How A Ruptured Cylindrical Vessel Might Look if Fully Flattened
G145 − 08 (2023)
9.7.2 Example 2—Liquid oxygen flow to a waste vaporizer possibility of having played a crucial causal role either in
is interrupted, and the waste line clears itself. Several hours ignition or in the related kindling chain.
later, an explosion breaches a vertical run of piping where
9.11 Explosive Decompression:
liquid could collect. In this case, liquid with a low level of
9.11.1 When a gas permeates or dissolves into a material at
contaminants can fill a sump and slowly evaporate while
high pressure and the surrounding pressure is released at a rate
concentrating flammable constituents (see 10.2 on fractional
faster than the gas can diffuse out of the material, then the
evaporation). When a flammable mixture is developed, an
material becomes a sort of pressure vessel. If the material is an
ignition source can produce the delayed event.
elastomer, it can swell like a balloon, sometimes more than
9.8 Crevices—A crevice can be a potential ignition cause in doubling its apparent size (14,15). The internal pressure can
cause the elastomer to exceed its tensile strength, and it can
liquid oxygen (LOX) systems if it fills with liquid, especially
through a narrow passage or pore. When the vessel is drained burst. This is explosive decompression.
and warmed, high pressure and high velocity will develop in 9.11.1.1 Some O-ring design handbooks have described
the liquid, if the passage is small, as it tries to escape. If the explosive decompression as a potential source of ignition in
crevice is in a weld of a metal that produced MIG weld dust,
oxygen systems. The events believed to occur during explosive
it may contain fine, easily ignited particles that may become decompression (tearing, friction, high gas velocities, and so
entrained in the flow and impact a piping intersection or valve
forth) are all plausible elements of ignition. However, Com-
seat, causing ignition. If the liquid contains a low level of mittee G04 has not located any original data supporting this
contaminants, the liquid in the crevice may concentrate con-
potential mechanism, nor is Committee G04 aware of any
taminants as it evaporates (see 10.2 on fractional evaporation), laboratory tests that have produced ignition in this way, or any
and may inject sensitive hydrocarbon contaminants through the
incidents believed to have been caused by this mechanism.
passage. These events have been crudely demonstrated in
9.12 Intimate Mixture—Intimate mixing can lead to in-
laboratory tests and are believed to have resulted in some metal
creased flammability. Materials that dissolve in liquid oxygen
ignitions.
tend to be high explosives. Among the factors that lead to
9.9 Surface Discoloration: increased flammability in intimately mixed (homogeneous)
fuel and oxidant systems are adiabaticity, accessibility to
9.9.1 Pink Brass—During a fire, brass alloys may be ex-
oxidants, and so forth.
posed to brief, intense temperature or to corrosive chemicals,
resul
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