Definitions of Oxygen Enrichment/Deficiency Safety Criteria - eiga

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POSITION PAPER
Position Paper PP-14 –August 2006
Definitions of Oxygen Enrichment/Deficiency Safety
Criteria
Used in IHC Member Associations
1. Introduction
At various times in the past, in the preparation of industry standard documents and technical calculations, the IHC
(International Harmonisation Committee) members have defined different concentrations of oxygen in atmospheric
mixtures as “safe” or “unsafe” with respect to asphyxiation or enhanced combustion hazards. These significant
variations are now preventing any uniformity of presentation of acceptable oxygen limits in various EIGA documents
under revision or preparation, and potentially will affect the harmonisation process with IHC members because
different safety criteria have been previously adopted in some countries.
2. Purpose
This document is intended to consolidate the various definitions of oxygen enrichment/deficiency safety criteria
given in IHC member associations and equivalent national regulations.
3. Scope
The literature search is limited to publications in the following catalogues:
EIGA
CGA
BCGA
British Cryogenics Council
EH40 Occupational Exposure Limits
Sources of justification of concentrations defined such as “safe”, “harm effects”, “dangerous” are taken from the
publications cited in Appendix A, and not otherwise researched.
4. Conclusions and Recommendations
4.1 Oxygen Enrichment
Except within fairly narrow bands of disparity between documents or because of the relative publication dates of the
defining documents, there is no discrepancy between the various limiting oxygen concentrations defined as safe,
onset of danger etc. This is because the definitions are being given for different reasons in the documents cited.
There can be error when a new specialised document erroneously picks up an incorrect value because the wrong
definition has been taken as the basis, or the reason in the new document for the value is simply unclear.
The criteria to be used in the future for limits of oxygen enrichment are as follows:
• The maximum safe oxygen concentration for entry into a confined space that is being controlled or
measured because of the risk is 23.5 % total O2. The space should be ventilated sufficiently to obtain a
value approaching 21% O2 (i.e. indistinguishable from atmospheric air).
© EIGA 2006 - EIGA grants permission to reproduce this publication provided the Association is acknowledged as the source
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Position Paper PP-14 – August 2006 Page 2/5
• For cases of leakage, venting or uncontrolled release of oxygen into the outdoor atmosphere, there is no
risk of harm in clouds containing up to 25% O2. At anticipated level above 25% O2 it may be possible by
means of risk assessments to determine that such atmospheres can be safely entered with appropriate
control: e.g. there is no permitted smoking in an area where venting is possible, or hot work is controlled by
permit because of the risks of venting.
• For purposes of quantification, or for cases of reporting boundary conditions from predicted release cases
calculated by dispersion, there is an anticipated lethal risk from atmospheres with concentrations of 35% O2
and higher.
• Care has to be taken with regard to special circumstances such as definition of safety from releases
involving cold oxygen clouds that may accumulate in depressions or pits, or from atmospheric
concentrations that might enter air intakes to compressors, blowers or Heating Ventilation Air Conditioning
(HVAC) units, where the machinery design anticipates that only atmospheric air (i.e. 21% O2) could be
present.
• These criteria are only designed to cover cases of excess O2 concentration in anticipated atmospheric air,
they cannot be justified in any other cases e.g. oxygen – flammable gas mixtures or gases used for medical
purposes.
4.2 Oxygen Deficiency
Compared with the near uniformity of the oxygen limits, there is little agreement between the document sources on
the tolerability levels for oxygen deficiency. This appears to be because the base physiological data that are being
cited have significantly varying levels for the onset of different symptoms especially at levels where the situation is
reversible. Also loss of concentration, coordination or judgement are cited at relatively high O2 concentrations,
where there is no apparent danger in itself but for an individual engaged in a complex task there might be potentially
lethal knock on effects (e.g. falling, failing to carry out instructions, or accidents with machines or vehicles). The
result is a general principle to err on side of caution whatever the data. Nevertheless it is possible to recommend
criteria for different conditions under review on an equivalent basis to the results in 5.1 above.
The criteria to be used in the future for limits of oxygen deficiency are as follows:
The minimum safe oxygen concentration for entry into a space that is being controlled or measured because of the
risk is 19.5% total O2. The space should be ventilated sufficiently to obtain a value closer to 21% O2 (i.e.
indistinguishable from atmospheric air). There are applications with oxygen concentrations below 19.5% where
entry is permitted provided further precautions are taken in accordance with proper risk assessment and national
regulations (e.g. fire suppression).
• For cases of leakage, venting or uncontrolled release of inert gases into the outdoor atmosphere, there is
no anticipated risk of harm in clouds containing at least 17% O2.
• For purposes of quantification, or for cases of reporting boundary conditions from predicted release cases
calculated by dispersion, there is an anticipated lethal risk from atmospheres with concentrations of 12.5%
O2 and below.
• Care should be taken in determining what circumstances are anticipated for the people at the boundary
conditions in deciding to use the above values, which are for a person standing in the open air not under
stress or physical exertion. For example, if people within the anticipated release area are driving or using
tools or machinery, the risk or injury of death may result in atmospheres containing higher than 12.5% O2
because of the knock on effects from unnoticed loss of co-ordination or judgement.
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APPENDIX A Data Sources
1 Oxygen Enrichment
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Position Paper PP-14 – August 2006 Page 3/5
A. IGC Document 04/00/E “Fire hazard of oxygen and oxygen enriched atmospheres”
� For safe entry into a space that can subject to oxygen enrichment, the concentration should not exceed
22.5% O2. Concentrations of 23% or more are potentially dangerous.
B. BCGA Technical Report TR2 (1999) “
The probability of fatality in O2 enriched atmospheres due to spillage of liquid O2 (LOX)”
� The dangerous dose for LOX spills has been defined with the HSE as 35% total O2 concentration. (This is
demonstrated in the data presented as approximately 0.5% probability of fatality or serious injury for
members of the general public resulting from uncontrollable ignition sources).
� The report is justifying raising the dangerous dose level determined in the earlier BCGA TR1 report from
30% O2 by reference to recalculated data for the same probability of fatality cut-off criteria.
� Although not mentioned in the conclusions, there was no change to be made to the safe max.limit of oxygen
concentration of 25% derived in the earlier document because the variation in fatality rate between the two
documents was not significant.
C. OSHA 29 CFR1920.146 Hazardous atmosphere
� Hazardous atmosphere means an atmosphere that may expose employees to the risk of death,
incapacitation, impairment of ability to self-rescue (that is, escape unaided from a permit space), injury, or
acute illness from one or more of the following causes:
Atmospheric oxygen concentration below 19.5% or above 23.5%
D. BCGA Technical Report TR1 (1984) “
A method for estimating the offsite risks from bulk storage of liquefied oxygen (LOX).”
� The oxygen concentration below which no irreversible harm is anticipated to members of the general public
from a LOX spill was found to be 25% total O2 concentration. [Basis is calculated risk of fatality or serious
injury at 0.02% from uncontrollable ignition sources – mainly burning clothes with ash from smoking.]
BCGA Technical Report TR2 Table 1
Probability of Fatality in Oxygen Enriched Atmosphere
Oxygen concentration %
Probability of Ignition Source Being Present %
25 30 35 40
Based on 30% of population as smokers and 10% of time
away from work spent smoking (7.5 minutes per cigarette
3.5 3.5 3.5 3.5
Probability of Igniting Clothing
Based on time to ignite clothing; Type of ignition source
(match, lighter, cigarette). Type of material.
Probability of Fatal or Serious Injury
Based on burning rate of material and reaction time of victim
5 30 50 90
10 16 29 90
Probability of Fatal or Serious Injury % 0.018 0.17 0.53 2.8
E. IGC Document 75/01/E/Rev “Determination of safety distances”
� Defines harm criteria as being at levels of severe distress, high probability of a need for medical attention,
likelihood of serious injury, or a probability of fatal injury. There are corresponding no-harm criteria of
situations to which nearly all individuals could be exposed without experiencing or developing irreversible or
other serious health effects, or symptoms that could impair ability to take appropriate immediate corrective
actions. [These criteria were to be used for risk-based calculations and therefore represented target
outcome frequencies.]
� The harm value for O2 enrichment is taken to be 30% O2 and above, and the no-harm value of up to 25%
O2. [Basis for this was the BCGA TR1 report: the preparation of this document crossed with the BCGA
update as TR2 and therefore does not reflect the revised dangerous dose adopted by BCGA.]
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F. IGC Document 13/02/E “Oxygen pipeline systems” [This document is dealing with transportation of
compressed O2 or O2 rich gases rather than concentrations in the atmosphere, and is consequently mainly
concerned with material burning properties in O2/N2 mixtures, that are affected by conditions of pressure,
temperature and velocity of flow.]
� Defines treating the flow gas as oxygen for any mixture above 23.5% O2
� However has criteria defining the gaseous oxygen as low purity from 23.5% up to 35% O2, up to which level
relatively minimal precautions (in terms of velocity, cleanliness, selection of materials) are necessary to
avoid kindling a fire and enhancing the combustion process because of the oxygen.
G. CGA P-39 (2003) “Oxygen-rich atmospheres” [Superseded P-14 quoted in various documents “Accident
prevention in O2 rich and O2-deficient atmospheres”]
Defines oxygen-rich atmosphere as air or gas mixtures exceeding 23.5% O2 by volume. [Standard implies
a hazard from this level by describing all oxygen-rich atmospheres as if pure O2]
2 Oxygen Deficiency
A. IGC Document 44/00/E “Hazards of inert gases”
• Situation is hazardous as soon as the oxygen concentration is below 18%
• Death is almost certain below 10% O2
• No justification is given in the document for theses conclusions
B. BCGA CP21 ( 2004) “Bulk liquid argon or nitrogen at user premises” [All relevant BCGA documents on
N2/Ar subsequent to this reproduce the same information word-for-word.]
• Atmospheres with oxygen concentrations below 18% are potentially dangerous and entry into atmospheres
below 19.5% O2 not recommended
• Data of effects at lower concentrations given as follows (text abbreviated). [No source cited]
11- 14% O2
8-11% O2
6-8% O2
0- 6% O2
Diminution of physical / intellectual performance without knowledge
Possibility of fainting without warning
Fainting but resuscitation possible if immediately applied
Death practically inevitable
C. IGC Document 75/01/E “Determination of safety distances”
• Harm / no-harm definitions as for oxygen enhancement. Gave no-harm O2 level as down to 18% oxygen
with harm from 11% O2 or less. [Basis for this was 1990 version of 44/00/E above, which had 16% for
hazardous upper limit rather than 18% as above.]
D. British Cryogenics Council: Cryogenics Safety Manual (3 rd edition)
• Quotes 1939 source (Alexander and Hinwick) as below (text abbreviated) without giving a conclusion on
what is a safe O2 deficiency
Down to 14% 1
O2
st stage. Symptoms: higher breathing and pulse. Attention /
coordination / thought affected. Not noticed by individual
14-10% O2 2 nd stage. Conscious but physical problems increase
10-6% O2 3 rd stage. Physical collapse and permanent damage without warning
Below 6% 4 th stage. Unconsciousness resulting in death
• HSE advice in United Kingdom Occupational Exposure Limits standards indicate 19% O2 as a statutorily
general limit for safe minimum O2 limits (e.g. atmospheres in Mines)
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E. CGA Safety Bulletin SB-2 (2003)
• Defines unsafe as oxygen concentrations below 19.5% O2 (from OSHA regulation)
• Quotes data as follows (text abbreviated). Adapted from ANSI Z88.2, Respiratory Protection. These
indications are for a healthy average person at rest. Factors such as individual health (such as being a
smoker), degree of physical exertion, and high altitudes can affect these symptoms and the oxygen levels
at which they occur. No source cited.
19.0% O2
16.0% O2
14.0% O2
12.5% O2