Chapter V. Additional
Information on Hazards and Exposures
The following subparagraphs provide additional information to assist
the reader in using the Respirator Selection Logic Sequence.
Subparagraph 1: Oxygen-Deficient
Atmosphere
NIOSH defines an oxygen-deficient atmosphere as any atmosphere
containing oxygen at a concentration below 19.5% at sea level. NIOSH
certification of supplied-air or air-purifying respirators is limited
to those respirators used in atmospheres containing at least 19.5%
oxygen, except for those supplied-air respirators equipped with
auxiliary self-contained breathing apparatus (SCBA).
The minimum requirement of 19.5% oxygen at sea level provides an
adequate amount of oxygen for most work assignments and includes
a safety factor. The safety factor is needed because oxygen-deficient
atmospheres offer little warning of the danger, and the continuous
measurement of an oxygen-deficient atmosphere is difficult.
At oxygen concentrations below 16% at sea level, decreased mental
effectiveness, visual acuity, and muscular coordination occur. At
oxygen concentrations below 10%, loss of consciousness may occur,
and below 6% oxygen, death will result. Often only mild subjective
changes are noted by individuals exposed to low concentrations of
oxygen, and collapse can occur without warning.
Since oxygen-deficient atmospheres are life-threatening, only the
most reliable respirators are recommended; the most reliable respirators
are the self-contained breathing apparatus or the supplied-air respirators
with auxiliary self-contained units. Because a high protection factor
is not necessary to ensure an adequate supply of oxygen even in
an atmosphere containing no oxygen, any certified self-contained
unit is adequate. All aspects of a respiratory protection program
must be instituted for these recommendations to be valid.
Subparagraph 2: Exposure
Limits
The legal, enforceable exposure limit is the permissible exposure
limit (PEL) set by OSHA. NIOSH develops recommended exposure limits
(RELs) for hazardous substances. To formulate these recommendations,
NIOSH evaluates all known available medical, biological and engineering,
chemical trade, and other information relevant to the hazard. Other
exposure limits that can be considered in making respirator selections
include State-OSHA exposure limits (e.g., California), ACGIH TLVs,
AIHA WEELs, corporate exposure limits, etc. The effectiveness of
this RSL is limited to the adequacy of the selected exposure limits
in protecting the health of workers. Exposure limits based on a
thorough evaluation of more recent or extensive data should be given
priority.
For all chemicals that cause irritation or systemic effects but
do not cause carcinogenic effects, it is currently believed that
a threshold exposure concentration exists such that virtually all
persons in the working population (with the possible exception of
hypersensitive individuals) would experience no adverse health effects.
Other variables such as the specific situation, worker, or job
may influence the selection of the appropriate exposure limit for
a given contaminant. For example, the effects of some hazardous
substances may be increased due to exposure to other contaminants
present in the workplace or the general environment or to medications
or personal habits of the worker. Such factors, which would affect
the toxicity of a contaminant, would not have been considered in
the determination of the specific exposure limit. Also, some substances
are absorbed by direct contact with the skin and mucous membranes,
thus potentially increasing the total exposure.
Subparagraph 3: Immediately
Dangerous to Life or Health (IDLH)
An IDLH exposure condition is one that poses a threat of exposure
to airborne contaminants when that exposure is likely to cause death
or immediate or delayed permanent adverse health effects or prevent
escape from such an environment. The purpose of establishing an
IDLH exposure level is to ensure that the worker can escape from
a given contaminated environment in the event of failure of the
respiratory protection equipment. The IDLH is considered a maximum
level above which only a highly reliable breathing apparatus providing
maximum worker protection is permitted. Any appropriate approved
respirator may be used to its maximum use concentration up to the
IDLH concentration.
In establishing the IDLH concentration, the following conditions
must be assured:
a. The ability to escape without loss of life
or immediate or delayed irreversible health effects. (Thirty minutes
is considered the maximum time for escape so as to provide some
margin of safety in calculating the IDLH.)
b. The prevention of severe eye or respiratory
irritation or other reactions that would hinder escape.
Sources of information for determining whether the exposure limit
for a contaminant represents an IDLH condition are as follows:
a. Specific IDLH guidelines provided in the literature
such as the NIOSH Pocket Guide for Hazardous Chemical Substances
(http://www.cdc.gov/niosh/npg/npg.html)
and the American Industrial Hygiene Association (AIHA) Hygienic
Guides.
b. Human exposure and effects data, and/or
c. Animal exposure and effects data, and/or
d. Where such data specific to the contaminant
are lacking, toxicologic data from analogous substances and chronic
animal exposure data may be considered.
Subparagraph 4: Eye Irritation
Eye protection in the form of respirators with full facepieces,
helmets, or hoods is required for routine exposures to airborne
contaminants that cause any irritation to the mucous membranes of
the conjunctivae or the cornea or cause any reflex tearing. Eye
protection is required for contaminants that cause minor subjective
effects as well as for those that cause any damage, including disintegration
and sloughing of conjunctival or corneal epithelium, edema, or ulceration.
NIOSH is not aware of any standards for gas-tight goggles that would
permit NIOSH to recommend such goggles as providing adequate eye
protection.
For escape, some eye irritation is permissible if the severity
of irritation does not inhibit the escape and if no irreversible
scarring or ulceration of the eyes or conjunctivae is likely.
When data on threshold levels for eye irritation are insufficient,
quarter or half-mask respirators can be used, provided that the
worker experiences no eye discomfort and no pathologic eye effects
develop. Workers should be told that if any eye discomfort is experienced,
they will be provided with respirators that have full facepieces,
helmets, or hoods and that provide protection equivalent to the
quarter- or half-mask respirators.
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