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Appendix D - Training Program
Occupational Exposure Limits
Objectives/Samples of Behavior:
Explain what OELs are and their possible sources.
Distinguish among TWAs, STELs, ceiling limits, skin notations, and IDLH limits.
Identify what to do when OELs are exceeded.
A. Sources
Air Force Occupation Safety and Health (AFOSH) Standard 48-8 OELs
Limits enforceable
Appendices for specific substances - lead, hydrazine, etc.
Occupation Safety & Health Administration (OSHA) Permissible Exposure Limits (PELs)
Found in 29 CFR 1910 (Subpart Z)
Legal lijmits for restricting worker exposures
American Conference of Governmental Industrial Hygieneists (ACGIH) Threshold Limit Values (TLVs)
ACGIH TLV booklet
Instrial hygiene guidelines
Limits enforceable by the Air Force
National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limits (REL)
NIOSH Pocket Guide
Usually not enforceable
Ultraconservative in some cases
B. Definitions and Restrictions
Air Force occupational exposure limits
OELS are the most stringent of:
AFOSH Standard values
OSHA PELs
ACGIH TLVs
NIOSH RELs
Published exposure limits (only according to 29 CFR 1910.120)
If no OSHA PEL exists and the operation is covered under HAZWOPER, the published exposure level is the NIOSH REL.
If no NIOSH REL, the published exposure limit is the ACGIH TLV
Air Force emergency exposure guidelines
These are NOT occupational exposure guidelines; they are for public exposure during emergency situations
These guidelines are discussed in AFOSH Standard 48-8
Sources:
National Academy of Sciences (NAS) - prpeferred limits - SPEGLS / EEGLs - Short-term Public Emergency Exposure Guidelines and Emergency Exposure Guidelines
American Industrial Hygiene Association - when no SPEGL / EEGL available - ERPG - Emergency Response Planning Guidelines
Last choice for emergency evacuation of personnel: ACGIH TLVs and OSHA PELs
OEL restrictions
OELs do not apply to evaluations of:
Community air pollution
Continuous exposures
Hypersensitive personnel
Protection of the fetus
Protection of mother's milk
ACGIH TLV definition: Airborne concentration of substances representing conditions under which it is believed that nearly all workers may be exposed day after day without adverse effects.
ACGIH TLV restrictions:
Only covers the majority of workers
Cannot determine safe vs unsafe conditions
Does not prove or disprove disease
Does not establish relative index of toxicity
Adverse effects include health impairment, irritation, nuisance, narcosis and stress
Not for working conditions different from those in the United States
IDLH - immediately dangerous to life or health
NIOSH definition: the maximum concentration from which, in the event of respiratory protection failure, one could escape without experiencing any escape-impairing (e.g. severe eye irritation) or irreversible health effects.
OSHA definition: any condition that poses an immediate or delayed threat to life or health that would cause irreversible adverse health effects or interfere with an individual's ability to escape.
IDLH concentrations are found in NIOSH pocket guide
Only purpose is respirator selection
MUST wear SCBA to ENTER an IDLH atmosphere
OEL concentrations - units of measure
Gases and vapors. There is a conversion factor which may be used to convert mg/m3 to ppm. Either unit may be used.
Milligrams per cubic meter (mg/m3)
Parts per million (ppm)
Aerosols
Milligrams per cubic meter (mg/m3)
Fibers per cubic centimeter (asbestos only at this point)
C. Types of OELs
Time-weighted average (8-hr OEL-TWA & TLV-TWA)
Based on an 8 hr work day, 40 hr week
Usually based on chronic exposures
Calculate an average worker's daily exposures using the equation:
TWA = (C1T1 + C2T2 + ... CnTn) / (8 hours)
Short term exposure limit (OEL-STEL & TLV-STEL)
Based on acute effects
ACGIH/AFOSH Std definition: a 15 minute time-weighted average exposure which must not be exceeded during the workday
Exposures above the TLV-TWA up to the STEL should not be longer than 15 minutes and should not occur more than 4 times per day
There should be at least 60 minutes bnetween successive exposures in this range
The 8-hr TWA must not be exceeded
Ceiling limit (OEL-C & TLV-C)
For substances which are fast-acting - often for irritants
A concentration which must be exceeded, even instantaneously, at any time during the workday
OSHA ceilings are different - "C" notation vs "acceptable ceiling concentration"
Excursion limits
For substances with OEL-TWA values but no STEL or ceiling
Excursions at levels up to three times the OEL-TWA are allowed for no more than a total of 30 minutes per workday
Levels should never exceed five times the OEL-TWA
The daily OEL-TWZ must not be exceeded
"Skin" notation
Chemical vapor or liquid may be absorbed through intact skin
Contributes to the overall dose
Inhalation + skin absorption = greater dose than air sampling indicates
OELs based ONLY on inhalation
Therefore, OEL may be invalidated for a chemical with a skin notation
D. What to do when OELs are exceeded - do something to reduce exposure below the OEL
Substitution best but not always practical
Recommend controls to lower exposure
Engineering controls
Administrative controls / work practices
PPE (respiratory protection)
E. Only trained / knowledgeable / experienced personnel should interpret air sampling results
BEE personnel, industrial hygienists & technicians, etc.
For contractors, this should be done by industrial hygienists