EH Terminology
Presented by QBE
Loss Control Services
Concentration Units
• ppm- parts of contaminant per million
parts of air by volume.
• ppb- parts of contaminant per billion parts
of air by volume.
• mg/m3- milligrams per cubic meter of air.
• g/m3- micrograms per cubic meter of air.
• f/cc- fibers of contaminant per cubic
meter of air.
Parts Per Million (ppm)
• Used for gases and vapors
• Conversion to mg/m3=
(molecular weight)(ppm)
24.45*
*24.45 conversion factor at 25°C and 1
atmosphere (760 mm) atmospheric
pressure.
Milligrams per Cubic Meter (mg/m3)
• Used for aerosols
• If used for vapors or gases, conversion to
ppm= (mg/m3)(24.45*)
molecular weight
*24.45 conversion factor at 25°C and 1
atmosphere (760 mm) atmospheric
pressure.
Fibers per cubic centimeter (f/cc)
Used for fibrous materials such as asbestos
and fiberglass where the length and width of
the individual fibers are important toxicity
factors.
Other Conversion Factors and Definitions
•
•
•
•
mg- milligram -1/1,000 of a gram
g- microgram -1/1,000,000 of a gram
1000 ppb = 1 ppm
1 ppm = 0.0001%
Exposure Limits
• Time Weighted Average (TWA)- Average
concentration of a substance over an 8-hour
shift, for a 40-hour week, unless otherwise
noted.
• Short Term Exposure Limit (STEL)- 15 minute
TWA exposure that should not be exceeded
more than 4 times per 8 hour shift, separated by
at least 60 minutes between exposures.
Exposure Limits
• Ceiling Limits- The maximum allowable
airborne concentration that should never be
exceeded even momentarily.
• Skin Designation- Indicates that the
substance may be readily absorbed through
the skin, mucous membranes and eyes in
significant amounts and that air sampling
alone may underestimate the overall
exposure.
TWA Calculations
TWA=(C1T1+ C2T2+C3T3+…. CnTn)
T1+ T2+T3+….Tn
Where Cn is the concentration during any
time Tn .
TWA Example
If an employee has an exposure to 25
ppm of acetone for 180 minutes and 10
ppm for 240 minutes, the TWA exposure
=
(25)(180)+(10)(240) =16.4 ppm
180 +240
Exposure Limits
• OSHA (Occupational Safety and Health
Administration)
• NIOSH (National Institute of Occupational Safety
and Health)
• ACGIH (American Conference of Governmental
Industrial Hygienists)
• AIHA (American Industrial Hygiene Association)
• Other- Manufacturer’s Recommended Limits
OSHA
• Permissible Exposure Limits (PELs)
• From table Z-1-A in 29 CFR 1910.1000 or
1926.55 Appendix A for construction.
• A concentration of airborne contaminant that it
is believed nearly all workers may be exposed
to, day after day, on an 8-hour time weighted
average basis, without adverse health effects.
ACGIH
• Threshold Limit Values- (TLVs)
• The concentrations to which it is believed
nearly all employees can be exposed to
without adverse health effects.
NIOSH
• Recommended Exposure Limits (RELs)
• A recommended TWA exposure limit for
up to 10-hour shifts for a 40-hour work
week.
• Usually the most conservative exposure
limits.
AIHA
• Workplace Environmental Exposure
Levels (WEELs)
• Exposure limits developed by the AIHA
for agents with no current exposure limits
established by other organizations.
OSHA vs ACGIH, NIOSH and AIHA
• OSHA’s PELs are legal limits for citation
purposes.
• In many instances PELs are outdated with
current toxicological data by 40 years.
• ACGIH, NIOSH and AIHA update exposure
limits regularly based on most current
toxicology.
• Complying with PELs will not necessarily
prevent occupational diseases.
Mixture TLVs
• Used to evaluate exposure to multiple chemicals
with similar health effects (additive effects).
Mixture TLV=
C1 + C2 + C3 +…….Cn
TLV1 TLV2 TLV3
TLVn
Where Cn is the concentration of a substance and
TLVn is its exposure limit.
• If the mixture TLV exceeds “1”, an overexposure to
the combined chemicals exists.
Mixture TLVs
Example: An employee has a TWA exposure
of 400 ppm to acetone (500 ppm TLV) and to
100 ppm MEK (200 ppm TLV).
Mixture TLV = 400 + 100
500 200
= 0.8 + 0.5
= 1.3 so there is an overexposure
Particle Size
• Inhalable Particulate Mass- Hazardous when
deposited anywhere in the respiratory tract (<100
µm).
• Thoracic Particulate Mass- Hazardous when
deposited in the airways and gas exchange region
(<25 µm).
• Respirable Particulate Mass- Hazardous when
deposited in the gas exchange region (<10 µm).
Conclusion
If you don’t understand an
industrial hygiene report, don’t
be afraid to ask questions.