Section: 16 | Threshold Limits for Airborne Contaminants |

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THRESHOLD LIMITS FOR AIRBORNE CONTAMINANTS

Several organizations recommend limits of exposure to airborne contaminants in the workplace. These include the United States National Institute for Occupational Safety and Health (NIOSH)-recommended exposure limits (RELs), which are intended to limit exposure to hazardous substances in workplace air to protect workers, and the non-governmental organization, American Conference of Governmental Industrial Hygienists (ACGIH). Threshold Limit Values (TLVs^®) are the airborne concentrations of chemical substances under which it is believed that nearly all workers may be repeatedly exposed, day after day, over a working lifetime, without adverse effects.

In contrast to the ACGIH- and NIOSH-recommended limits of exposure, the United States Occupational Safety and Health Administration (OSHA) has established legal occupational exposure limits known as permissible exposure limits (PELs) which are based on a consideration of factors in addition to the adverse effects associated with airborne contaminants. When establishing PELs, OSHA takes into account technical feasibility and economic considerations for employers in addition to the adverse effects associated with the airborne contaminant. While these PELs are legal exposure limits, OSHA recognizes that many of its PELs are outdated and inadequate for ensuring protection of worker health. Most of OSHA’s PELs were issued shortly after adoption of the Occupational Safety and Health (OSH) Act in 1970 and have not been updated since that time. OSHA has stated that alternate occupational exposure limits such as NIOSH RELs and ACGIH TLVs may serve to better protect workers.

The following table gives threshold limit values for substances that may be encountered in the atmosphere of a chemical laboratory or industrial facility. The table includes NIOSH RELs and ACGIH TLVs, but not OSHA PELs given OSHA’s caution about PELs.

NIOSH RELs and the ACGIH TLVs are given in two forms:

Time-weighted average (TWA) concentration for a normal 8-hr workday and 40-hr workweek.
Short-term exposure limit (STEL), which should not be exceeded for more than 15 minutes.

All values refer to the concentration in air at 25 °C and normal atmospheric pressure. Data for gases are given in parts per million by volume (ppm). Values for liquids refer to mists or aerosols, and those for solids to dusts or fumes; both are stated in mass concentration units (mg/m³). In some cases, a “Ceiling value” is provided which indicates a ceiling limit that should not be exceeded even for very brief periods because of acute toxic effects of the substance. The notation “levels as low as possible” in the Comments column indicates such a high degree of hazard that no safe limit can be recommended. Expressions such as "inhalable fraction and vapor" and "inhalable particulate matter" that appear after a TLV indicate that the TLV value has been adjusted to reflect the influence of particle size on the respiratory hazard. See Refs. 1-3 for details.

Substances are listed alphabetically by systematic name. Synonyms are also provided. The Comments provide further information on the physical form of the substance and the basis to which the limit is referred. The Formula column gives the molecular formula in the Hill convention for organic compounds and the customary line formula for inorganic compounds. The ACGIH and NIOSH TWA, STEL and Ceiling limit are provided if available for a substance.

Note that the entries in this table are for substances that have undesirable physiological effects on humans. Many other substances should be avoided in the workplace because of explosion or asphyxia hazards.

References

2018 TLVs and BEIs, American Conference of Governmental Industrial Hygienists, 1330 Kemper Meadow Drive, Cincinnati, OH 45240-1634, 2018 <www.acgih.org>.
NIOSH Pocket Guide to Chemical Hazards, U.S. Department of Health and Human Services, National Institute for Occupational Health and Safety, 2016 <www.cdc.gov/niosh/npg/>.
OSHA Annotated PELs, TABLE Z-1, U.S. Department of Labor, Occupational Safety and Health Administration, 2017 <www.osha.gov/dsg/annotated-pels/tablez-1.html>.

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Threshold Limits for Airborne Contaminants

Name	Comments	Formula	CAS Reg. No.	Mol. wt.	ACGIH Time-weighted average	ACGIH Short-term exposure limit	ACGIH Ceiling	NIOSH Time-weighted average	NIOSH Short-term exposure limit	NIOSH Ceiling	Basis
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Abate	[Temephos]	C₁₆H₂₀O₆P₂S₃	3383-96-8	466.469	1 mg/m³			10 mg/m³ (total); 5 mg/m³ (resp)			Cholinesterase inhibitor
Acetaldehyde	[Ethanal]	CH₃CHO	75-07-0	44.052			25 ppm				Eye and upper respiratory tract irritation
Acetamide		CH₃CONH₂	60-35-5	59.067	1 ppm (inhalable fraction and vapor)						Liver cancer and damage
Acetic acid	[Ethanoic acid]	CH₃COOH	64-19-7	60.052	10 ppm	15 ppm		10 ppm	15 ppm		Upper respiratory tract and eye irritation; pulmonary function
Acetic anhydride	[Acetyl acetate]	C₄H₆O₃	108-24-7	102.089	1 ppm	3 ppm				5 ppm	Eye and upper respiratory tract irritation
Acetone	[2-Propanone]	(CH₃)₂CO	67-64-1	58.079	250 ppm	500 ppm		250 ppm			Eye and upper respiratory tract irritation; central nervous system impairment
Acetone cyanohydrin	as CN	C₄H₇NO	75-86-5	85.105			5 mg/m³			4 mg/m³ (1 ppm) [15-minute]	Upper respiratory tract irritation; headache; hypoxia/cyanosis
Acetonitrile	[Methyl cyanide]	CH₃CN	75-05-8	41.052	20 ppm			20 ppm			Lower respiratory tract irritation
Acetophenone	[Methyl phenyl ketone]	C₆H₅C=OCH₃	98-86-2	120.149	10 ppm						Upper respiratory tract irritation; central nervous system impairment; pregnancy loss
2-(Acetyloxy)benzoic acid	[Acetylsalicylic acid (Aspirin)]	C₉H₈O₄	50-78-2	180.158	5 mg/m³			5 mg/m³			Skin and eye irritation
Acrolein	[2-Propenal]	CH₂=CHCHO	107-02-8	56.063			0.1 ppm	0.1 ppm		0.3 ppm	Eye and upper respiratory tract irritation; pulmonary edema; pulmonary emphysema
Acrylamide	[2-Propenamide]	C₃H₅NO	79-06-1	71.078	0.03 mg/m³ (inhalable fraction and vapor)			0.03 mg/m³			Central nervous system impairment
Acrylic acid	[2-Propenoic acid]	C₃H₄O₂	79-10-7	72.063	2 ppm			2 ppm			Upper respiratory tract irritation
Acrylonitrile	[Propenenitrile]	CH₂=CHCN	107-13-1	53.063	2 ppm			1 ppm		10 ppm [15-minute]	Upper respiratory tract irritation
Alachlor	[Acetamide, 2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)-]	C₁₄H₂₀ClNO₂	15972-60-8	269.768	1 mg/m³ (inhalable fraction and vapor)						Hemosiderosis (liver, spleen, kidney)
Aldrin		C₁₂H₈Cl₆	309-00-2	364.910	0.05 mg/m³ (inhalable fraction and vapor)			0.25 mg/m³			Central nervous system impairment; liver and kidney damage
Allyl alcohol	[2-Propen-1-ol]	C₃H₆O	107-18-6	58.079	0.5 ppm			2 ppm	4 ppm		Eye and upper respiratory tract irritation
Allyl glycidyl ether	[AGE]	C₆H₁₀O₂	106-92-3	114.142	1 ppm			5 ppm	10 ppm		Upper respiratory tract irritation; eye and skin irritation; dermatitis
Allyl propyl disulfide		C₆H₁₂S₂	2179-59-1	148.289	0.5 ppm			2 ppm	3 ppm		Upper respiratory tract and eye irritation

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