1. STANDARDS FOR EXPOSURE TO AIRBORNE CONTAMINANTS
Yves Alarie, Ph.D
Professor Emeritus
University of
Pittsburgh,USA

2. A. STANDARDS OR GUIDELINES
A variety of standards have been promulgated. Some are Federal standards, while others are guidelines promulgated by different groups.
Table 18 provides a summary and the definition
of the most important.
a) National Ambient Air Quality Standards (NAAQS).
Established by EPA, following a review of the literature on a particular substance. The review is published as an "Air Quality Criteria Document" and readily available in libraries. The current NAAQS are listed in Table 19.

3. b) Threshold Limit Values (TLV); Biological Exposure Indices (BEI).
These are established by the American Conference of Governmental Industrial Hygienists (ACGIH) which was established in It started issuing exposure guidelines in 1946 for a small number of industrial chemicals and there is a TLV for about 600 industrial chemicals. Each year it published a booklet (1) listing those values. This booklet is available from:
Executive Secretary
ACGIH
6500 Glenway Avenue, Building D-7
Cincinnati, Ohio
1. ACGIH Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices.

4. More recently the ACGIH has introduced Biological Exposure Indices (BEIs) as reference values intended as guidelines for evaluation of potential health hazards in the practice of industrial hygiene. These, unlike TLVs which refer to an air concentration, are for amount of the chemical or its metabolite in blood, urine, exhaled air, etc. There are 34 established and/or proposed BEIs.

5. Both TLVs and BEIs are established after a literature review, much more extensive for BEIs than for TLVs and this review is published.66 In this publication you can find the basis for establishing a TLV or BEI. Many TLVs have been recently reviewed and much more extensive documentation is now available. Also there have been obvious changes over the years as to what the committee members regard as an “adverse health effect” and what "most workers" means. Twenty years ago "most workers” was about 85%. Now I don't know.
66ACGIH. Documentation of the Threshold Limit Values and Biological Exposure Indices.

6. It should be kept in mind that these values are guidelines, developed initially for Normal, Healthy, Adult, Male, not female and certainly not pregnant females.
Before you can use these values you should read the "Preface" which is now 10 pages long in the booklet. Also you should read the Documentation for each substance that you are interested in.

7. c) Permissible Exposure Limit ( PEL).
These are established by the Occupational Safety and Health Administration (OSHA). They are THE LAW.
In 1970, OSHA used the TLVs values published in 1968 by the ACGIH and made those values PELs.

8. In 1989, OSHA revised its list of PEL by adopting the ACGIH TLVs with a few exceptions. You can obtain these from:
"NIOSH Pocket Guide to Chemical Hazards, June 1990"67. This publication contains a variety of other information for all the listed chemicals and is very useful to have, or as reprinted68. However, this revision was challenged in court and reversed.
See Table 18.
67For Sale by Superintendent of Documents, U.S. Government Printing Office, Washington, DC, or at the Federal Building in your city.
68Air Contaminants - Permissible Exposure Limits (Title 29 Code of Federal Regulations, Part ), Applied Industrial Hygiene 4, F22-R-19, 1989.

9. d) Recommended Exposure Level (REL).
The National Institute of Occupational Safety and Health (NIOSH) develop these for the workplace and transmits them to OSHA and the Mine Safety and Health Administration (MSHA) for use in promulgating legal standards i.e., PEL. For each chemical there is a "Criteria for a Recommended Standard" document. There are about 120 of these documents available in libraries. They are a good source of information, not only on the toxicity of the chemical but also work practices, medical surveillance, protective equipment, etc. Unfortunately they are now out of date.

10. e) Air Toxics.
These are more recent and established by each State. They are ambient air criteria for the general population. A variety of approaches have been taken. A popular one is to take the PEL and divide it by some factor to take into account the fact that the general population would be exposed 24 hrs/day and 7 days/week instead of the PEL or TLV which is for 8 hrs/day and 5 days/week. Then you can throw in some safety factors of 10 and another safety factor of 10 if there is any rumor that one rat somewhere got cancer. You end up with a number. Nonsense.

11. a) Types of Data. - Human exposures, on the job
B. ESTABLISHING A TLV OR PEL
a) Types of Data.
There is no established protocol to develop a TLV or PEL. The types of data assembled to arrive at a decision will include the following:
- Human exposures, laboratory experiments
- Human exposures, on the job
- Human exposures, accidental exposures
- Animal exposures
- Reports from health professionals, i.e. physicians, nurses, industrial hygienists
- Reports from chemists and chemical engineers concerning a variety of elements for the chemical being produced or used
TLVs are under continuous review and can be changed after publication of "Notice of Intended Change" and a comment period. PEL can also be changed but this is a slower process since this is the law. However, as new data are accumulated they are considered and changes are made.

12. b) Types of Effect. i) Health Hazard
Any type of toxicological effect can be considered to establish a TLV or PEL. A review of the Documentation for TLV and the Lecture Notes of Dr. H. F. Smyth Jr. of the University of Pittsburgh was undertaken by OSHA to get an idea of the major health hazard categories used to establish TLVs. These are given in the Table. As you can see there are large differences, from nauseating odor to cancer. Therefore, when you see that a TLV for X is 10 ppm and a TLV for Y is 100 ppm don't conclude that X is 10 times more toxic than Y. This is the worst mistake you can make.

13. ii) "Good Housekeeping"
- No TLV above 10 mg/m3 for any aerosol, including "nuisance or inert dust”
- No TLV above 1,000 ppm for gases or vapors, except for CO2 (TLV = 5,000 ppm) or for simple asphyxiants which are permitted up to 3% (reduction of O2 content to 18%) at sea level pressure (760 mmHg) or to an equivalent partial pressure of O2 of 135 mmHg.