1. Chemical Substances TLV® Committee
Lisa Brosseau, ScD, CIH
Associate Professor
University of Minnesota
Chair, TLV®-CS Committee
I’ve been a member of the Threshold Limit Values for Chemical Substances Committee since I was first a member of the Dust and Inorganics Subcommittee, which I then chaired from In 1998 I became chair of the full committee.
My primary goal as chair has been to enhance the work of committee members, by improving their resources, knowledge and inter-personal connections.
My secondary goal has been to enhance the committee’s connections to other OEV groups, in an effort to share information and, ultimately, workload.

2. ACGIH® Committees
Committees consist of members, who volunteer time toward developing scientific guidelines and publications
Primary goal is to serve the scientific needs of occupational hygienists
Committee expenses (travel) are supported by ACGIH®
Time is donated by the members

3. A Short Historical Perspective
1941 TLV® Committee Created
Committee of Technical Standards creates Subcommittee on Threshold Limits (becomes independent committee in 1944)
1946 List Published
First published list of “Maximum Allowable Concentrations” (MACs) for 150 chemical substances (renamed Threshold Limit Values in 1948)
I’d like to start this talk by giving a brief overview of the history of this committee. The TLV Committee came into being 60 years ago, when scientists and policy makers realized there were enough data to recommend “safe” levels of airborne contaminants in the workplace.
The OEV concept arose in Germany in the late 1800s, but it wasn’t until industrial hygienists and toxicologists in the US began to propose OEVs in the 1940s that the concept really took off. The first list of OEVs was published in the Journal of Industrial Hygiene in 1940 by Bowditch et al.--these were guidelines developed by the Massachusetts Public Health Service. The TLV Committee was created the year after this and published its first list of Maximum Allowable Concentrations (MACs) for 150 substances in The name Threshold Limit Value was adopted in 1948.

4. History 1955 Written Documentation
TLV® Committee begins to write Documentation for each TLV® (207 completed by 1958)
Published 1st edition in 1962 (257 substances)
Ten years later, the committee recognized the need for written documentations, in which the key scientific literature was reviewed and the approach used to derive a TLV was explained. It is the written documentations, I believe, that accounts for the committee’s prestige. Without such documentations it is difficult to understand where a particular number comes from.

5. History Important Additions and Changes 1961 - Skin Notation
Carcinogens Appendix
Excursion factors
Notice of Intended Changes
TLVs® for Physical Agents Committee
Cancer classifications defined
Operational guidelines & procedures
List of Substances & Issues Under Study
As the committee improved its decision-making, it recognized the need for identifying other important characteristics about the chemicals it reviewed. Some substances, for example, can be absorbed through the skin, which makes an airborne concentration less relevant to the dose received. The SKIN notation was developed to address this issue. A classification scheme was developed to identify carcinogens, similar to that used by other groups. The committee recognized the need to inform of impending changes--thus, it began to publish proposed TLVs on the Notice of Intended Changes before adopting the final values. A further notification List of Substances and Issues Under Study was later added, to identify those substances which the committee planned to evaluate in the near future.
A second TLV committee concerned with Physical Agents was added in the late 1960s.
And, as with any committee whose work becomes both more complex and far-reaching, the TLV committee created its first set of operational guidelines and procedures in 1980.

6. History
More Changes
Established Biological Exposure Indices (BEI®) Committee
Deleted STELS for many substances
CD-ROM
Reformatted TLV® Book to include information on “TLV® Basis - Critical Effects”
The third TLV committee was added in This committee proposes biological exposure indices.
ACGIH began to publish all of the TLV documentations (including versions published in the past) on a CD-ROM in Other information about OEVs, including the AIHA WEEL values and the NIOSH Pocket Guide, are also listed on this very useful resource.
In 1998, a new column was added to the TLV Booklet, to identify the critical effects for each TLV. These effects were those that formed the basis of the TLV.

7. Committee Structure Chair Vice-Chair, Subcommittee Chairs, Members
Recommendations from Committee & Staff; Board appoints
Vice-Chair, Subcommittee Chairs, Members
Recommended by Chair, appointed by Board
Three Subcommittees, each with Chair
Dusts & Inorganics (D&I)
Hydrogen, Oxygen & Carbon Compounds (HOC)
Miscellaneous Compounds (MISCO)
Staff Support (Liaison, Clerical, Literature Searching)
Now I’d like to spend a short time describing the committee and its structure and makeup.
The committee consists of 3 subcommittees, each of which has a chair. The full committee has a chair, nominated by the ACGIH Board of Directors, and a vice chair, nominated by the chair.
The three subcommittees are organized to divide all of the chemical substances into three roughly equal groups--dusts & inorganics (called D&I), hydrogen/oxygen/and carbon compounds (called HOC), and miscellaneous compounds (called MISCO).

8. Chemical Substance Subcommittees
Approximately 10 members on each
Membership from academia, government, unions, industry
Membership represents four key disciplines:
Industrial Hygiene
Toxicology
Occupational Medicine
Occupational Epidemiology
Each of the three subcommittees has approximately ten members, drawn from academia, government, labor and industry. We attempt to create a balance of disciplines on each subcommittee, drawing from the four most important occupational health professions--industrial hygiene, toxicology, medicine, and epidemiology. We may also seek individuals with specific expertise, for example, respiratory physiology, inhalation toxicology, and carcinogenicity.

9. Other Subcommittees Chemical Selection Membership Notations
Recommendations to HOC, D&I, MISCO
Membership
Recruitment, screening, recommendations
Notations
Definitions, new proposals
Communications
Explaining our decisions
Members of the committee are also expected to participate on at least one other “administrative” subcommittee. We currently have four of these, which are responsible for selecting new chemicals, recruiting and nominating new members, defining and developing notations and classifications, and communicating with our users through educational events and publications.

10. Committee Structure Board of Directors Staff Chair of TLV® Committee
Administrative Subcommittees
(Membership, Chemical Selection)
Steering Committee
The committee chair and vice chair, along with the 3 chairs of the chemical substance subcommittees, comprise a “steering committee,” which oversees all activities, both internal and external. The committee chair is directly responsible to the Board of Directors for the committee’s workplan, budget and accomplishments, but I rely heavily on the steering committee for guidance and implementation.
Dust & Inorganics Subcommittee (D&I)
Hydrogen, Oxygen, Carbon Subcommittee (HOC)
Miscellaneous Compounds Subcommittee
(MISCO)

11. TLV® Development Process
Under Study
List
Draft
Doc.
Committee Review
& Revision
External
Input
Committee Review
& Revision
Committee
& Board
Approval
NIC
Committee
& Board
Approval
Adopted
Value

12. TLVs® Defined TLV® — more than just “THE NUMBER”
Documentation describes:
Critical health effects
Quality of the data relied upon and areas of uncertainty
Possible sensitive subgroups
Type of TLV® (TWA, STEL, C) and reason for selection
Notations
I’d now like to address what is and isn’t a TLV.
As I noted in the historical overview, the TLV is more than just a number. The written documentation reflects a thorough review of the key literature and identifies the critical health effects on which the number is based. It discusses uncertainties, additional routes of entry, and sensitive sub-populations--and addresses some of these with appropriate notations. Without this documentation, the number means little or nothing.

13. Technical, economic, and analytic feasibility are NOT considered
Core TLV® Principles
Focus on airborne exposures in occupational settings
Utilize the “threshold” concept
Primary users are industrial hygienists
Goal is toward protection of “nearly all” workers
While we do not utilize a formal, mathematical risk assessment model, the committee does rely on some core principles.
In particular, we
seek information on airborne exposures and health effects experienced in occupational settings
apply the threshold concept, wherever possible
develop our information toward the sole purpose of assisting industrial hygienists with their work
attempt to protect “nearly all workers” but recognize the possibility of sensitive sub-populations
do not consider technical or economic feasibility, and rarely consider analytic feasibility
Technical, economic, and analytic feasibility are NOT considered

14. The Essential Ingredients for Developing TLVs®
Published / Peer Reviewed Science +
Dedicated Volunteerism
Professional Integrity
& Judgment
And finally, Scott Merkle, the current chair of the ACGIH Board of Directors, best captures the essence of who we are as a committee--high quality scientists who volunteer much time and effort to ensuring professional and honorable decision-making. Somehow this mixture has worked--for over 60 years.

15. Warnings NOT to be used as an index of relative toxicity
NOT for estimating toxic potential of continuous, uninterrupted exposures or other extended work periods
NOT as proof/disproof of existing disease
NOT to evaluate or control air pollution
NOT legal standards
At the front of the TLV booklet we include a list of warnings, which arise from our observations about the abuses and misuses to which TLVs have been subjected.
Specifically, we state that TLVs are:
not to be used as an index of relative toxicity (because the endpoints differ from substance to substance)
not for exposures of work periods other than 8 hr/day
not to prove or disprove an individual’s disease
not to evaluate or control air pollution (which affects people of all ages and for much longer periods of time)
not to be adopted as legal standards
Unfortunately, many groups continue to misuse TLVs...

16. Summary Prefer human over animal data
Use uncertainty factors, if necessary (but no “rules”)
Look for threshold of effects
Consider irritation an important health endpoint
Not concerned with levels of risk
Look for the “worst case” health endpoint
Always select an exposure level
Explain the reasons for our recommendations
So, to summarize, I developed an in exhaustive table of dos and don’ts to describe the kind of work we do:
We prefer human over animal data, use uncertainty factors if necessary (but don’t follow any specific rules), rely on a threshold model, and seek a value that is protective of a variety of endpoints, including irritation (however that is defined).
We don’t use specific levels of risk and we don’t select the same endpoint for every substance. We don’t fail to recommend a TLV for a carcinogen and, hopefully, we never fail to explain how we derived the “number.”