A MISUNDERSTANDING
This column is about partial truth: Most believe that a lowerexposure limit means a chemical is more toxic, and should be avoided for justthat reason. That analysisis partially true.

But some chemicals that aren’t terribly hazardous, or suspected or proven to be carcinogenic, have low exposure limits. That possibly surprising observation is completely true.

WHAT ARE EXPOSURE LIMITS?
An exposure limit is an estimate of an amount of dermal (skin) contact, ingested volume, and inhaled concentration. Almost always the exposure limit for solvents involves inhalation.

REVERSIBLE DAMAGE
Exposure limits represent exposure which workers can sustain without reversible damage. It is the aim, when exposure limits are set, to avoid any permanent human damage. In other words, exposure limits are not estimates of exposure which workers can sustain without any damage. Surprised? Yes, workers compliant with exposure limits in your shop can be damaged with chemical exposure. One should expect some concern by their workers after exposure but the harmful effect should be reversible.

SPECIAL POPULATIONS
Exposure limits do not generally apply to persons with known human differences of age, sex, weight, heredity, race, or sensitivity to chemicals (such as contact dermatitis). Surprised? Most persons think exposure limits compensate for such differences, but they don’t. They don’t because the effects can be so broadly different from one person to another, even among those who aren’t in “special populations.” For example, if I have contact dermatitis, dermal exposure limits don’t describe the hazards I face.

WHAT IS COVERED?
Exposure limits cover:

• Both acute (short-term period between exposure and onset of symptoms) and chronic (long-time period between exposure to an agent and the onset of symptoms) types of exposure.
• Consequences spanning nasal or dermal irritation to birth defects, kidney or heart failure, and even death.
• The possibly unknown slope of the dose-response curve. Surely you’re not surprised that exposure limits produce controversy when they are set?

“NA” CAN’T BE ALL BAD, CAN IT?
Corporations producing chemicals are whipsawed. If their proposed exposure limit (CEL, AEL, CGL) is quite low, they can suffer the shortterm and potentially fatal pain of a low sales rate. If the proposed limit is quite high, they can suffer the long-term pain of harming people and the likely fatal pain of defending lawsuits about that. Juxtaposing these two issues should and usually does create a balanced attitude.

But some corporations have been known to avoid the discipline of achieving this balance by not proposing an exposure limit. These suppliers write “NA” on the MSDS where the exposure limit is called for. Managers considering use of this chemical for any purpose should seek another chemical from another manufacturer.