Chemical Exposure Hazards

When we discuss the hazards of chemical exposure we are really speaking about chemical toxicology, Let's quickly review some of the terms and definitions relating to hazardous chemical materials. TOXICOLOGY is the study of toxic or poisonous substances. It relates to the physiological effect, source, symptoms and remedial measures for the materials. A TOXIN is any substance, which upon contact with a living organism, can cause injury or interference with the life processes of that organism, without acting mechanically. TOXICITY is the amount of a toxin or poison which under specified conditions will result in detrimental biological changes.

Chemical toxins cause injury in relatively small amounts compared to other substances, but materials classified as toxic may differ by a small factor or ten billion in the potencies. The margin of safety is determined by the dosage and the toxicity of the material encountered.

DOSE is the quantity of a chemical substance that enters into the biological system. Dose is not synonymous with concentration.

CONCENTRATION is the quantity of a chemical substance that is exposed externally to a biological system.

UNITS OF DOSE AND CONCENTRATION can be expressed in terms of the quantity administered, such as per unit weight, usually expressed as milligrams of a chemical substance per kilogram of body mass. It can also be expressed per area of skin surface, unit volume of air inhaled, which is commonly termed parts per million of air by volume. This term parts per million is very important, as you'll see this term more often than any other. It can be explained very simply. Let's take a bottle, which contains one million parts of air. Drop in a chemical substance of 10 parts into this air space and you have 10 parts of the substance, per million parts of air, by volume. Another way to look at parts per million is eleven parts million is equivalent to 11 minutes in two years. Or an eleven ounce needle in a ton of hay. One part per million is equal to one bottle of soda in a row of bottles over 40 miles long. One car in a line of traffic 2,650 miles long. One part per billion equates to one quarter, in a stack of quarters nearly 1,500 miles high. One part per trillion is equal to one minute of time in the past one million, 920 thousand years. These are certainly not scientific explanations, but it does put the concept into perspective, for ease of understanding what parts per million means. We can now measure parts per billion, or parts per trillion. Each chemical is different, with different concentrations of hazards. Identifying by parts per million or billion is just one method of protecting individuals from potential health hazards.

ACUTE TOXICITY is the toxicity resulting from exposure to a relatively high concentration of a toxic chemical material over a relatively short period of time, such as seconds, minutes or hours. The relationship of exposure and toxic effect is usually quite clear and defined, since the effect is relatively immediately. Acute means quick.

CHRONIC TOXICITY is the toxicity resulting from exposure to a relatively low concentration of a toxic chemical material over a long period of time, such as days, weeks, months or years. With chronic exposure, the relationship between exposure and toxic effect is not always apparent and in some cases cannot be established with certainty. Acute toxicity is immediately known, such as a person passes out immediately from the effect. Chronic toxicity could go for several months or years before feeling the effects of the exposure.
Ok, let's take a look at some factors which may modify the toxic effects of a substance:

1. Chemical route of exposure or entry. Was it inhaled, absorbed through the skin or ingested?

2. The physical state of the substance. Was it solid, liquid, gas? What was the concentration of the substance?

3. The external temperature. Some chemical materials are more toxic or hazardous when they are warm, than others.

4. The physiological condition of the individual. Was the person in good health or was the person in poor health. Persons in good health are more likely to recover more quickly than persons in poor health. A good way to describe the various toxicants is by their actions on living organisms, such as irritants, asphyxiants, nerve poisons or systemic poisons.

5. The dosage. This again, goes back to the amount or concentration of the substance. Was it 10 parts per million, or 500 parts per million. The higher the dose, the more toxic it may be.

Most toxic effects are reversible and do not cause permanent damage, although complete recovery may take a long time. With regard to emergency response personnel, potential acute exposures are more typical. Acute exposures do not persist for long periods of time. Acute skin exposures may occur when workers must work close to substances in order to control a release or contain and treat the spilled material. Once the immediate site problems have been alleviated, exposures tend to become more chronic in nature as cleanup progresses.

Chronic exposures usually are associated more with hazardous waste site investigations where contaminated soil, debris and water or containment systems may hold diluted chemicals. Abandoned waste sites represent potential chronic exposure problems. However, during initial activities at these sites, personnel engaged in sampling, handling containers, or bulking compatible liquids face an increased risk of acute exposures to splashes, mists, gasses or particulates.

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Threshold Limit Value. TLV's were developed based on the BODY's ABILITY TO WITHSTAND VARIOUS INSULTS AND CONTINUE TO RECOVER UNTIL A LEVEL IS REACHED WHERE RECOVERY WILL NO LONGER OCCUR, or occur at decreased rates. In other words, there is a sufficiently small amount of exposure to toxic substances that does nothing injurious. This concept implies that a threshold of effect or a "no effect" level exists. This no-effect level will vary from chemical to chemical. TLV's refer to airborne concentrations of substances and represent conditions under which it is believed that nearly all workers may be repeatedly exposed, day after day, without adverse effect. When you look at the information on Material Safety Data Sheets, or other technical information about a particular hazardous substance or chemical, TLV's will most often be listed. You have to be able to understand this information to protect yourselves from the toxic effect of the substance. Part of the information you need to know is the Measures of TLV's.

TIME WEIGHTED AVERAGE is the concentration most workers can be repeatedly exposed to during an 8 hour day, 40 hour work week without developing adverse acute or chronic effect. A TLV may have a TLV with a SKIN notation. This special "skin" notation indicates that direct skin contact should be avoided due to the chemical's skin absorption properties.

TLV-C or Ceiling. A TLV-C is a ceiling value. It's the concentration that cannot be exceeded even instantaneously because of serious health effects.

TLV-STEL or Short Term Exposure Level is the allowable exposure concentration for a short period of time. A 15 minute average exposure period, repeated no more than four times a day, with at least one hour between successive exposures, provided the 8 hour Time Weighted Average is not exceeded. If you follow these guidelines, there should be no health problem.

If you see the term IDLH, it's time to be especially careful. The term IDLH means Immediate Dangerous to Life and Health. IDLH means conditions that pose an immediate threat to life or health or conditions that pose an immediate threat of severe exposure to contaminants. Exposure to IDLH environments is likely to cause irreversible damage or death.

The world of toxicology is so technical and complex that only highly educated and trained personnel fully understand the hundreds and thousands of terms and definitions. It's difficult to know all the toxic effects of thousands of chemicals, their parts per million rating, TLV's, STEL's, and what precautions should be taken when working with hazardous materials. The most common sense advice is to know as much about a particular chemical or hazardous material, that you're working with, or may be exposed to in the event of an emergency.

Read and follow the information contained on Chemical  Material Safety Data Sheets and chemical labels. Ask questions. The more you know about potential hazards, the more prepared you'll be when working with these substances.