Health hazards are caused by any chemical or biological exposure that interacts adversely with organs within our body, causing illnesses or injuries. The majority of chemical exposures result from inhaling chemical contaminants in the form of vapors, gases, dusts, fumes, and mists, or from skin absorption of these materials. The degree of the hazard depends on the length of exposure time and the amount or quantity of the chemical agent. This is considered to be the dose of a substance. A chemical is considered a poison when it causes harmful effects or interferes with biological reactions in the body. Only those chemicals that are associated with a great risk of harmful effects are designated as poisons.
Dose is the most important factor determining whether or not someone will have an adverse effect from a chemical exposure. The longer someone works at a job and the more chemical agent that gets into the air or on the skin, the higher the dose potential. Two components that make up dose are as follows:
- • The length of exposure, or how long someone is exposed—1 hour, 1 day, 1 year,
- 10 years, etc.
- • The quantity of substance in the air (concentration), how much someone gets on the skin or breathes into the lungs, and/or the amount eaten or ingested.
Another important factor to consider about the dose is the relationship of two or more chemicals acting together that cause an increased risk to the body. This interaction of chemicals that multiply the chance of harmful effects is called a synergistic effect. Many chemicals can interact, and although the dose of any one chemical may be too low to affect someone, the combination of doses from different chemicals may be harmful. For example, the combination of chemical exposures and a personal habit such as cigarette smoking may be more harmful than just an exposure to one chemical. The combination of smoking and exposure to asbestos increases the chance of lung cancer by as much as 50 times.
The type and severity of the body's response is related to the dose and the nature of the specific contaminant present. Air that looks dirty or has an offensive odor may, in fact, pose no threat whatsoever to the tissues of the respiratory system. In contrast, some gases that are odorless, or at least not offensive, can cause severe tissue damage. Particles that normally cause lung damage can't even be seen. Many times, however, large visible clouds of dust are a good indicator that smaller particles may also be present.
The body is a complicated collection of cells, tissues, and organs having special ways of protecting itself against harm. These are usually called the body's defense systems. The body's defense systems can be broken down, overcome, or bypassed. When this happens, injury or illness can result. Sometimes, job-related injuries or illness are temporary, and someone can recover completely. Other times, as in the case of chronic lung diseases like silicosis or cancer, these are permanent changes that may lead to death.