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Toxic Exposure Measuring and Monitoring Chemicals in the Air When toxic chemicals are present in the workplace, your exposure can be estimated by measuring the concentration of a given chemical in the air and the duration of exposure. This measurement is called air or environmental monitoring or sampling and is usually done by industrial hygienists, using various types of instruments.The air is collected from your breathing zone (the air around your nose and mouth) so that the concentrations measured will accurately reflect the concentration you are inhaling. The exposure levels calculated from this monitoring can then be compared to the Permissible Exposure Level for that chemical. Environmental monitoring is the most accurate way to determine your exposure to most chemicals. However, for chemicals that are absorbed by routes other than inhalation, such as through the skin and by ingestion, air monitoring may underestimate the amount of chemical you absorb. For these and some other chemicals, the levels of the chemical (or its breakdown products) in the body can sometimes be measured in the blood, urine or exhaled air. Such testing is called biological monitoring, and the results may give an estimate of the actual dose absorbed into the body. Practical Clues to Exposure Odor: If you smell a chemical, you are inhaling it. However, some chemicals can be smelled at levels well below those that are harmful, so that detecting an odor does not mean that you are inhaling harmful amounts. On the other hand, if you cannot smell a chemical, it may still be present. Some chemicals cannot be smelled even at levels that are harmful. The odor threshold is the lowest level of chemical that can be smelled by most people. If a chemical’s odor threshold is lower than the amount that is hazardous, the chemical is said to have good warning properties. One example is ammonia. Most people can smell it at 5 ppm, below the PEL of 25 ppm. It is important to remember that for most chemicals, the odor thresholds vary widely from person to person. In addition, some chemicals, like hydrogen sulfide, cause you to rapidly lose your ability to smell them (called olfactory fatigue). With these cautions in mind, knowing a chemical’s odor threshold may serve as rough guide to your exposure level. Don’t depend on odor to warn you. Remember that your sense of smell may be better or worse than average, that some very hazardous chemicals have no odor (carbon monoxide), some chemicals of low toxicity have very strong odors (mercaptans added to natural gas), and others produce olfactory fatigue. Taste: If you inhale or ingest a chemical, it may leave a taste in your mouth. Some chemicals have a particular taste, which may be mentioned in an MSDS. Particles in Nose or Mucous: If you cough up mucous (sputum or phlegm) with particles in it, or blow your nose and see particles on your handkerchief, then you have inhaled some chemical in particle form. Unfortunately, most particles which are inhaled into the lungs are too small to see. Settled Dust or Mist: If chemical dust or mist is in the air, it will eventually settle on work surfaces or on your skin, hair and clothing. It is likely that you inhaled some of this chemical while it was in the air. If you or your co-workers experience symptoms known to be caused by a chemical during or shortly after its use, you may have been overexposed. Symptoms might include tears in your eyes; a burning sensation of skin, nose, or throat; a cough; dizziness or a headache. Toxic materials can take the form of solids, liquids, gases, vapors, dusts, fumes, fibers and mists. How a substance gets into the body and what damage it causes depends on the form or the physical properties of the substance. A toxic material may take different forms under varying conditions and each form may present a different type of hazard. For example, lead solder in solid form is not hazardous because it is not likely to enter the body. Soldering, however, turns the lead into a liquid, which may spill or come into contact with skin. When the spilled liquid becomes solid again, it may be in the form of small particles (dust) that may be inhaled or ingested and absorbed. If lead is heated to a very high temperature such as when it is welded, a fume may be created; a fume consists of very small particles which are extremely hazardous as they are easily inhaled and absorbed. It is thus important to know what form or forms a given substance takes in the workplace. A description of each of the forms follows. Solid: A solid is a material that retains its form, like stone. Most solids are generally not hazardous since they are not likely to be absorbed into the body, unless present as small particles such as dust.Liquid: A liquid is a material that flows freely, like water. Many hazardous substances are in liquid form at normal temperatures.Some liquids can damage the skin. Some pass through the skin and enter the body and may or may not cause skin damage. Liquids may also evaporate (give off vapors), forming gases which can be inhaled. Gas: A gas consists of individual chemical molecules dispersed in air, like oxygen, at normal temperature and pressure. Some gases are flammable, explosive, and/or toxic. The presence of a gas may be difficult to detect if it has no color or odor, and does not cause immediate irritation. Such gases, like carbon monoxide, may still be very hazardous.Vapor: A vapor is the gas form of a substance that is primarily a liquid at normal pressure and temperature. Most organic solvents evaporate and produce vapors. Vapors can be inhaled into the lungs, and in some cases may irritate the eyes, skin or respiratory tract. Some are flammable, explosive and/or toxic. The term vapor pressure or evaporation rate is used to indicate the tendency for different liquids to evaporate.Dust: A dust consists of small solid particles in the air. Dusts may be created when solids are pulverized or ground, or when powder (settled dust) becomes airborne.Dusts may be hazardous because they can be inhaled into the respiratory tract. Larger particles of dust are usually trapped in the nose and windpipe (trachea) where they can be expelled, but smaller particles (respirable dust) can reach and may damage the lungs. Some, like lead dust, may then enter the bloodstream through the lungs. Some organic dusts, such as grain dust, may explode when they reach high concentrations in the air. Fume: A fume consists of very small, fine solid particles in the air that form when solid chemicals (often metals) are heated to very high temperatures, evaporate to vapor, and finally become solid again. The welding or brazing of metal, for example, produces metal fumes.Fumes are hazardous because they are easily inhaled. Many metal fumes can cause an illness called metal fume fever, consisting of fever, chills and aches like the “flu.” Inhalation of other metal fumes, such as lead, can cause poisoning without causing metal fume fever. Fiber: A fiber is a solid particle whose length is at least three times its width. The degree of hazard depends upon the size of the fiber. Smaller fibers such as asbestos, can lodge in the lungs and cause serious harm. Larger fibers are trapped in the respiratory tract; and are expelled without reaching the lung.Mist: A mist consists of liquid particles of various sizes which are produced by agitation or spraying of liquids. Mists can be hazardous when they are inhaled or sprayed on the skin. The spraying of pesticides and the machining of metals using metal working fluids are two situations where mists are commonly produced.Everyone who works with toxic substances should know the names, toxicity and other hazards of the substances they use. Employers are required by law to provide this information, along with training in how to use toxic substances safely. FSM— Source: “An Introduction to Chemical Hazards in the Workplace,” Hazard Evaluation System and Information Service, California Occupational Health Branch, www.dhs.ca.gov/ohb/HESIS/uts.htm.
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