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AsphaltAsphalt is a dark brown or black substance derived from crude oil. It may be a solid, a semi-solid, or a liquid and is a strong adhesive. Asphalt is often mistakenly confused with "tar", "coal tar", or "pitch" because the appearance is similar and the substances may be used interchangeably in many industrial processes. Tar and pitch are derived from coal products which are chemically and physically different. Other names for asphalt include road tar, road binder, mineral pitch, petroleum pitch, petroleum asphalt, and seal-coating material. Asphalt is used for road paving, roofing tar, roll-roofing, roofing felt, shingles, pipe covering, floor tile, waterproofing, and many other products and processes. Its use will determine what other substances are blended with it and what health and safety hazards are associated with it. There are two main types of asphalt:
HazardsThere are two main hazards associated with asphalt:
Fire and Explosion HazardsMost of the fire and explosion hazard associated with asphalt comes from the vapors of the solvent mixed into the asphalt, not the asphalt itself. The hazard is determined by the flammable or explosive nature of the solvent used and how fast it evaporates. The flashpoint (FP) of a chemical or mixture is the combined measure of this flammable or explosive potential. The flashpoint is the lowest temperature at which enough of the chemical evaporates to form a mixture with air which can be ignited by a spark. The lower the flash point, the higher the fire and explosion hazard. If the flash point is below the room temperature, the chemical is a potential bomb. The flash point — and therefore, the fire or explosion hazard — can partially be determined by the type of asphalt used. There are three types of cut asphalt. The type and amount of solvent (or oil) added determines the properties of the final mix.
The FP of the asphalt and solvent mix will be higher than the FP of the solvent alone. Remember, the lower the FP, the greater the explosion hazard. Table 1 illustrates the various grades of RC, MC, and SC asphalt mixes and their relative flash points.
HEALTH HAZARDS OF ASPHALT
Asphalt fumes are created when asphalt is heated. Fumes contain very small, solid, airborne particles which are easily inhaled by the worker. Inhalation of asphalt fumes can cause irritation to the nose, throat, and lungs. Fumes may also contain hydrogen sulfide vapors, which are very toxic, as well as the vapors generated by the solvents used to "cut" the asphalt. (See below). Exposure to sunlight or other ultraviolet light (such as welding) may make these skin conditions worse.
ASPHALT EXPOSURE LIMITS
HEALTH HAZARDS OF SOLVENT VAPORSVapors from solvents that are used to "cut" asphalt can also present serious health hazards. The solvent vapors generated by heating asphalt are often more toxic than the asphalt fumes themselves. Solvents will evaporate out of the mix at a wide range of temperatures. Heating of the asphalt mix speeds up the evaporation process. The faster the solvent evaporates, the easier it is to inhale. In order to understand the hazards of asphalt, it is necessary to know what solvent is used in the mixture, how fast the substance evaporates, and how toxic the substance is. The boiling point of a chemical determines how fast the substance evaporates. The lower the boiling point, the easier it evaporates and the easier it is to inhale. The toxicity of a substance refers to the effects of that substance on the human body. As indicated above, various organizations — OSHA, NIOSH and ACGIH — recommend exposure limits for chemicals. OSHA's standards are called PELs (Permissible Exposure Limits). OSHA's PELs are enforceable by law in states where public employees arc covered by OSHA or by 0SHA-approved state plans. (Some state plans may have PELs which are more stringent than federal OSHA's PELs.) ACGIH calls its limits TLVs (Threshold Limit Values.) TLVs are only recommended, not required. In theory, a highly toxic chemical will have a very low PEL. In rcality, however, many PELS are outdated and do not take into account new studies about health effects. Others are only based on a chemical's irritant properties, instead of its ability to cause cancer or other serious health effects. It is important to remember that a variety of sources must be checked to determine the toxicity of a chemical and discover the safest exposure limit. Remember, legal does not mean safe. The names of the asphalt-cutting solvents, their boiling points, and any exposure limits should be listed on the Material Safety Data Sheet. Listed below are three solvents commonly used in asphalts, their boiling points, health effects and exposure limits.
Again, in order to understand the health effects of asphalt, it is important to find what solvent was used to "cut" the asphalt mix. Remember that an "RC" mix contains the most dangerous solvents; an "MC" is less dangerous, and an "SC" is the least dangerous of the asphalt mixes. All required and recommended exposure limits (OSHA, NIOSH and ACGIH) should be checked. Remember, the legal limit (OSHA PEL) is not necessarily the safe limit. SAFE WORK PROCEDURES1. Training. All workers exposed to asphalt fumes should be trained about hazards and safe work procedures. This training should include specific information about the solvents used in mixing the asphalt. 2. Material Safety Data Sheets (MSDSs) should be made available to each employee assigned to work with or near asphalt processes. The MSDS should include specific information on the solvents present in the asphalt mix and should list all pertinent information including flashpoint, boiling point, acute and chronic effects of all chemical ingredients in the solution, protective equipment, as well as other fire and emergency cleanup information. 3. Engineering Controls
If the toxicity of the chemical is a problem, the employer may be able to order an asphalt mixture which contains a less toxic solvent (eg. toluene for benzene). Finally, if a less toxic solvent cannot be substituted in the mix, a less volatile solvent may be. Less volatile means that the boiling point of the new solvent will be higher, so less will get into the air to be inhaled.
4. Respiratory Protection. While engineering controls are the preferred method for controlling worker exposure to fumes and vapors, respirators should be worn where this is not possible. In selecting the proper respirator, it is important to know all of the hazards to which workers may be exposed. A NIOSH-approved dust respirator will control exposure to asphalt fumes, but will do nothing to protect the worker against exposure to the toxic vapors given off by the solvent in the mix. In situations where vapors are concerned, the minimum requirement would be for a full-face mask respirator with organic vapor and particulate cartridges. Because of the possibility of eye irritation a half-face mask respirator would be inadequate. Improper use of respirators is dangerous. The employer must have a written respirator program that takes into account workplace conditions, requirements for worker training, respirator fit testing, and medical exams, as described in OSHA standard 29 CFR 1910.134 (see the AFSCME Respirators Fact Sheet). 5. Protective Clothing. Protective clothing is necessary to protect workers from asphalt burns and irritation. In addition, many of the solvents used to cut asphalt are readily absorbed through unprotected skin into the bloodstream, where they can travel throughout the body and cause damage to many different organs. NIOSH recommends thermally-insulated gloves when working with hot asphalt, long sleeve shirts, long cuffless trousers, and metal-toed safety shoes. Clothing should be loose-fitting, collars should be closed, and sleeves rolled down. Safety shoes should be at least 15 centimeters (cm) high and should be laced so that no openings are left through which hot asphalt may reach the skin. 6. Face and Eye Protection. Face and eye protection are also recommended whenever hot asphalt is used. A face shield (8" minimum) should be worn when handling heated asphalt if a full face respirator is not worn. When liquid asphalt is hand sprayed on road surfaces as "tack coat" or "prime coat," spraying equipment with flexible hoses and a long handle should be used. 7. Barrier Creams and Lotions. When applied to the skin, barrier creams and lotions leave a thin film, which acts as a barrier against skin irritants. They should not be substituted for protective clothing but may be useful along with other protective measures. 8. Fire and Explosion Hazards
Revised February 1989 For more information about protecting workers from workplace hazards, contact the AFSCME Health and Safety Program at (202) 429-1228, or 1625 L Street, N.W., Washington, DC 20036.
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