Asphalt is used extensively in roofing, waterproofing, and, above all, of course, in roadway construction. It comes in many varieties. Typically, it contains less than 10% bitumen, a petroleum distillate, mixed with aggregates and solvents.
The aggregates used may be natural (limestone, granite), artificial (slag aggregates) or recycled (demolition waste, glass, and road planings). Asphalt may also be synthetic, or modified by the use of polymers, and may contain a wide variety of other components, including binders, hardening agents, bonding agents, crushed rock, and sand. As it is a petroleum-based product, asphalt should not be confused with coal tar or pitch, a wholly different product, having its own qualities and hazards. Additives used in recent years in paving asphalt, such as resins and recycled rubber, may present additional, less well-known hazards.
The two primary safety issues associated with asphalt products are the danger of burns, and dangers from respiratory or skin exposure to the product and its fumes.
Of these, the danger of burns from working with hot asphalt is the more obvious one, as paving asphalt is heated to temperatures of between 250 and 325 degrees Fahrenheit, and roofing asphalt may be used at temperatures in excess of 450 degrees. Many asphalt “recipes” are highly flammable, and some are potentially explosive.
In addition, when heated, asphalt’s fumes not only smell bad, but dangerous in in greater or lesser degree (according to what is in the mix). The solvents (e.g., naphtha, toluene, and xylene), binders, and other chemicals used in different asphalt products may be extremely hazardous. Asphalt, especially when stored in unventilated containers, may give off hydrogen sulfide gas which, if inhaled, can cause dizziness, convulsions, coma or death. Asbestos and silica in the rock and sand found in asphalt are associated with lung disease. Styrene can cause nervous system damage. Bronchitis, skin rashes, and eye irritation are further hazards.
Where hardened asphalt is to be cut, drilled, milled or planed, avoiding the inhalation of respirable dust becomes a concern. Aggregates in many asphalt mixes include crystalline silica (quartz) which, if inhaled over a period of time, can cause lung damage, silicosis, and other serious ailments.
Curiously, although a 5 mg/m3 limit was proposed as long ago as 1992 (and, as an average over an 8-hour shift, has the force of law under Cal OSHA, California’s state-administered program) until now federal OSHA has not seen fit to adopt a Permissible Exposure Level for asphalt fumes. The American Conference of Governmental Industrial Hygienists recommends a threshold limit value of 0.5 mg/m3 (as an 8-hour, time-weighted average) and NIOSH recommends the same level as a maximum per 15-minute, short-term exposure. One risk assessment study estimated a significant risk of lung cancer, at levels as low as 0.2 mg/m3..
So, while (apart, perhaps, from the requirement to use PPE while working with asphalt) OSHA does not have construction standards that regulate working with asphalt per se, there are things you can do, as a health-and-safety-conscious highway or roofing contractor, to reduce asphalt-related hazards to your employees.
A first thing you can do is to get expert advice regarding which asphalt mixes, available in your area, are the least toxic, while suitable to the work you perform. Of course, your contracts may prescribe that particular mixes be used, but you may be able to negotiate a substitution, if you can identify an equivalent product that is less toxic and therefore safer.
Since asphalt products differ from one another in their composition and their uses, it’s a good idea, also, to study and to circulate the manufacturers’ Material Safety Data Sheets for the products that you use.
A critical element of the safe use of paving asphalt, with both highway-class and non-highway-class pavers, is the proper cleaning, maintenance and periodic testing of the equipment. NIOSH, as well as the equipment manufacturers, publishes detailed guidelines on how the equipment can be maintained, to minimize worker exposures.
As always, training your employees, and emphasizing safe practices, and the enforcement of safety rules and procedures, are critical.
Rule #1 for employees is probably to avoid breathing asphalt fumes whenever possible. Workers should never stick their heads into an asphalt tank or mixing container, or lean over a kettle. While asphalt fumes are generally not believed to be acutely hazardous while asphalt is being laid in open-air situations, the continuous inhalation of high-vapor concentrations — as may arise in poorly-ventilated, confined, or semi-confined spaces — is to be avoided. Additional ventilation, and/or the use of respirators, may be required.
PPE (Personal Protective Equipment) should be used when working with asphalt. Overalls and/or long-sleeved jackets and full-length trousers (without cuffs) should be worn to protect skin from burns. Heat-resistant, impermeable gloves, and safety boots should be worn to protect hands and feet. If there is any danger of product (including dust) getting in employees’ eyes, goggles should be worn.
Workers should never eat, drink, or smoke while working with asphalt, and, indeed, hands should be washed thoroughly, before handling or eating food or drink. Asphalt should be kept away from ignition sources. Asphalt can cause lung damage, or even death, if swallowed.
Workers should be instructed, and regularly reminded during toolbox talks or at other opportunities, that they should stop working, and consult a foreman, if they experience dizziness, or other symptoms associated with exposure to asphalt or its fumes.
In case of inhalation, the employee should be removed to fresh air immediately. If the employee has trouble in breathing, seek medical attention at once. If the employee has stopped breathing, administer resuscitation, and seek emergency medical assistance.
Burns should be flushed immediately with large amounts of cold water. Except if necessary to allow breathing, do not attempt to remove anything from the burn area. Bitumen should be removed under medical supervision. Seek medical attention at once.
Apart from ingestion of the material (or the inhalation of dust where it is being cut, milled, etc., the primary dangers of asphalt (burns, fumes) have to do with the heating of the product. In case of ingestion, if the person is conscious, he should rinse out his mouth, and be given water to drink.
In case of fire, dry powder or foam (and not water or carbon dioxide) should be used to extinguish the fire. Hydrocarbon fumes, as well as smoke, may be released during a fire involving asphalt products. If first responders are summoned, advise them as promptly as possible that the fire may involve asphalt products, so that appropriate measures may be taken to protect the firefighters and other first responders.
There are many reasons for the perennial popularity of asphalt, especially for road surfaces and parking lots. It’s durable, and can be milled for recycling and resurfaced. It offers speed and cost savings in construction, as well as reductions in noise pollution. Treated with the necessary respect, it’s an extremely useful material. However, precautions must be taken not only against burns, but against the fumes and gases that the product gives off.