Asphalt is a petroleum product used widely in road paving, roofing, and waterproofing. When heated, it releases a complex mixture of chemical compounds into the air. The resulting aerosol, known as asphalt fumes, consists of vapors and particulate matter. This mixture is produced by the volatilization of lighter components and chemical reactions. Understanding the chemicals involved and their associated health risks is important for those near paving and roofing operations.
The Components of Asphalt Fumes
Asphalt fumes are composed of hundreds of different organic compounds released when asphalt is heated, typically between 150°C and 170°C for hot mix asphalt. The primary concern is the presence of Polycyclic Aromatic Hydrocarbons (PAHs), which are found in the crude oil from which asphalt is derived. PAHs like naphthalene, fluorene, and phenanthrene are common components and are often used as indicators of exposure risk.
The fumes also contain Volatile Organic Compounds (VOCs) and semi-volatile organic compounds (SVOCs). These lighter hydrocarbons contribute significantly to the total airborne concentration and include compounds like linear saturated hydrocarbons and aliphatic ketones. The precise chemical makeup of the fumes varies depending on the source of the crude oil, the type of asphalt used, and the temperature to which the material is heated. A temperature increase of just 20°C can increase the fume concentration by three to seven times.
Acute and Chronic Health Impacts
Exposure to asphalt fumes can lead to immediate and long-term health effects, primarily affecting the respiratory system and skin. Acute exposure often results in irritation of the eyes, nose, and throat. Workers may also experience headaches, dizziness, nausea, and shortness of breath, which typically resolve once they are moved away from the source.
Prolonged or chronic exposure presents more serious health concerns, particularly for occupational workers. Repeated inhalation is associated with long-term respiratory issues, including chronic coughing, wheezing, and reduced lung function. Some studies suggest an association between long-term exposure and conditions like bronchitis.
Regulatory agencies have evaluated the carcinogenic potential of asphalt fumes. The International Agency for Research on Cancer (IARC) has classified occupational exposures to oxidized bitumens and their emissions during roofing as “probably carcinogenic to humans” (Group 2A). The National Institute for Occupational Safety and Health (NIOSH) also considers roofing asphalt fumes a potential occupational carcinogen. This classification is based on the presence of known carcinogens, like certain PAHs, found within the fumes.
Comparing Exposure Levels and Scenarios
The severity of the health risk is directly related to the duration and intensity of the exposure. Occupational exposure, such as that experienced by road pavers and roofers, is considered high-level because it involves daily, prolonged work directly over the hot asphalt source. This close proximity results in inhalation of concentrated fumes, which is the scenario most directly linked to chronic health effects.
In contrast, the general public experiences transient, low-level ambient exposure when near a construction site. Concentrations measured in the general environment are typically very low. For the average passerby, the risk is significantly lower than the risk faced by workers, though sensitive individuals may still experience acute irritation symptoms. A brief exposure to low levels is unlikely to cause the same systemic effects as repeated, high-concentration occupational exposure.
Reducing Exposure and Ensuring Safety
Reducing exposure relies on a combination of engineering controls, administrative procedures, and personal protection. For occupational settings, engineering controls are the most effective measure, including localized exhaust ventilation systems and emission capture devices that pull fumes away from the worker’s breathing zone. Using asphalt mixes formulated for lower emissions or working at the lowest temperature that still meets performance specifications can also significantly reduce fume generation.
Administrative controls involve limiting the time workers spend near high-fume areas by rotating tasks or scheduling work during cooler times to minimize vaporization. Personal Protective Equipment (PPE) provides a final line of defense, including fit-tested respirators with organic vapor cartridges for high-exposure tasks. Additionally, protective clothing and specialized gloves prevent direct skin contact, which can lead to irritation and dermal absorption of harmful components.
For the general public, the most practical measure is to maintain distance from active paving or roofing sites. If an operation is occurring nearby, closing windows and limiting time spent outdoors can help reduce transient exposure. This simple avoidance strategy minimizes the ambient exposure risk.