Asphalt: prevention remains a priority
Solutions to better protect the health of employees
Over three million tons of hot mix asphalt are spread on French roads every year. The use of this bitumen, made from distilled petroleum, can be a health hazard for workers.
Making roads requires the use of mixed asphalt, composed of gravel, sand and bitumen. The latter is produced by vacuum distillation of petroleum. The asphalt tends to release fumes containing dangerous substances (carcinogens, irritants, etc.). The International Agency for Research on Cancer (IARC) classified exposure to bitumen fumes during road surfacing work as a group 2B possible carcinogen for humans.
Since 1986, in cooperation with the regional prevention services of the French Social Security system, INRS has carried out several studies on employee exposure to these fumes and on their toxicity. Since 2011, a working group composed of INRS, professional associations, the Ministry of Labour, the ‘Prevention’ network, and others has reviewed chemical risk prevention schemes used in road surfacing work. Three primary areas for improvement were identified :
- The emission source : the bitumen. Develop methods to measure exposure to bitumen fumes as a tool for assessing means to reduce exposure
- The equipment : Changes to the equipment used to make roads (pavers, milling machines) to limit exposure
- The human factor : Conduct an ergonomic study to find suitable prevention solutions related to work practices and organisation.
The development of methods to measure exposure to bitumen fumes as a tool for assessing means to reduce exposure
When a road is surfaced, asphalted or sealed, workers are exposed to bitumen fumes : a complex mix of organic compounds in gas and particle form. Due to both proven and suspected effects of these fumes on health, measuring exposure during these activities is essential.
In France, an estimated 4,000 people are believed to be exposed. Other sectors use bitumen-based products, in the construction of dams, canals, reservoirs, waste confinement, and in the creation of industrial land. INRS recently developed and validated a global method of measuring exposure to hydrocarbons on road projects.
The approach consists in characterising the fumes from different types of bitumen used in France with the help of a tool which generates and condenses fumes made in a laboratory setting. Then, a measuring method (M-2) was developed which could measure an equivalent exposure index for any type of bitumen.
The method was deployed as part of a national campaign (2014-2015) for a representative assessment of occupational exposure to bitumen fumes in France (involving 41 sites and 304 readings). The representative character of the measurements was guaranteed by selecting road construction sites based on knowledge of the sector and by the implementation of a rigorous sampling strategy.
This campaign also made it possible to assess the effectiveness of prevention methods on operator exposure to fumes and promote the best methods going forward. The goal is to identify what is technically possible in terms of prevention.
Adapting the equipment used to make roads (pavers, milling machines)
Beginning in 2011, in tandem with a study on the reduction of exposure to bitumen fumes during road surfacing, the working group composed of INRS and its partners reviewed the effectiveness of fume extraction systems in pavers, the moving units used to apply asphalt on the road.
Fume extraction was found to be recommended : not only does it reduce operator exposure, it also improves their comfort by protecting them from the heat. These recommendations were followed and the majority of pavers now offer an integrated fume extraction system. INRS measured the effectiveness of fume extraction based on the NIOSH 97-105 protocol of our American counterpart and experimental methods in order to cover the majority of ways the equipment might be used.
System effectiveness, measured using the NIOSH 97-105 protocol, must always exceed 80 % for real effectiveness in the field. The NIOSH 97-105 method is the only standard available today to evaluate the performance of paver extractors, but is designed for American equipment. The protocol needed to be adapted to European equipment. A project with NIOSH was launched in 2013 and procedures for applying the protocol to European models were developed.
To generalise the practice, a review was conducted by the ISO TC 195 standardisation group, charged with developing standards for mobile equipment used in road construction. A working group was set up in 2013 to develop and draft a proposal on paver fume extraction systems with the goal of including an appendix on extraction systems to the draft EN ISO20500 standard.
The national exposure measurement campaign in 2014-2015 confirmed an approximately one-third reduction in operator exposure on sites where the paver was equipped with an extraction system.
The question of extracting dust and silica dust during the recycling of roads was raised. Based on a NIOSH report following an eight-year study (NIOSH 015-105, Control Worker Exposure to Respirable Crystalline Silica during Asphalt Pavement Milling), INRS recommended the use of extractor-equipped road milling machines which passed American tests.
Ergonomic study to identify suitable prevention solutions related to work practices and organisation
An exploratory ergonomic study was launched with the aim of identifying situations or operating modes which involve skin exposure to bitumen and other chemical products. It provides preliminary information for the assessment of skin exposure or surface contamination.
Analysis of the activity is the guiding thread of the approach. It is based on observational data from video recorded on road construction sites. Work hypotheses and a characterisation tool for skin contact were created. In addition to this analysis, a subjective assessment was carried out on the risk of skin contact with bitumen by collectively comparing video observations.
Results suggest that skin exposure to bitumen may be more frequent during phases when workers are waiting than phases of work. It was found that operators do not systematically wear gloves despite the recommendation to do so. This absence of protection appears to be linked to not perceiving the chemical risk of skin contact. Operators are primarily susceptible to burns.