Trichloroethylene as Extraction Solvent for Bitumen in Asphalt Analysis
In 2015 and 2016, the state of Hesse, Germany, measured the exposure to Trichloroethylene among workers in asphalt laboratories and evaluated the RMMs (risk management measures) of 14 Hessian companies. It became apparent that the majority of companies did not fully exploit the possible technical and organizational measures and thus, they did not satisfy all requirements of the German Hazardous Substances Ordinance (GefStoffV). In 2017, further measurements were performed in eight additional selected companies in order to show how good handling of RMMs can reduce Trichloroethylene exposures to a minimum of 1.3 mg/m³ (8h-TWA, 95th percentile).
What is Trichloroethylene?
Trichloroethylene (TCE, TRI) is a colorless, non-flammable but carcinogenic halocarbon widely used as an effective industrial solvent for organic materials such as oil, grease and bitumen. As a dry cleaning agent, the less hazardous Tetrachloroethylene replaced its structural analog as early as the 1950s.
In Germany, Trichloroethylene is still officially required in asphalt testing. Bitumen extractions are performed in so-called asphalt analyzers. Even though these machines are closed loop systems, there are many steps during the whole procedure from loading the asphalt sample into the washing chamber of the asphalt analyzer up to the recovery of the bitumen by rotary evaporation in which workers can be exposed to Trichloroethylene, particularly via inhalation.
Due to its carcinogenic, mutagenic, nephrotoxic and neurotoxic nature, Trichloroethylene is a substance of very high concern listed in REACH’s Authorization List (Annex XIV). The current authorization (REACH/18/9/4) grants its use by downstream users in specific circumstances as an extraction solvent in asphalt analysis only as described in the application by the supplier. This authorization will expire on 21st April 2023. Until then, employers have to protect their workers in asphalt laboratories from Trichloroethylene fumes with measures beyond the RMMs described by the applicant.
Our publication ‘Arbeitsplatzbelastungen durch Trichlorethen in der Asphaltanalytik bei Umsetzung des Stands der Technik‘ summarizes the necessary RMMs as shown below to efficiently protect workers in asphalt laboratories from the hazards of Trichloroethylene.
- Operation of the asphalt laboratory according to the requirements of the TRGS (Technical Rule for Hazardous Substances) 526 “Laboratories“.
- Performance of all operations and processes for Trichloroethylene within fume cabinets, which comply with the requirements of DIN EN 14175-2, or within comparable technical installations, which have been tested for their effectiveness. In addition to the asphalt analyzer and the rotary evaporator, this also includes the bitumen washing machine and the dry box.
- Containers with fresh as well as used Trichloroethylene must be stored in accordance to the specifications of TRGS 510 “Storage of hazardous substances in non-stationary containers“.
- Performance of ancillary work with Trichloroethylene can lead to additional exposure and thus can increase background pollution and is therefore not permitted according to these rules.
- If several installations are operated within one fume cabinet, then this fume cabinet must be fitted with sufficient slides, so that only one part of the front needs to be opened to access the relevant device.
- Installation, connection and operation of the asphalt analyzer and other equipment are to be carried out according to the specifications in the operating instructions of the system’s manufacturer.
- Technical experts must carry out annual inspection and maintenance of the asphalt analyzer.
- The fume cabinet system must be checked at least once per year for function and efficiency.
- To fill the asphalt analyzer with fresh Trichloroethylene or to extract used Trichloroethylene and bitumen Trichloroethylene mixes, the storage or waste containers must be connected directly to the asphalt analyzer via a coupler, so that filling and extracting can be carried out in a closed circuit.
- When extracting the bitumen Trichloroethylene mix, the collecting vessel (usually a round-bottom flask made of glass) must be connected directly with the discharge valve of the asphalt analyzer via a tight coupler. The vapor phase of Trichloroethylene is carried via a pipe either into the tank of the asphalt analyzer or into the waste container where the unused bitumen Trichloroethylene mix is collected (gas displacement procedure).
- The round-bottom flask containing the bitumen Trichloroethylene mix must be kept closed with a glass stopper also within the fume cabinet.
- Trichloroethylene, distilled out when recovering the bitumen, is fed back to the asphalt analyzer via the centrifuge.
- Bitumen polluted work equipment must not be cleaned manually with Trichloroethylene. A closed bitumen washing machine, operated in a fume cabinet, must be used when Trichloroethylene is applied. Suitable cleaning agents, based on vegetable oil esters for example, are available for manual cleaning, which nevertheless has to be carried out within the fume cabinet.
- Also, if the mineral substances (aggregate and filler) are dried in the asphalt analyzer in several runs after the main extraction, it cannot be ruled out that they still contain residues of Trichloroethylene. In order to avoid exposure to Trichloroethylene, mineral substances extracted in the asphalt analyzer must remain within the fume cabinet until they are cooled. Additional drying can also be undertaken in a heated dry box, which must be operated in the same fume cabinet as the extraction system.
- Working surfaces inside the fume cabinet must not be cleaned with Trichloroethylene either. Appropriate cleaning agents, based on vegetable oil esters for example, are available for such purposes.
- The asphalt density is determined by using water only.
- Suitable chemical protective gloves made of fluorocarbon rubber (FKM) must be worn for all work that may result in dermal exposure to Trichloroethylene.
- For risk-free disposal of leaked Trichloroethylene, suitable chemical binding agents, work equipment to take up the chemical binding agents and sealable waste containers as well as appropriate personal protective equipment are to be used (such as the above-named chemical protective gloves, respiratory protection in the form of half masks with a class A filter (for high-boiling organic compounds) or fan-assisted air hood respirators)