Method for the measurement of benzene in the low ppb range in working areas

Status:

completed 10/2013

Aims:

Benzene is classified as a Category 1A human carcinogen and Category 1B germ cell mutagen. The EU has specified a binding occupational exposure limit value (BOELV) of 3.25 mg/m³. An acceptance concentration of 200 µg/m³ for benzene, based upon exposure-risk relationships for carcinogenic substances, applies in Germany. The measurement method used to date for benzene does not satisfy the minimum requirements to EN 482, "Workplace atmospheres – General requirements for the performance of procedures for the measurement of chemical agents" for this substantially lower concentration range. The method also presents only limited scope for modification. A new method was to be developed for the measurement of benzene in working areas which fully satisfies the requirements for a measurement method.

Since it can be anticipated that the limit will be lowered further in only a few years' time, a detection limit of 1 µg/m³ over the entire method was made an objective.

Activities/Methods:

Thermal desorption was to be used as the measurement method. Since the Tenax TA generally used as the sampling material at the IFA is of only limited suitability for benzene, which is relatively volatile, an alternative sampling medium had to be found. Analysis was to be performed by means of gas chromatography with detection by mass spectrometry.

The complete validation process to EN 482 and to EN 1076, "Workplace exposure – Procedures for measuring gases and vapours using pumped samplers – Requirements and test methods", was conducted during development of the method. All parameters were to be determined, such as the expanded uncertainty of measurement, recovery rates for various concentrations, storage life of the coated sampling media, and detection limit.

These data were to be used to produce a standard work instruction and a description of the method for the IFA folder.

Results:

An analytical method for monitoring the exposure-risk relationship for benzene in the room air at the workplace was developed and validated in the course of the project. Thermal desorption tubes filled with Carbopack B 40/60 (200 mg) and Carbopack X 40/60 (270 mg) were used for adsorption. Sampling air was drawn through the tubes for 60 minutes at a rate of 33 ml/min by means of a suitable pump. Mass-selective detectors were used for quantitative analysis. Calibration according to the method of the internal standard (e.g. deuterated toluene) is necessary. The method has a detection limit of 2 µg/m³. The method was validated by the performance of comparative (static) measurements at a number of workplaces, including at filling stations, fuel depots and automotive workshops, and on garden tools. A standard work procedure was produced. The description of the method was published in the IFA folder. The method satisfies all requirements for measurement methods for hazardous substances in working areas, and has been included as a standard method in the MGU measurement system for exposure assessment.

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