Benzene – production, use and occurrence
Benzene is a colourless liquid which vapourises at low temperatures. The vapour is colourless, and has a characteristic sweet smell, leading to the naming of its chemical group as ‘aromatic hydrocarbons’.
Benzene is produced as part of the petroleum refining and distillation process, and is used as a pre-cursor component of plastics manufacture. It is transported globally in its liquid form in large volumes.
Benzene is also present in high concentrations as a naturally occurring component of both crude and bunker oil. Individuals may also be exposed to benzene in the following industries:- coal mining and coke production, offshore drilling, petroleum storage and distribution, steel production, shoe manufacture, tank cleaning and hazardous waste disposal, remediation and clean-up, tyre manufacture and fire fighting and emergency services.
Benzene risk and workplace exposure limits
Benzene and other VOC’s ( volatile organic compounds ) have long been recognised as human carcinogens and mutagens ( agents which cause damage to DNA ). Benzene is classed as a ‘Class 1’ carcinogen, and has been demonstrated to cause cellular damage resulting in a number of types of leukaemia.
From a permissible workplace exposure limit of 200 ppm ( parts per million ), in 1920, levels have reduced in stages following increasing research and awareness of the harmful effects of benzene. In 1946 the recommendation the ACGIH ( American College of Industrial Hygienists ) was set at 100 ppm. This level was reduced to 50 ppm in 1947 and 35 ppm in 1948. The ACGIH has adopted Threshold Limit Values (TLVs) for benzene at 0.5 ppm TWA and 2.5 ppm STEL ( Short term exposure limit ).
Leukaemia resulting from benzene exposure has been, and continues to be, the subject of much litigation in the United States, with many appellants receiving substantial damages payments for workplace acquired illness.
The current benzene WEL ( Workplace Exposure Limit ) in the UK and the EU is 1ppm 8hr TWA ( time weighted average) .
The recent implementation of REACH ( Registration, Authorisation and Restriction of Chemicals ) by the EC will now highlight benzene as a SHVC ( substance of very high concern) as it is a known carcinogen and mutagen.
Benzene risk and workplace exposure limits
Until recently, standard methods for determining likely benzene exposure relied on measuring benzene vapour in the atmosphere. This is performed either by use of static monitoring devices in the vicinity of the workplace, or by analysis of a vapour collection tube, worn by the subject whilst working in potential risk zones.
Additionally, routine medical tests have used blood sampling for investigation into abnormalities of the white blood cells, potentially indicative of the early stages of leukaemia.
More recently, tests have been developed to look for the presence of benzene markers, or metabolites, in a donor urine sample. This technique is known as ‘bio-monitoring’ and initially involved analysis of phenol, a major benzene metabolite. Although used for a number of years this method has now been replaced, as it cannot detect to today’s lower exposure limits set by international regulation.
Another metabolite, SPMA, has been identified as a more specific and sensitive marker of benzene exposure. Until recently, however, analysis of SPMA involved lengthy and expensive laboratory testing using GC/MS (Gas chromatography/ mass spectrometry)
In the most recent development Oil Industry scientists worked to produce a new assay for SPMA that was both rapid and highly accurate. The resultant unique immunoassay is used in Argentic’s ‘benzene box’ system, delivering accurate results reporting within 2 days, and proving highly cost effective in comparison with older laboratory methods
The new ‘benzene box’ system from Argentic represents a major improvement in benzene exposure testing. Use of the benzene box and SPMA bio-monitoring now allows clients to easily carry out self tests on at-risk personnel during operations at sea or on land. Employers are now offering workers real-time tests for exposure to benzene. This testing helps to ensure and demonstrate that that appropriate PPE is being used and that it is fitted and functioning correctly. Such testing will be of additional value to the required fit-tests for PPE.
Testing may also be carried out to check and demonstrate that accidental vapour emission is not occurring in living and mess quarters or other designated safe areas.
An additional benefit of SPMA bio-monitoring results from its ability to measure benzene exposure resulting from by ingestion or skin absorption. These exposure routes are not covered by ambient vapour monitoring methods, which only indicate the potential for exposure by inhalation. Argentic SPMA bio-monitoring therefore is able to demonstrate absolutely that exposure has not occurred by any means.
Sampling and testing in practice
Each person has an individual background level of SPMA, and this should be recorded initially, outside of their work environment. Sampling involves the collection of a small volume of urine which is placed in a preservative-treated vial. The vials are despatched to the laboratory using robust packs that are compliant with transport regulations.
Once an individual’s background level is recorded, samples may then be taken before and after carrying out hazardous activities, with the second sample being taken within 9 hours of task completion, e.g. before and after tank cleaning operations.
On analysis, a urine creatinine level is also recorded, to indicate sample dilution as a result of hydration level. Results are then presented as an SPMA to creatinine ratio. Levels that indicate that permitted TWA levels have been exceeded, or approached, are highlighted and toxicological interpretation is provided.
Should a sample show a level of SPMA that indicates exposure to high benzene levels then investigation and remedial actions should be carried out by the client to remove or reduce the potential for exposure, and to ensure correct usage and functioning of PPE.
Testing of employees should also performed on a random basis to demonstrate that exposure is not occurring due to accidental vapour release. This testing should cover working, living or recreational areas where benzene vapours are not expected to be present.
Argentic’s ‘benzene box’ system enables employers to implement a simple, rapid and accurate means of risk minimisation. More frequent and extensive testing of personnel is now feasible, bringing direct benefits to employees in the form of reduced workplace health risk. In addition, employers may benefit from the decreased likelihood of workplace – acquired illness claims.
The use of regular bio-monitoring of personnel for benzene exposure enables: