A Complete Guide to Benzene
Why is Benzene so hazardous?
VOCs have a significant vapour pressure at normal ambient temperature which means they evaporate (volatilise) at low temperatures so they can easily enter the body through normal breathing but can also be absorbed through the skin or by swallowing material containing it.
The effects on worker’s health depends upon how much benzene they are exposed to and for how long and as with other organic solvents, the immediate effects of a single exposure to a high concentration (hundreds of ppm) e.g. from a fugitive process leak, include headache, tiredness, nausea, dizziness and even unconsciousness if the exposure is very high (thousands of ppm) meaning an acute safety incident.
According to the European Agency for Health and Safety at Work (EU-OSHA) 5, 15 % of workers across the European Union (EU) have to handle dangerous substances as part of their job, and another 15 % report breathing in smoke, fumes, powder or dust at work which could be hazardous to their health. The EU has brought forward essential legislation relating to so-called physical and chemical agents in the workplace over the last two decades and the Chemical Agents Directive 6 is ‘celebrating’ its 20th anniversary during 2018. In the UK, it is implemented as the Control of Substances Hazardous to Health (COSHH) Regulations 2002 and transposition across the EU has been summarised by in an informative document EU-OSHA 7.
In addition, Directive 2004/37/EC 8 was specifically introduced for carcinogens or mutagens at work and essentially requires that the employer assess and manage the risk of exposure to carcinogens or mutagens and to:-
- Limit the quantities of a carcinogen or mutagen at the place of work;
- Keep as low as possible the number of workers exposed;
- Design the work processes so as to minimise the substance release;
- Evacuate carcinogens or mutagens at source, but respect the environment;
- Use appropriate measurement procedures (especially for early detection of abnormal exposures from unforeseeable event or accident);
- Apply suitable working procedures and methods;
- Use individual protection measures if collective protection measures are not enough;
- Provide for hygiene measures (regular cleaning);
- Inform workers;
- Demarcate risk areas and use adequate warning and safety signs (including ”no smoking”);
- Draw up emergency plans;
- Use sealed and clearly visibly labelled containers for storage, handling, transportation and waste disposal.
What are my workplace exposures?
Knowing the obligations of legislation and OELs, the question remains, how do I know if workplace benzene exposures are below the limits for my country? Unlike other health and safety issues that are managed by risk assessment, this can only be determined by monitoring. There are several monitoring solutions on the market including chemical specific detector tubes, air sampling pumps with charcoal tubes or sample bags (later analysed in the laboratory using a GC) but photoionization detection (PID) has proven to be the ideal tool. PID based solution are used in the following ways:-
- fixed instrumentation
- portable instrumentation
- personal instrumentation
Indeed, a combination of all three solutions provides complete worker and environmental protection and these are discussed later in more detail.
PID theory of operation
Figure 3 is a schematic of a proprietary PID sensor system. A UV lamp generates high-energy photons, which pass through the lamp window and into the sensor chamber. Ambient air is pumped over the sensor and about 1% of it diffuses through a porous membrane into the other side of the sensor chamber. The inset on the lower right of figure 3 shows what happens on a molecular level. When a photon with enough energy strikes a molecule M, an electron (e-) is ejected. M+ ion travels to the cathode and the electron travels to the anode, resulting in a current proportional to the VOC concentration. The electrical current is amplified and displayed as a part per million (ppm) or part per billion (ppb) concentration. Not all molecules can be ionized. Conveniently, the major components of clean air i.e. nitrogen, oxygen, carbon dioxide, argon, etc., do not cause a response, but most accelerants do give a ‘broadband’ response.