Strategies for measuring benzene

In many processes, benzene has been replaced with less toxic substances in recent years. However, in some industries the presence of benzene simply cannot be eliminated, such as oil refineries, petrochemical plants, offshore facilities and coke works. Activities like crude oil distillery, fracking, manufacturing or any tasks near engine emissions and combustion products risk impacts on human health. However, incidents of work-related cancer and other illnesses caused by exposure to benzene can be prevented with strategies for measuring benzene in every possible work scenario.

To protect personnel from risks of exposure to benzene vapours, the UK workplace exposure limit (WEL) values for benzene are extremely low at just 1ppm over an 8-hour period (EH40 LTEL). The EU is also currently reviewing a recommendation by the Committee of Risk Assessment (RAC) to lower the limit to 0.5ppm for member states, and there is a possibility the UK will also move to these lower limits in future. Organisations must ensure they stay within these low legal exposure limits by establishing strategies for precise and reliable monitoring.

Challenges of benzene monitoring at low concentrations

As exposure limits have been reduced so drastically for benzene in recent years even the lowest concentrations must be detected to adequately protect workers and ensure organisations continually stay within official thresholds. This means that monitoring benzene has become increasingly challenging.

The impacts of lower thresholds on industry are:

• More areas on an industrial site have to be monitored for benzene (and other VOCs)
• The number of measurements to be performed/frequency of measurement increases
• Measurement speed and costs per measurement are more important as a consequence

Benzene detection tasks must be carefully planned by safety managers to ensure measurement solutions are quick to perform and as economical as possible, without any compromise to worker safety or health. This creates a balancing act between ensuring quality and saving both time and money.

Benzene measurement objectives, methods and technologies

The objectives for measuring benzene vary but can include

• Clearance measurement prior to confined space entry
• Checking average contamination values
• Searching for suspected leaks
• Precisely locating peak exposure sites

Different companies implement regulations very differently. Some clear all work areas once a year, others examine individual work steps and attempt to precisely locate peak exposure sites. The goal is to make these critical work steps safer through technology and safety processes. If frequent benzene monitoring must be carried out, reusable equipment solutions rather than, for instance, single-use detection tubes offer greater long-term business value. The planned benzene measurement task determines the measurement method to be used. Here, we look at the different measurement methods.

• Laboratory measurement: On-site air sampling using a pump and canister vessel can be analysed by gas chromatography. This separates VOCs that are collected simultaneously to ensure a specific, accurate measurement reading for benzene. An efficient receipt of laboratory results is dependent on forward planning for transporting samples to the laboratory. Results analysed by a lab can reliably determine either very high or low concentrations of benzene.
• Badge monitors: Passive or diffusion collectors known as “badges” consist of a collection medium, such as active charcoal, and a strip at the front that has contact with the surrounding air. If a worker’s exposure to benzene should be monitored, a badge is fixed onto clothing/PPE at the inhalation area. Due to the relatively low concentrations of substances in the air of interior rooms, a series of samples may be needed over several weeks to identify substances in the relevant concentration range. The badge is evaluated in the laboratory, while the collected substances are analysed selectively. Only average values may be recorded, and exposure peaks are included within this average value.
• Detection tubes: Detection tubes can be used to detect benzene precisely, quickly, and economically. The 0.25/a Dräger-Tube® measures to the lowest concentrations above 0.25 ppm. Detection tubes can easily be operated by non-experts using a hand pump – even in Ex areas. They are suitable for air analysis in confined spaces, for detecting leaks or peak concentrations, and for measuring contamination of specific work areas.
• Photo-ionisation detection (PID): PIDs are ideal for locating hydrocarbons, especially in very low concentrations, and provide selective (with gas chromatograph technology) or non-selective measurements. Where a non-selective PID is used (such as in the Dräger X-am 8000), if a critical hydrocarbon level is detected after a measurement reading, a subsequent selective measurement is needed to clarify exactly which substance accounts for the highest proportion of the overall concentration. However, a selective PID device such as the Dräger X-pid 9500 with gas chromatography will already provide the isolated concentration. PID devices cost more but their advantages offer a certain return on investment. For instance, they can monitor continually to then produce a ”concentration profile” using the results of a workplace across an entire shift. This makes it easy to detect peak exposures that occur during particular tasks or processes.
• MicroTubes and analysers: A MicroTube opto-electronic analysis device is ideal for detecting benzene precisely in extremely low concentrations. MicroTubes combine with the Dräger X-act® 7000 to measure benzene in the 1 – 150ppb range. The substance-specific reactive layers and multiple pre-layers in the MicroTubes allow for selective gas testing. During testing, the various layers filter out other substances that occur in the workplace so that only the benzene is reflected in the test result. This greatly eliminates cross-sensitivities and reduces the number of false-positive test results and false alarms. This technology is fast and easy to use, even in Ex-areas.

Combining different methods as intelligent solutions for benzene measurement

In practice, companies usually require a combination of different measurement methods. For example, further monitoring is often required after clearance. Each benzene measurement method usually has a specific focus, ideally suited to either clearance or monitoring tasks, but not equally for both. For this reason, it makes sense to combine methods – especially if benzene needs to be detected in very low concentrations. Innovative technologies allow the combination of these methods by unifying them in one device. The most comfortable, quickest way to measure benzene concentrations under 1 ppm is by using an innovative PID with integrated gas chromatograph such as the Dräger X-pid 9500.

Costs are an important factor in deciding on the measurement method, but other criteria are also seeing increased focus. The measurement itself should be as straightforward as possible to carry out. Safety levels increase significantly if (often human) errors in operation, evaluation and data transfer can all be avoided throughout these processes. Further gains in efficiency result from digital data transmission. This speeds up documentation processes significantly and simplifies analysis. Another decision-making factor for improving both safety and efficiency is if the same measuring solutions can be used for measuring other hazardous substances, besides benzene. Newer, innovative measuring systems thus open up new perspectives for the safe handling of carcinogenic and other hazardous substances to ensure both efficiency and safety in the industry.

For further information and assistance with your benzene measurement strategy, please do not hesitate to get in touch with Dräger.