In-Field Measurements of Benzene Vapour: Contaminated Land and Industrial Hygiene
What is Benzene and why is it of Concern to me?
Benzene (C6H6), is an organic compound that is highly volatile, flammable and carcinogenic (causes cancer). It is often found in:
Petroleum refining (Oil refineries)
Coke and Coal manufacturing
Rubber tire manufacturing
Storage sites (tank farms)
Transportation services (ships, tanker trucks)
Laboratories
and, Chemical manufacturing
Hence, benzene is encountered on a regular basis in the remediation field on sites contaminated with petroleum spirit, former coke works or disused chemical manufacturing premises.
Exposure to benzene is crucial to all concerned, with it posing an Immediate Danger to Life and Health (IDLH) at concentrations of ca. 500ppm; likely causing death, or immediate/delayed permanent adverse health effects. As such, it is very important that exposure be for limited periods during routine and non-routine operations, with adequate protection in place for skin, eyes and respiratory tract. The long term effects of benzene exposure to lower concentrations can be:
Bone marrow suppression leading to serious blood disorders such as anaemia;
Cancer – forms of leukaemia and other white-blood-cell cancers.
It is also suspected of being a toxicant to numerous critical to life systems, such as, cardiovascular, endocrine, gastrointestinal, immunological, neurological and respiratory systems.
So, it is of paramount importance that we take the management of benzene exposure to people and the environment seriously. Within the workplace, exposure limits are set at 1ppm average over an 8 hour period (TWA) in the UK, and more stringent in the U.S. with 0.5ppm as a TWA and 2.5ppm maximum over a 15 minute period (STEL).
How do I measure benzene?
There are many technologies that are available to detect Benzene; however, each has its strengths and limitations. Our primary consideration is to meet regulatory requirements to monitor and protect the health and safety, but also to identify potential contamination in soils and sediments on construction and remediation sites. Many gas detection monitors are available and include:
Multi-gas monitors
Gas detection tubes
Laboratory Gas Chromatograph techniques (GC-MS/FID)
Portable GC products
Photoionization detectors with filter tubes
However, for infield measurement techniques we are largely limited by cost, ease of use and sensitivity. As such, gas chromatography is eliminated on grounds of cost and ease of use, multigas monitors with O2, the lower explosive limit (LEL) of combustible gases, carbon monoxide (CO), hydrogen sulfide (H2S) and PID, are not suitable as they lack specificity or the resolution required for the measurement of benzene.
This limits us to using gas detection tubes or photo ionisation detectors with filter tubes.
Single-use Gas Detection Tubes
Colourimetric gas detection tubes have been used for gas detection for many years. These function by exposing a gas sample to a reagent.
If the chemical of interest is present then a chemical reaction will occur and a colour change in the tube is observed. The concentration of Benzene is determined based on the length of colour change observed in the tube. Tubes are an inexpensive and have a legacy or history of being used to monitor toxic gases in the ppm range. This type of monitoring technique has several limitations:
Tubes only provide one-time snapshots.
They do not provide continuous monitoring with alarms.
The “spot check” nature of tubes also makes them more prone to sample error.
Tubes are slow to respond.
They give readings in minutes rather than seconds.
Tube readings are subject to interpretation.
Tubes expire
The accuracy of detector tubes is usually agreed to as +25%
PIDs with Pre-filter Tubes
While PIDs are broadband detectors, they can give benzene-specific response by using a combination of a low-energy (9.8 eV) Ultraviolet lamp and pre-filter tubes that remove organic interference's. This system provides rapid response down to 0.05 ppm in one minute with an accuracy of +/-10%. Measurements of TWA-levels of benzene can be made in the presence of up to about 300 ppm of petroleum spirit. The tubes also absorb moisture and thus benzene-specific measurements can even be made in steam vents. Compared to portable gas chromatographs, the PID-Filter systems are much smaller and lighter, considerably less expensive, easier to operate, much faster, and provide about the same accuracy and detection limits. The instantaneous feedback enables workers to make rapid PID personal protective equipment decisions and allows them to perform their job tasks with confidence that they are not being exposed to hazardous levels of benzene.
Therefore, for real time monitoring of benzene PIDs with pre-filter tubes present the best in field option. There are a limited number of options of these on the market, but the best is the UltraRae 3000 from Rae Systems by Honeywell, being the most well-built/sturdy and accurate by far. It is ideal for occupational hygiene monitoring, but also soil and water headspace testing. It shares the same platform as the MiniRae 3000, so is proven as a reliable option for both these applications. A new alternative is also the MultiRae Benzene, which is a multi-gas monitor with PID and benzene specific filter tubes, with much of the functionality of the UltraRae 3000 but with slightly less resolution or the ability to take STEL measurements (but still a good option).
If you would like to know more about this application or require any assistance with monitoring technology please feel free to contact Environmental Science & Technology Ltd, on +44(0)1904 373 018 or info@environst.com.
