strategies for measuring benzene

© Drägerwerk AG & Co. KGaA 1

The use of benzene cannot be eliminated in the petrochemical and other pro-cess industries. Workplace limit values are strictly low, to protect personnel from risks of exposure to benzene vapours. Organisations must ensure they stay within these thresholds by establishing strategies for precise and reliable monitoring.

Strategies for

measuring benzene


STRATEGIES FOR MEASURING BENZENE

In some lines of business, such as solvent production, benzene has been replaced with less toxic substances in recent decades. As it remains an essential substance for other operations, its use cannot be avoided altogether. Work-related exposure can occur at oil refi-neries, petrochemical plants, coke works and offshore facilities. Ac-tivities 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.In recent decades benzene has been subject to strict Workplace Exposure Limits (WELs) in Europe and similar thresholds world-wide. Workplace detection and monitoring of benzene levels are essential to the adherence to occupational health and safety re-gulations to prevent prolonged or excessive exposure to benzene.

Benzene is a highly volatile, flammable and toxic hazardous subs-tance. Negative health impacts from exposure to benzene via inha-lation have been proven to include dizziness and convulsions in the short term and acute haematological diseases, including blood and lymphatic cancers, in the long term.

Occupational exposure limits for benzeneThe first ever case confirming a link between workplace exposu-re to benzene and leukaemia was in 1928.1 However, managers at this time thought staff rotation for tasks involving benzene – on a monthly basis – was an adequate safety measure. A similar lack of knowledge or caution continued in the following decades. Long-term epidemiological studies have proved occupational exposure to benzene has a direct health impact in workers on chemical plants, many of whom died from leukaemia, multiple myeloma or lymphoma throughout the study periods. Such research prompted the IARC to classify benzene as a Group 1A carcinogen.



Challenges of benzene monitoring at low concentrationsAs legal WELs 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 mana-gers 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.

Coming soon: new lower benzene limit values for the EU The UK WEL is currently 1 part per million (ppm) of air averaged over an 8-hour period. The EU-wide limit was recently the same, with some countries already opting to impose lower nationwide li-mit values. For instance, in Germany, there is already a “tolerable exposure limit” of 0.6 ppm as part of the Risk Acceptance Concept. The Committee for Risk Assessment (RAC) recommended the reduction of benzene limit values to 0.5 ppm for all EU countries, in the past few years, stating, “An occupational exposure limit value of 0.5 ppm (1.6 mg/m3) would reduce the range of best estima-ted lifetime risks down to 0.25-3.3 additional leukaemia cases per 1,000 exposed to 0.5 ppm, corresponding to an exposure of 20 ppm-years.” 2

This new level was officially proposed by the RAC in September 2020 for the EU region, as part of the Beating Cancer Plan and to ensure occupational health equality between member states. The proposal will be discussed by the European Parliament and Coun-cil. It is also possible that the 0.5 ppm value may be approved as an interim level before lowering the limit value even further in the coming years to around 0.2 ppm.3

References:

1 - https://www.eea.europa.eu/

2 - https://ec.europa.eu/commission/presscorner/detail/en/qanda_20_1690

3 - https://ec.europa.eu/social/BlobServlet?docId=23009&langId=en



Laboratory measurementOn-site air sampling using a pump and canister vessel can be ana-lysed by gas chromatography. This separates VOCs that are coll-ected 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 la-boratory. Results analysed by a lab can reliably determine either very high or low concentrations of benzene.

Badge monitorsPassive or diffusion collectors known as “badges” consist of a coll-ection 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 va-lues may be recorded, and exposure peaks are included within this average value.

Photo-ionisation detection (PID)PIDs are ideal for locating hydrocarbons, especially in very low concentrations. However, they cannot measure benzene selectively. Therefore, if a critical hydrocarbon level is detected after a sum-measurement reading of the PID sensor, a subsequent selective measurement is needed to clarify exactly which substance ac-counts for the highest proportion of the overall 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.

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 equip-ment solutions rather than, for instance, single-use detection tubes offer greater long-term business value. The planned benzene mea-surement task determines the measurement method to be used and there is a difference between selective and non-selective me-thods.

Detection tubes, chips and diffusion collectors or laboratory results can produce isolated data. Photo-ionisation detectors (PID), on the other hand, only measure the sum of all volatile hydrocarbons in the air. Therefore, PIDs need to be combined intelligently with selective methods. New technologies offer the possibility to select between different measurement solutions. Depending on the measurement task, its frequency and specific requirements on quality and conve-nience, various measuring methods are possible.



Detection tubesDetection tubes can be used to detect benzene precisely, quickly, and economically. The 0.25/a Dräger-Tube® measures to the lo-west 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.

MicroTubes and analysersMicroTubes are ideal to detect benzene precisely in the low ppb range. The MicroTube Benzene 1 – 150 ppb measures to the lowest concentrations from a concentration of 1 ppb. This makes it the only direct-indicating measuring system that meets the required low acceptance limits. The system Dräger X-act® 7000 and MicroTubes

is immediately ready for use and especially suitable when ease of use is key – even in Ex-areas. It can serve as a pre-test to classic, but expensive, laboratory analyses.

Partners for laboratoriesDespite their high-performance, Dräger’s benzene detection equip-ment has not been developed to compete with laboratories, but rather to partner with them. Laboratories take responsibility for the measurements and subsequent reports that can be used in legal proceeding if needed, for example. Laboratories can use results from independent analysis as a pre-test which is cost-effective, as more complex analyses would only be carried out if a device reveals a critical concentration.



LaboratoryMethod Gas detection tubes with pump

Measurement devicesfor sum measurements and selective measure-ments of VOCs

PID with gaschromatograph

Gas detection with MicroTubes & Analyser

Example device Dräger-Tubes® with Dräger accuro

Dräger X-am® 8000 Dräger X-pid® 9000/9500

Dräger X-act 7000 & MicroTubes

Selective Measurement possible?

Yes In combination with benzene selective tube

Yes YesYes

Measurement range 0.1 ppm or1 to 2,000 ppm

From 0.05 to 2,000 ppm (depending on a sensor type), gas: isobutene

From 0.05 - 25 ppm (limit of detection:0.02 ppm)

From 1 – 150 ppb and 0.15 – 10 ppm

Practically unlimited

On-site application possible?

Yes Yes Yes YesNo

5 minutes 5 minutes (incl. selective tube measurement)

1 minute 25 sec to 15 min depending on the concentration

Several hoursTime factor

Cost range at all Low Low High MidVery high

Procurement cost3 LowPump: Dräger accuro-Set: approx. €300

Average Dräger X-am® 8000 with Ex- O2-, CO-, H2S- and PID sensors: approx. €3,000, incl. charging device

MidX-act 7000 approx. €3,000

MT: approx. €15 per measurement

None (if used as external services)

HighDräger X-pid® 9000/9500: approx. €18,000

Costs per measurement5

Average – depending on use frequencyCost per tube:Time needed:minutes ->Assumption:measurement on average

€5-104-8€3

€9,5 per

LowAssumption: €5 per measurement on averageA tube measurement takes in average 5 minutes => €2.5 labour costs, a measurement without tube 2 minutes.

Average – depending on use frequencyCost per MicroTubes: €15

Time needed: approx. 5 mins-> €2.5Assumption: €15 per measurement (set of 10 measurements costs €150)

Very high, approx. 70 € Very lowAssumption: €0.5 (only labour costs)

Specifics Selective measurementin good quality, no main-tenance or lead time,outside influences(temperature and humidity)affect measurement results.

No selectivity, fast aspre-test, occasionalcombination with pre-tubes possible.

Accurate readings,detection of ppbconcentrations, whichare only possible withlaboratory analysis,easy to use.

Very precisesubstance-specificmeasurement, longwaiting times due totransport routes.

Accurate readings inlow range, selective,immediately available,easy to use, compensatesfor external influences(temperature and humidity).

Further aspects Requires practice, severalminutes needed permeasurement, disposableitems required.

Only pre-test option, no selectivity, occasional combination with selected pre-tubes.

Training needed, mainte-nance and preparationsteps necessary, use issupported by a digital assis-tant, digital data transfer.

Requires practice, severalminutes needed permeasurement, disposableitems required.

Error potential whilesampling, trainingrequired, thus highercosts for serviceproviders.

Digital data transfer possible.

Maintenance andpreparation stepsnecessary, no disposableitems required, digitaldata transfer possible.

Evaluation of measure-ment quality in total

5 6 9 910

Evaluation of measure-ment convenience in total

5 7 10 101

COMPARISON OF DIFFERENT MEASURING METHODS



Combining different methods as intelligent solutions for benzene measurement For clearance of tanks and other confined spaces, PIDs with pre-installed tubes, detection tubes with a pump and also selective eva-luation of benzene in measurement laboratories are all suitable. The combination of a PID with a selective pre-tube is cost-effective. One method is to use a gas detection device with a PID sensor that can utilise a pre-tube for benzene. During a pre-test, the PID measures the sum of all occurring hydrocarbons. Based on this knowledge it will be decided if further ventilation is required. For example, if the sum of hydrocarbons in a benzene tank is already below the defined maximum value during the pre-test, then selective measurement in a second step measures the benzene value using a pre-tube for the PID or single detection tubes. A pre-tube can act as a filter for all hydrocarbons except benzene. Only benzene passes through the pre-tube, allowing the PID to give a benzene-specific reading. The result is available after a few minutes when using this method. The

advantage of this process is fast results which enable safe decisions and improve cost-effectiveness through the use of specific tubes.Using a multigas detector for this application provides the advantage of purchasing, servicing, training and transporting only one detector in the field which serves all purposes, including clearance measure-ments for confined space entry, leak search and benzene readings. Selective measurement with tubes or pre-installed tubes may be omitted if the overall contamination by hydrocarbons is sufficiently low. Low limit values, like those imposed for benzene, may mean substance-specific monitoring might be necessary by repeated measuring. Using a system of an analyser with MicroTubes focuses on measuring carcinogenic and toxic substances in the low ppb range. This sensitive testing system is based on colorimetric chemi-cal sensors which can provide precise on-site results, making them even capable of replacing conventional laboratory analyses.



DRÄGER SOLUTIONS FOR THE COMBINATION STRATEGY

Selective measurement

If the total sum of volatile hydrocarbons is < 10 ppm,

then another selective measu-rement for benzene is taken with tubes, CMS, or PID with a pre-installed tube. Precise

and selective measurement of concentrations of 1-150 ppb can be performed with the

Dräger X-act 7000 with Micro-Tubes. The Dräger Tubes® can measure in the ppm range of 0.25-10 ppm.

Monitoring

Monitoring work with the Dräger X-am® 8000/PID

Substance-specific analysis

Regular laboratory analysis of samples for qualification of hydrocarbons (sum of

VOC to benzene)

Clearance

The pre-test is completed with the Dräger X-am®

8000/PID: Alarm thresholds are set according to the

hydrocarbon qualification, e.g., 10 ppm for a petroleum tank. The pre-test is done in the scan mode with the

Dräger X-pid®

3 Occupational Safety and Health Guideline for Benzene. https://www.cdc.gov/niosh/docs/81-123/pdfs/0049.pdf (2016/10/17)

Combining pre-tests with the analysis by a gas chromatographAnother innovative method is to substitute the measurement by using a PID-sensor with a combined gas chromatograph. This de-vice combines pre-tests with selective tests, therefore simplifying and shortening measurement processes. Two measuring modes, one broadband measurement in scan mode and one selective mea

surement in analysis mode, eliminates the need to carry out manual tube tests and increases safety through laboratory-quality measure-ment results. Initial procurement costs are higher, but frequent use, broken down per measurement, offers a favourable ROI.



Reliable workplace monitoring In the petrochemical industry, contamination levels often show sig-nificant fluctuation. While exposure can briefly be very high during refilling, sampling, and other work at open hatches, it is practically zero in office areas and outside. The amount of benzene employees are exposed to during a shift depends on their particular activities and the concentrations involved. After successful clearance measurement of an area suspected of containing hazardous compounds, the work area still must be conti-nually monitored. This can be achieved using gas detection devices with a non-selective PID-sensor positioned in the work area. They quickly react to changes in concentration and immediately indicate if limits are exceeded. The alarm threshold is adjusted according to the limit value. When an alarm is activated, work must stop im-mediately. PID devices offer the additional advantage of data being recorded and archived for later analysis. Because of the non-selectivity of the PID-sensor, regular selective

spot measurements should also be carried out for workplace mo-nitoring. The Dräger X-act 7000, for instance, allows for immediate precise measurements with the pre-calibrated MicroTubes. The fre-quency of the spot measurement depends on precise risks in ac-cordance with risk evaluations, which also determines the preferred measurement methods. In principle, these repeated measurements correspond to the clearance measurement method. To calculate the average benzene concentration in the workplace, a sample should be taken across the entire work shift (usually 8 hours), or a series of sequential samples taken by spot measure-ments should be carried out every 30 minutes. Ideally, the sample should be taken from a location where the com-position of the atmosphere represents as accurately as possible the air that the employee would be inhaling. For instance, of three samp-les each taken for a 15-minute duration, the sample with the highest value is given as the maximum concentration.

CHANGING CONTAMINATION

0.03

2

4

6

8

10

8 am shift starts 5 pm shift ends

Exposure hydrocarbons (ppm)

Exposure benzene specific (ppm) – not detectable continuously

Average exposure benzene (ppm): Shift average detected with badge

Filling a tank gasoline exposure containing benzene

Work in factory workshop with ambient hydro-

carbon exposure

Cleaning heptane tank not containing benzene

Work in field – no exposure

ppm

time

The benzene concentration to which an employee is exposed to may fluctuate significantly throughout the day, depending on the activity. A case study.



The measurement strategy chosen by a facility safety officer depends on three key factors: • Measurement quality corresponding to the safety level required, based on the risk assessment. The way results are displayed, the accuracy of the indicator and the required selectivity determine this quality.

9

Costs

Gas detection tubes with pumpExample device: Dräger-Tubes® with Dräger accuro

Measurement devices for sum measurements and se-lective measurements of VOCsExample device:

Dräger X-am® 8000 c

Laboratory b PID with gas chromatographExample device: Dräger X-pid® 9500

5 K

10 K

20 K

30 K

Costs for 50 measurements/year a



a) Cost for 50, 200 and 500 measurements result from purchasing costs/year + number of measurements x costs per measurements, see comparison of measuring methodsb) Example for laboratory costs by external servicec) Example: Selective measurement, as necessary for 50% of the use cases

Gas detection with MicroTubes & AnalyserExample device: Dräger X-act® 7000 with MicroTubes (based on set of 10 measurements = 150 €)

40 K

Cost comparison of measurement devices in relation to use frequency

• Measurement convenience when carrying out the measurements, for instance, how many steps are necessary before data is available on site, and if the operation is fail-safe.

• Use-frequency of the devices, which determines the cost per measurement. Higher procurement costs can pay off fast when they are calculated against cost per ongoing use.



What is the relative cost between tubes and laboratory clearance methods?

A sample calculation from a petrochemical plant in Germany: Assumption: Plant with 15 measurements per day at an exposure limit of 1 ppm, calculated on 230 working days per year. Measurement strategy for clearance in EU and ROW: Pre-test with Dräger X-am® 8000 (PID) whereby approximately 20% of the measurements were followed by a selective measure-ment of benzene (this can be a Dräger-Tube® for benzene or a pre-tube for the X-am® 8000) compared to measurements only in the laboratory or alternatively the use of Dräger X-act® 7000 with MicroTubes.

Pre-test measurement

strategy with PID +

selective with tubes +

laboratory testing. Total

amount consists of 15

PID tests for 0.50 €, 4

tests with tubes for 7.50

€, 3 lab tests for 30 € on

230 days.

All clearance measure-

ments for

benzene in the laboratory.

Total amount: 15 laborato-

ry test at a

rate of 30 € on 230 days.

Measurements with

Dräger X-act 7000 +

MicroTubes. Total amount:

15 measurements at a

rate of 19 € + 1 lab test

for 30 € on 230 days.

€

100,000

50,000

Precise and cost efficient

Combined measurement methods offer cost savings In practice, companies usually require different measurement tasks. 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 – es-pecially 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 inno-vative PID with integrated gas chromatograph.

Use frequency as a decision-making factorFor companies needing to measure benzene frequently (around 500 measurements per year) and with facilities with high risk of benzene contamination, a gas detection device with a PID sensor with a pre-test function is recommended, as it allows for selective re-peat measurements on a case-by-case basis. In our cost comparison chart, every second measurement was selectively verified. Further-

more, the use of a selective PID gas measurement device with an integrated gas chromatograph is particularly efficient in such a case because no additional costs are accrued with each measurement thereafter. At the same time, safety levels are improved because each selective measurement can be carried out easily and quickly to laboratory standards of quality.With average use (around 200 measurements per year) a measu-rement device with a PID sensor is also appropriate. Pre-tests and selective tests are rolled into one work step. This can bring potential savings when compared to exclusive, selective measurements. With the need for very high precision and convenience, an analyser with MicroTubes is an attractive alternative because, to some extent, it can spare the need for laboratory analysis. With low-use frequencies (around 50 measurements per year),selective tests with detection tubes, plus occasional complementary laboratory tests to ensure measurement accuracy, are an approp-riate measurement method. Supplemental, non-selective, pre-test devices with high ease-of-use are a viable alternative.



Convenience of measurement tasks and digitalisationCosts are an important factor in deciding on the measurement me-thod, but other criteria are coming more into focus. Besides the fact that measurement results should be reliably available, even at very low concentrations, 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 re-sult from digital data transmission. This speeds up documentation processes significantly and simplifies analysis.Another decision-making factor for improving both safety and effici-ency is if the same measuring solutions can be used for measuring other hazardous substances, besides benzene.Newer, innovative measuring systems thus open up new perspecti-ves for the safe handling of carcinogenic and other hazardous subs-tances to ensure both efficiency and safety in the industry.

Personnel protection, training and healthmonitoringGuarding workers from the harmful effects of benzene is the top priority for health and safety managers. Besides providing staff and contractors with the appropriate training and PPE, companies must ensure any workers potentially exposed to benzene have access to regular health checks. Biomarkers include blood tests revealing recent or sudden drops in white blood cell counts as an indication of benzene exposure with long-term health implications. Besides recent RAC official proposals to lower WEL for benzene, is the potential intro-duction of biological limit values of 0.7 μg benzene/L urine and 2 μg SPMA/g creatinine6. The main focus of the Dräger X-pid® is to make carcinogens more visible. By recording exposure values measured over a working day, the benzene concentrations a worker was exposed to can be documented and analysed. This is valuable information for occupational health and safety managers and industrial hygienists in addi-tion to the required biomarker test results.

strategies for measuring benzene

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