benzene measurement strategy - draeger.com · with benzene measurement, there is a difference...

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In the petrochemical industry, benzene vapours can hardly be avoided. Work-related cancer, on the other hand, can be. But it requires precise monitoring of exposure to benzene using the right measurement strategy.

Benzene measurement strategy


BENZENE MEASUREMENT STRATEGY

Precisely identifying benzene in even low concentrations Knowledge of the carcinogenic effect of benzene on the human body has grown in recent years. Public awareness of the topic has also grown – as have regulatory requirements for companies to protect employees against inhaling benzene vapors.

In the 1980s, threshold values of up to 50 ppm were permissible. Today, OSHA defines a permissible exposure limit (PEL) of 1 ppm (measured as a time weighted average – TWA). The limit recom-mended by NIOSH (Recommended Exposure Limit – REL) is clearly below that at 0.1 ppm (TWA). And in some countries, per-missible levels are even lower. In Germany, for example, the so-called ”risk acceptance concept” of TRGS 910 defines tolerable exposure at 0.6 ppm. In addition, the accepted exposure level is currently 0.06 ppm, but shall be reduced to 0.006 ppm in the future.

These strict guidelines pose a challenge for Health, Safety and Environment officers (HSE), since very few technologies are capable of reliably indicating these extremely low values. Ideally, HSE officers are already taking steps to avoid exposing their employees to carcinogenic materials where possible.

ALARMING RESULTS

In 2014, NIOSH conducted a field study in the fracking industry to examine the level of exposure of employees to benzene gases in the atmosphere.1 The results were as follows:

The results were as follows:

– 15 of the 17 samples exceeded a value of 0.1 ppm– Two samples reached more than 0.5 ppm– During certain work, the 15-minute median values of

1 ppm were regularly exceeded– At open hatches, peak concentrations of up to

200 ppm were measured– An Ex measurement device showed up to 40% of the

lower explosion limit of a hydrocarbon gas concentration

FACTS & FIGURES

Benzene

Formula: C6H6

Identifiers: CAS 71-43-2, Label required: Flammable liquidExplosion limits, % by volume: LEL: 1.2; UEL: 8.6Health rating (NFPA): 3 (dangerous)Odor threshold: 0.78 ppmHealth effects: Eye, nose and respiratory tract irritation leading to headache, dizziness, convulsion and coma.

Chronic: Cancer (leukaemia)



LIMIT VALUES FOR BENZENE

Region Organisation/directive Values: TWA Values: STEL

USA OSHA (PEL)2 1 ppm 5 ppm

USA NIOSH (REL)2 0.1 ppm 1 ppm

EU (recommendation) RAC3 0.05 0.05

Germany (acceptance limit) TRGS9104 0.06 ppm 0.06 ppm

Germany (tolerance limit) TRGS9104 0.6 ppm 0.6 ppm

Key:

PEL – Permissible exposure limit

REL – Recommended exposure limit

RAC – Committee for Risk Assessment

STEL – Short-term exposure limit (15 min)

TWA – Time-weighted average (8-hour shift)

State: 11th January 2019

Different measurement tasksMeasuring benzene in the workplace can involve very diverse tasks, such as clearing a tank for maintenance work, measuring the average contamination of a work area, or checking the level of temporary peak exposure values. Furthermore, different companies implement regulations very differently. While some companies clear all work areas once a year, others examine individual work steps and at- tempt to precisely locate peak exposure sites. The goal is to make these critical work steps safer through the use of technical and organizational methods – and even additional breathing protection.

Balancing quality, time, and costThree criteria determine the selection of measurement methods: quality, time, and cost.

Quality pertains to the precision of the measurement results. Does the benzene concentration need to be measured selectively or is it sufficient to determine the sum value of all hydrocarbons in the air?

The factor of time is becoming increasingly important due to the pressure to increase efficiency. The faster a method delivers reliable results, the sooner work may continue after clearance. An important advantage of on-site measurements versus laboratory evaluation is the time that is saved – since evaluation is possible directly at the task location, where further measures may be decided upon.

In terms of cost, the number and frequency of measurements that need to be completed play a central role. Detector tubes, for example, offer an economical solution. The purchasing costs are low, and there are nearly no maintenance costs. However, if a com-pany performs many measurements at a continuous rate, reusable solutions are more affordable.



that is in contact with the surrounding air. If the exposure of a person needs to be monitored, then a passive collector is fastened to the clothing at the inhalation area. Due to the relatively low concentrations of substances in the air of interior rooms, sampling times from one day to several weeks may be required to identify substances in the relevant concentration range. The badge is evaluated in the labora-tory, while the collected substances are evaluated selectively. In any case, only average values may be recorded and exposure peaks are included in the average value.

Detector tubesSuitable for clearance, spot measurement, leak searchesDetector tubes can be used to detect benzene precisely, quickly, and economically. The new 0.25/a Dräger-Tube® measures to the lowest concentrations above 0.25 ppm. Measuring benzene using detector tubes is fast and simple. The tubes can easily be operated by non-experts using a hand pump – even in Ex areas. That‘s why detector tubes are suitable for air analysis in tanks and containers and for detecting leaks. It is also possible to use them for measuring con-taminations in certain work areas and detecting peak concentrations.

Photo-ionization detection Suitable for clearance, workplace monitoring, spot measurementPhoto-ionization detectors are ideal for locating hydrocarbons – es-pecially if they are present in very low concentrations. However, they cannot measure benzene selectively. Therefore, if a critical hydrocar-bon level is detected after a sum-measurement reading of the PID sensor, a subsequent selective measurement is needed to make it clear exactly which carcinogenic substance accounts for the highest proportion of the overall concentratio.

One advantage of PID devices is their ability to measure continuously and 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 certain work steps. Due to the various use cases the higher cost of the devices compared to other measuring methods quickly get amortized.

With benzene measurement, there is a difference between selective and non-selective methods. Isolated evidence can be gained from detector tubes, chips and diffusion collectors, as well as from labo-ratory results. Photo-ionization detectors (PID), on the other hand, only measure the sum of all volatile hydrocarbons in the air. There-fore, 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 your company’s requirements on quality and conveni-ence various measuring methods are possible.

Laboratory measurementSuitable for clearance, workplace monitoring, spot measurementIn spite of a relatively high time and cost investment, laboratory measurement is widely popular, since most field measurement methods are limited in terms of selectiveness and precision (see over-view). In the laboratory, on the other hand, extremely low or high concentrations can be determined reliably. This requires on-site sampling, which normally involves a pump and a suitable collection medium. The analysis itself in many cases is carried out by a gas chromatograph. The waiting time for results depends on how well the transfer of the sample to the laboratory is organized. The evaluation itself can usually be completed quickly.

Passive collectorsSuitable for workplace monitoringPassive or diffusion collectors (so-called ”badges”) consist of a collec-tion medium, such as active charcoal,) and a strip positioned before it

OVERVIEW: ADVANTAGES AND LIMITATIONS OF VARIOUS TECHNOLOGIES



DECISION SUPPORT: WHICH MEASUREMENT STRATEGY IS SUITABLE FOR WHICH PURPOSE?

Method Laboratory Gas detection tubes with pump

Measurement devices for sum measurements and selective measurements of VOCs

PID with gas chromatograph

Example device Dräger-Tubes® with Dräger accuro

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

Selective Measurement possible?

Yes Yes In combination with benzene selective tube

Yes

Measurement range Practically unlimited 0.1 ppm or 1 to 2,000 ppm From 0.05 to 2,000 ppm (depending on sensor type), gas: isobutene

On-site application possible?

No Yes Yes Yes

Time factor Several hours 5 minutes 5 minutes (incl. selective tube measurement)

1 minute

Cost range at all Very high Low Low High

Procurement costs3 None (if used as external services)

LowPump: Dräger accuro-Set: approx. 300 €

AverageDräger X-am® 8000 with Ex-, O2-, CO-, H2S- and PID sensors: approx. 3,000 €4, incl. charging device

HighDräger X-pid® 9000/9500: approx. 18,000 €4

Costs per measurement5

Very high, approx. 70 € Average – depending on useCost per tube: 5–10 €Time needed: 4–8 minutes -> 4 €Assumption: 10.50 €6 per measurement on average

LowAssumption: 6.58 € per measurement on average7

Very lowAssumption: 0.66 € (only labour costs)

Specifics Very precise substance-specific measurement

Good measurement quality, selective measurement

Fast as pre-test Accurate readings in low range, selective,immediately available onsite, easy to use

Further aspects Error potential while sampling

Training required, thus higher costs for service providers

Requires practice, several minutes needed per measurement disposable items required.

Outside influences, such as temperature and humidity, affect measurement resultsError potential in reading data

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

Training needed. Maintenance and preparation steps necessary.

Digital data transfer possible

Maintenance and preparation steps necessary

Evaluation of measurement quality in total*

10 5 6 9

Evaluation of measurement convenience in total8

1 5 7 10

*On a scale from 1-10. 10 = very high; 1 = very low



Solution: Combining different methods intelligentlyThere are different new ways of putting this into practice.

For clearance of areas such as tanks and other confined spaces PIDs with pre-installed tubes, detection tubes with a pump, and also selective evaluation of benzene in measurement laboratories are all suitable.

The combination of a PID with a detection tube is a cost-effective method. One method is to use a gas detection device with a PID-sensor that can utilize 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 of 10 ppm during the pre-test, then selective measurement in a second step measures the ben-zene value using a pre-tube for the PID or single detection tubes. Such a pre-tube acts like a filter that holds back all hydrocarbons except benzene. Only benzene is passing through the pre-tube, therefore the PID can give a benzene-specific reading. With this method, the result is available after a few minutes.

The advantage of this process is fast results, which enable safe decisions and improve cost-effectiveness through the use of specific tubes.

Innovative: Combining pre-tests with the analysis by a gas chromatograph Another innovative method is to substitute the measurement by the use of a PID-sensor with an integrated gas chromatograph. This device combines pre-tests with selective tests, therefore simplifying and shortening measurement processes. Two measuring modes, one broadband measurement in scan mode and one selective measurement in analysis mode, eliminates the need to carry out manual tube tests and increases safety through laboratory-quality measurement results. It incurs higher procurement costs – but at a high frequency of use, when broken down per measurement, this could be worth it.

Using a multigas detector for this application gives you the ad-vantage of purchasing, servicing, training and transporting only one detector in the field which serves all of your purposes such as clearance measurements for confined space entry, leak search and benzene readings.

Selective measurement with tubes or pre-installed tubes may be omit-ted if the overall contamination by hydrocarbons is sufficiently low.



Selective measurement

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

then another selective measurement for benzene is taken, e. g. a PID with a pre-installed tube or in

the analyse mode with the Dräger X-pid®.

Monitoring

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

Random samples

Regular laboratory analysis of random 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®.

Reliable workplace monitoring The amount of benzene to which employees are exposed during a shift depends on their activities and the resulting concen-trations involved. In the petrochemical industry, contamination levels often show significant 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.

After successful clearance measurement of an area which has been classified as hazardous for exposure to benzene continuous monitoring of the work area has to take place.

Continuous area monitoring can be achieved through use of gas detection devices with a non-selective PID-sensor positioned in the work area. They quickly react to changes in concentration and imme-diately indicate if limits are exceeded. The alarm threshold is adjusted depending on the limit value. When an alarm is activated, work must stop immediately. Another advantage of PID devices is data recording: All measurement values are stored for later analysis.

Because of the non-selectivity of the PID-sensor, regular selective spot measurements should also be carried out for control. Their fre-quency depends on precise risks in accordance with risk evaluations, which also determines the preferred measurement methods. In prin-ciple, 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 period (normally an 8-hour shift), or a series of sequential samples taken by spot measurements every 30 minutes should be carried out.

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 will be inhaling. The US Department of Health and Human Services recommends that at least three samples of 15 minutes duration each should be taken6. The sample with the highest value is given as the maximum concentration.

FEATURES OF DIFFERENT MEASUREMENT TECHNOLOGIES



CHANGING CONTAMINATION

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

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

Interim conclusionThe measurement strategy chosen by a facility safety officer depends on three key factors:– The measurement quality, which is oriented to the level of safety

desired based on the risk assessment. The way the results are displayed, the accuracy of the indicator and the required selectivity determine the quality.

– The measurement convenience when carrying out measurements. This includes the number of steps, how fast data is available onsite and whether operation is fail-safe.

– The 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.



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® 8000c

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

5 K

10 K

15 K

20 K

25 K

30 K

35 K Costs for 50 measurements/yeara

Costs for 200 measurements/yeara

Costs for 500 measurements/yeara

LEGEND: a) Cost for 50, 200 and 500 measurements result from purchasing costs/year + number of measurements x costs per measurementsb) Example for laboratory costs by external service c) Example: Selective measurement, as necessary for 50% of the use cases

With average use frequency (ca. 200 measurements/year) a measurement device with a PID sensor is also appropriate. Pre-tests and selective tests are rolled into one work step. With relatively frequent readings, this can bring about potential savings when compared to exclusive selective measurements.

With low use frequency (around 50 measurements/year), selective tests with detection tubes, as well as occasional complementary laboratory tests to ensure measurement accuracy, are an appropriate measurement method. Supplemental non-selective pre-test devices with high ease-of-use are a viable alternative.

CHOICE OF MEASUREMENT DEVICES IN RELATION TO USE FREQUENCY



Combination of measurement methods offers 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. In other words, it is ideally suited to 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 comfor-table and quickest way to measure benzene concentrations under 1 ppm is an innovative PID with integrated gas chromatograph.

Decision support: Use frequency as benchmarkFor companies with high benzene measurement needs (upwards of ca. 500 measurements/year) and facilities with high toxic risk from benzene, the use of a gas detection device with PID sensor with a pre-test function, offering implementation of selective remeas- urements on a case-by-case basis is recommended. In our example, every second measurement was selectively verified. Furthermore the use of a selective PID gas measurement device with an inte-grated gas chromatograph is particularly efficient in such a case, because no additional costs are accrued with each further measurement. At the same time, safety levels are improved because each selective measurement can be carried out easily and quickly to laboratory standard quality.

With average use frequency (ca. 200 measurements/year) a meas-urement device with a PID sensor is also appropriate. Pre-tests and selective tests are rolled into one work step. With relatively frequent readings, this can bring about potential savings when compared to exclusive selective measurements.

With low use frequency (around 50 measurements/year), selective tests with detection tubes, as well as occasional complementary laboratory tests to ensure measurement accuracy, are an appropriate measurement method. Supplemental non-selective pre-test devices with high ease-of-use are a viable alternative.

Pre-test measurement strategy with PID, selective with tubes + CMS; laboratory testing. Total amount consists of 15 PID tests for 0.46 €, 4 tests with tubes for 6.25 €, 3 lab tests for 30 € on 230 days.

All clearance measurements for benzene in the laboratory. Total amount: 15 laboratory test at a rate of 30 € on 230 days.

€

100,000

50,000

Precise and cost efficient

What is the relative cost between tubes and laboratory clearance methods?Here is a sample calculation from a petrochemical plant in Germany:– Assumption: Plant with 15 measurements per day at OSHA-PEL

(1 ppm) calculated on 230 workdays per year– Measurement strategy for clearance in EU and ROW: Pre-test

with Dräger X-am® 8000 (PID) at a rate of 0,46 € per test, whereby approximately 20% of the measurements were followed by a selective measurement of benzene at a rate of 6,26 € per tube measurement (This can be Dräger-Tube® for benzene or a pre-tube for the X-am® 8000 for selective measurement.)

– Only 20% of all clearances are checked with random samples in the laboratory (at a rate of 30 € per test).



IMPRINTGERMANYDräger Safety AG & Co. KGaARevalstraße 123560 Lübeck

www.draeger.com

1 Esswein, E., Snawder, J. King, B. et al. Preliminary Field Studies on Worker Exposures to Volatile Chemicals during Oil and Gas Extraction Flowback and Production

Testing Operations. Niosh Science Blog. https://blogs.cdc.gov/niosh-science-blog/2014/08/21/flowback-2/ (retrieval: 11/01/2019)

2 https://www.cdc.gov/niosh/idlh/71432.html (retrieval: 11/01/19)

3 https://echa.europa.eu/de/-/committee-for-risk-assessment-recommends-an-occupational-exposure-limit-for-benzene (retrieval: 11/01/2019)

4 https://www.dguv.de/ifa/gestis/gestis-stoffdatenbank/index.jsp (keyword: “benzene“; retrieval: 11/01/2019)

5 A tube measurement takes in average 6 minutes => 4 € labour costs

6 Occupational Safety and Health Guideline for Benzene. https://www.cdc.gov/niosh/docs/81-123/pdfs/0049.pdf (retrieval: 11/01/19)

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