Benzene Monitoring at Refineries: Pairing Tiger Select and Titan 2 from Walkdown to Fixed Monitoring

Benzene is one of the few substances at a refinery where a measurement error means not product loss but a direct risk to workers' health. It is a recognised carcinogen, and permissible workplace concentrations are orders of magnitude lower than for most hydrocarbons. And benzene is almost never alone: it comes mixed with toluene, xylenes, hexane and dozens of other compounds.

Hence the core problem: a standard photoionisation detector shows total volatile organic compounds and cannot say how much of that is benzene. Below is how Ion Science Tiger Select and Titan 2 solve this, and how to build a monitoring system on site.

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Why benzene is a separate task

Low exposure limits

Benzene limits vary between countries, but they are all very low:

Limit	Value	Conversion
Russian workplace limit, shift average (used as a reference in some CIS countries)	5 mg/m³	≈ 1.6 ppm
Russian workplace limit, short-term maximum	15 mg/m³	≈ 4.7 ppm
EU binding limit (Directive 2004/37/EC as amended by 2022/431), from April 2026	0.66 mg/m³	0.2 ppm

Conversion: mg/m³ = ppm × 78.11 / 24.45 (at 25 °C), so 1 ppm of benzene ≈ 3.2 mg/m³. Kazakhstan has its own hygiene standards; check the current edition and your corporate standards for your site (many international operators apply stricter internal limits).

Note that we are talking about single ppm and fractions of a ppm. A flammable gas detector set to LEL does not see benzene at these levels: benzene's lower explosive limit is about 1.2% vol, so 1% LEL is roughly 120 ppm, dozens of times above the exposure limit.

A mixture, not a pure substance

A PID with a 10.6 eV lamp ionises benzene (ionisation potential 9.24 eV), but it equally ionises toluene, xylenes and most heavy hydrocarbons. A reading of "5 ppm" over an open hatch on a gasoline tank could mean 0.1 ppm of benzene or 3 ppm of benzene. A work permit decision cannot be made on a total reading alone.

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How Tiger Select measures selectively

Tiger Select is a portable PID from the Tiger range with two modes:

1. TVOC mode: total volatile organic compounds, like a standard Tiger. Used for rapid screening.
2. Select mode: measurement of benzene (or total aromatic compounds, TAC) using a single-use selective pre-filter tube. The tube retains interfering compounds and lets the target substance through to the sensor. The result is the concentration of benzene specifically.

The practical workflow:

• the operator walks the area in TVOC mode, which is fast and uses no tubes;
• if TVOC exceeds the level at which benzene could exceed the limit, a tube is fitted and a selective measurement taken;
• the result is logged in the instrument with location and time.

This two-step approach saves consumables and time: a selective measurement is needed only where the overall background calls for it.

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Where a fixed Titan 2 is needed

A portable instrument shows the picture at the time of the walkdown. But there are zones where benzene can appear at any moment and where people are present constantly or regularly:

• loading and unloading points for gasoline, reformate and aromatic fractions;
• pump houses for aromatic products, with leaks through mechanical seals;
• sampling points and laboratory rooms near units;
• tank cleaning areas and drain systems.

These places call for a fixed selective monitor, Titan 2. It runs continuously without an operator and sends data to the DCS / SCADA. The key difference from a fixed total VOC PID monitor (Falco) is that Titan 2 measures benzene specifically, not the sum of compounds. Where the hydrocarbon background is high and benzene is what must be controlled, this is fundamental.

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A benzene monitoring system: four levels

Level	Task	Instrument	Who uses it
Area screening	Quickly find places with elevated VOC	Tiger XT / Tiger Select in TVOC mode	Gas rescue teams, walkdown operators
Selective measurement	Determine benzene concentration at a point	Tiger Select in Select mode	Gas rescue teams, HSE
Fixed monitoring	Continuously monitor permanent-risk zones	Titan 2	Automatic, signal to DCS
Personal protection	Warn an individual worker	Cub	Personnel in the zone

No level replaces another. A fixed monitor does not see a leak in the next pump house, a portable instrument does not work at night without an operator, and a personal monitor protects a person but does not find the source.

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Typical scenarios at a refinery or terminal

Permit for work inside a tank or vessel. Before opening and entry: a total VOC reading, then a selective benzene reading at several heights (benzene vapour is heavier than air and collects at the bottom). During work: personal monitors on people. More in the article on gas testing for confined spaces.

Aromatics pump house walkdown. TVOC screening at every mechanical seal and flange; on exceedance, a selective measurement and a seal repair request.

Loading rack. A fixed Titan 2 at operators' breathing height with an alarm to the control room; periodic checks with a portable instrument.

Fenceline environmental monitoring. Readings at the site boundary to confirm benzene is not leaving the site.

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Mistakes to avoid

• Treating TVOC as benzene. A total PID reading is a "check this" signal, not a benzene result.
• Converting TVOC using the benzene correction factor. A correction factor applies to a pure substance, not to a mixture of unknown composition. Details are in the article on PID correction factors.
• Skipping the bump test. An instrument not checked with gas before the shift may show zero with a dirty lamp. The routine is covered in the article on PID calibration and maintenance.
• Installing a fixed monitor "where convenient". The location is chosen by leak sources, air movement and where people are, not by proximity to a cable route.

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Summary

Benzene monitoring is a task where "roughly" does not work. A general PID finds problem areas, the selective Tiger Select gives the concentration of benzene specifically, the fixed Titan 2 covers permanent-risk zones, and the personal Cub protects the worker. Together they form a system you can show both to inspectors and to your own occupational safety team.

KEG TRK supplies Ion Science instruments in Kazakhstan and helps choose a configuration for your site: the number of portable and fixed instruments, installation points, consumables and a calibration routine. A general overview of PID technology is in the article on gas and VOC leak detection.