Benzene: which of OSHA's two limits applies to you

This page explains what the rules and common practice call for. Every site is different, and what a survey or a filing needs at your facility is something we work out with you after we see it.

Benzene appears twice in OSHA's standards, with limits that are ten times apart. Which one applies to you depends on what part of industry you are in.

The number everyone quotes is 1 part per million (ppm). That is the permissible exposure limit (PEL) in OSHA's benzene standard, as an 8-hour time-weighted average (TWA).

The benzene standard excludes several kinds of work, however. For those, benzene falls back to its entry in OSHA's general air contaminant limits, in Table Z-2. That entry is 10 ppm as an 8-hour TWA, a 25 ppm acceptable ceiling, and a 50 ppm acceptable maximum peak above the ceiling.

Neither number applies to everyone. Calling 1 ppm “the” benzene limit ignores the part of the standard that says who it covers, and a drilling company that assumes 10 ppm applies across its whole business has made the same mistake in the other direction.

Which standard applies to you

The kinds of work excluded from the benzene standard, and left under Table Z-2, include:

• Oil and gas drilling and well servicing
• Coke oven operations
• Sealed, intact containers and transportation pipelines. Separately, containers and pipelines that carry mixtures with less than 0.1% benzene, plus natural gas processing plants below 0.1%.
• Certain bulk loading and transfer operations
• Handling gasoline after it leaves bulk wholesale storage, which means service stations and distribution. There is one exception: work that dispenses gasoline or motor fuels more than 4 hours per day at an indoor location stays covered by the benzene standard.

This distinction matters a great deal. A company can have one site under the 1 ppm standard, with its action level, medical surveillance and regulated areas, and another site under Table Z-2 at 10 ppm with none of those provisions.

You cannot apply one set of requirements across both. The first question in planning a benzene survey is which standard covers you, and the answer should be in writing.

Exposure limits

The benzene standard also sets a short-term exposure limit (STEL), and at or above its action level it requires periodic monitoring. The last row of the table is NIOSH's recommended exposure limit (REL).

Where we find it

• Petroleum refining and terminals
• Petrochemical manufacturing
• Coke ovens and by-product recovery
• Rubber and tire manufacturing
• Solvent and adhesive blending
• Laboratory chemical use
• Tank cleaning and confined space entry where the equipment holds hydrocarbons
• Gasoline distribution and marine loading

Tank entry and tank gauging are the exposures that get missed. They are short and intermittent, and they are not on the shift schedule anyone hands the consultant on arrival.

How we sample for it

Note the sampling time: 12 liters over 240 minutes is four hours, not eight. A full-shift TWA therefore takes consecutive tubes, changed mid-shift, with the results weighted by air volume.

Suppose a survey hangs one tube on a worker at 7 a.m. and collects it at 3 p.m. That pulls twice the recommended air volume through the tube, and the risk is breakthrough, where benzene moves past the front section and out of the tube completely. The laboratory will report the back section, and if it is loaded, your result shows only that the exposure was at least that high. It is not a true measurement.

The risk of breakthrough rises with humidity and with other solvents. Refinery and tank-cleaning air often contains toluene, xylene, hexane and heavier hydrocarbon vapors, all competing for the same sites on the same charcoal. In heavily loaded air the sample volume has to come down, which means more tubes, not fewer.

That is the real cost driver on a benzene survey. The driver is not the laboratory work, because the analysis of charcoal tubes is not expensive, but the tube count. A defensible full-shift result on a process with heavy solvent vapor may take two or three tubes for each worker. Separate short-term tubes for the STEL come on top of that.

→ How many air samples do you really need?

What your results require you to do

This is where people get caught. Benzene does not follow the 6-month and 3-month pattern that people carry over from silica and hexavalent chromium.

Set those two rows beside the silica standard and the difference is plain. Benzene's schedule above the PEL is the same as silica's schedule at the action level: above the PEL, benzene asks for six months where silica asks for three.

That is not a license to relax. It means the monitoring schedule is not what protects your workers from benzene, because other provisions of the standard do that: regulated areas, respirators and medical surveillance. A benzene program built only around the monitoring calendar is thin, and it is thin because of how the standard is designed, not because anyone missed something.

→ How often OSHA requires air monitoring, by substance

The number below the number

The NIOSH REL is 0.1 ppm, which is a tenth of the OSHA PEL and a fifth of the action level. Benzene is a recognized human carcinogen, and the cancer is leukemia.

Most of the gaps between limits on this site come from different ways of measuring, but this one does not. Both are time-weighted averages over a work shift, with OSHA's covering 8 hours and NIOSH's covering up to 10, and the two are ten times apart.

We will report your results against both. If a result lands between 0.1 and 1 ppm, you meet the OSHA PEL but you are not where NIOSH would put you. You should hear that from us and not from the other side's lawyer.

→ OSHA PELs compared with recommended limits