Hexavalent chromium: tight limits and easy-to-ruin samples
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.
Hexavalent chromium, also written Cr(VI), is one of the few substances where the sampling is easy to get wrong, and getting it wrong is expensive.
The limits are tight. OSHA's permissible exposure limit (PEL) is 5 micrograms per cubic meter of air (µg/m³) as an 8-hour time-weighted average (TWA), and the action level is 2.5 µg/m³. At or above the action level, you have to continue monitoring.
Those are micrograms. For scale, that is roughly a thousandth of the limit, by weight, for many nuisance dusts. As a result, the smallest amount the lab can measure sits uncomfortably close to the levels you are trying to measure, and sloppy work in the field shows up directly in your results.
Where we find it
- Welding stainless and high-alloy metals. This is the most common source. The chromium in the base metal and filler is converted to hexavalent chromium in the arc. Mild steel welding largely does not produce it, so the same welder in the same booth with a different rod or wire has a completely different exposure.
- Hard and decorative chrome plating. Chromic acid mist rises from the tank.
- Chromate conversion coatings and chromate primers. These matter a great deal in aerospace work. Spraying chromated primers is a well-documented high-exposure task.
- Thermal cutting of stainless with plasma, laser or oxyfuel.
- Grinding and abrasive blasting on chromate-coated surfaces.
- Refractory brick and cement work that involves chromite.
How we sample for it
| Sampling media | Depends on the operation. A 5.0 µm PVC filter for welding, thermal cutting and painting. A quartz fiber filter coated with sodium hydroxide (NaOH) for plating, where a PVC filter would capture too little of the chromic acid mist |
| Analytical methods | OSHA ID-215 v2 · NIOSH 7605 (ion chromatography) · NIOSH 7600 |
| Sample type | Personal sample in the worker's breathing zone, for the full shift |
| Laboratory | A nationally accredited laboratory (accredited under the federal NVLAP program) |
Filter selection deserves a closer look, because it determines whether a result means anything. The OSHA method (ID-215 v2) specifies NaOH-coated quartz fiber filters with no binder for chromium plating, and 5.0 µm PVC for everything else.
PVC filters on a plating survey will still give you a number, but PVC captures too little of the chromic acid mist, so the number understates the exposure.
Storage time and handling matter more here than with most substances. Hexavalent chromium can convert to trivalent chromium on the filter before the laboratory analyzes it, which gives you a falsely low result. A low result you cannot trust is worse than no result, because you will act on it.
What your results require you to do
OSHA's hexavalent chromium standard sets out these steps:
- Initial result below the action level (2.5 µg/m³): you may stop monitoring those workers, with no second sample to confirm.
- At or above the action level, but at or below the PEL: repeat the monitoring every 6 months.
- Above the PEL (5 µg/m³): repeat the monitoring every 3 months.
- To stop after a periodic result below the action level: the result must be confirmed by another measurement taken at least 7 days later. The silica and beryllium standards say “two consecutive measurements 7 or more days apart” for the same idea, and in practice both mean two results below the action level, at least 7 days apart. What differs between standards is whether this applies to initial monitoring. Under the hexavalent chromium standard it does not.
- Notify workers within 15 work days, in writing or by posting the results.
The standard also has a performance-oriented option. It lets you characterize worker exposure using any combination of air monitoring data, historical monitoring data and objective data. If your data truly represents your operations, you may not need to sample at all, and we will tell you if that is your situation.
→ See how often monitoring is required, by substance
What the laboratory does not cover
A laboratory analyzes the sample it is sent. Its part is the chain of custody, the filter and the result.
The laboratory does not do the field half of the work. That half means someone in the plant at the start of the shift, fitting pumps to welders and recording which rod or wire was in use and whether the fume extraction was switched on. On an air monitoring survey, that is our part.
If you ever contest an OSHA citation, the case turns on that record as much as on the number.
Plan a hexavalent chromium survey
Ron Fleming has done this work himself since 1993. You talk directly to the person who does the job. No account managers. No call center. Our prices are well below the competition. Tell us what is going on and we will send a written scope of work and a price, at no cost.
Talk with us. No cost.References
The regulations and standards behind this page, with links to the official text, so you can check the source yourself.
- OSHA 29 CFR 1910.1026
- OSHA 29 CFR 1910.1026(d)(2) Chromium (VI)