The Essentials of Hexavalent Chromium Sampling: A CIH's Guide
Hexavalent chromium, or Cr6+ is a highly regulated hazard in industrial hygiene with a strict permissible exposure limit (PEL) of just 5 µg/m³ for an 8-hour time-weighted average. This low limit makes meticulous sampling and analysis crucial, but it also means that seemingly small errors can have a big impact.
To get defensible results, Certified Industrial Hygienists (CIHs) must pay close attention to two critical details:
- Field blanks
- Holding times.
Overlooking these can compromise even the most careful sampling efforts and lead to misleading data.
The Must-Have: Field Blanks
Field blanks are not optional; they are a vital tool for ensuring the accuracy of your results. A field blank is a filter processed in the exact same way as a sample, but with no air drawn through it.
Why are they so important?
- Contamination Detection: They help you identify if any Cr6+ was introduced through reagents, filter media, or your handling practices.
- Analytical Baseline Control: The extremely low PEL means that even trace contamination from reagents or other common sources can appear as a positive detection, making it difficult to distinguish true exposure from background noise. Field blanks provide the evidence needed to separate real workplace exposures from these background artifacts.
- Regulatory Defensibility: OSHA inspectors expect to see field blanks in your sampling plan. Without them, it's nearly impossible to defend results that are close to the exposure limit.
The Clock is Ticking: Holding Times
sets clear holding-time requirements to prevent the degradation of Cr6+ during storage. Failure to meet these timelines can cause significant bias and make your data unreliable.
Here's a breakdown of the requirements for different operations:
- Welding operations: Samples must be analyzed within 8 days. Waiting longer can cause a loss or conversion of 10% or more of the Cr6+ which leads to an underestimation of the true exposure.
- Chromium plating operations: Samples must be analyzed within 6 days. In acidic or humid conditions, Cr6+ can convert to Cr(III), significantly reducing recovery over time. Acid-induced degradation can cause a loss of 10% or more after just six days. However, samples can be stabilized in the lab to extend the holding time up to 14 days.
CIHs must plan their sampling, shipping, and analysis schedules carefully to meet these deadlines or arrange for stabilization to prevent bias.
Partnering for Success
Ensuring the quality of your Cr6+ data hinges on more than just proper sampling. It requires strict attention to field blanks, adherence to holding times, and laboratory precision. This is where a partnership with an accredited lab becomes essential.
Eurofins Built Environment Testing can provide detailed field blank analysis to help you separate true exposures from contamination. We can also help ensure holding time compliance with fast turnaround times and stabilization options for plating samples. By partnering with an accredited lab, you get reliable, defensible data to make sound risk assessment and compliance decisions.