PEL Permissible Exposure Limit
STEL Short-Term Exposure Limit
TLV Threshold Limit Value
TWA Time-Weighted Average

Chain of Custody

IMPORTANT NOTE: Masking tape is not a suitable seal for our samples. Currently, KYOSH administration does not make available appropriate chain of custody seals, directing CSHOs to use masking tape. Any company who would challenge the viability of our samples in court would more than likely be successful if the samples were not within direct view of the CSHO who performed the sampling or a CSHO counterpart; or were kept within another tamper-evident container when not in direct view of these individuals.


The following items should be marked on the chain of custody labeling for each sample obtained in the course of an inspection:

  • Name of company
  • Optional Report No. and/or Federal Inspection No.
  • Sample No.
  • Date



  • TWA Concentrations — This is the average concentration of a particular hazardous substance over eight (8) hours* of a work shift.
    • This eight-hour period need not be consecutive. For example, for a 12-hour shift, if the highest concentrations occurred during the first two hours and the last six hours, those can be the only concentrations considered. (Please refer to OSHA Technical Manual, Section II, Chapter 1, III.,

Sampling Sheets

On sampling sheets, such as the OSHA-91(S), ensure that both the PEL and the lower exposure limits, such as Action Levels, are noted. This provides the lab with direction on how precise the results must be.

  • There was an incident in the 2010s where KYOSH was informed by CHFS Central Laboratory that formaldehyde analyses performed on years' worth of KYOSH-submitted formaldehyde samples were not precise enough to determine if the Action Level had been breached. All the companies where formaldehyde sampling had been performed during those years had to be informed of the inadequacy of the sampling results. It would be best to avoid these situations in the future. Noting not only the PELs but the Action Levels also on our sampling sheets help prevent such situations.


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Pages in category "Sampling"

The following 5 pages are in this category, out of 5 total.