Permissible exposure limits

The American Conference of Governmental Industrial Hygienists has set new recommendations around lower hydrogen sulfide (H₂S) monitoring, and I have heard that OSHA may consider doing the same. How will these changes impact my gas monitoring program and safety audit?

Responding is Andrew Saunders, applications and training specialist, Honeywell Analytics, Lincolnshire, IL.

Since ACGIH lowered its threshold limit value for H₂S, gas detection manufacturers have introduced monitors to comply with this new recommendation. However, there has been significant reluctance to this change from groups that typically use the more strict recommendation in Canada and the state of California. Moreover, this new recommendation is a challenge for current sensor technology in which instability across temperature, humidity and pressure may result in nuisance alarms even if no H₂S gas is present. The problem is that the change was by a factor of 10 – 10 parts per million down to only 1 ppm. Still, today OSHA’s time-weighted average for H₂S remains at 10 ppm and short-time exposure limit at 15 ppm, according to the NIOSH Pocket Guide to Chemical Hazards.

OSHA permissible exposure limits are decades old, and something recently occurred that may cause the agency to re-evaluate its current standards. According to a recent Wall Street Journal article, OSHA has fined a company under the General Duty Clause for worker exposure to styrene even though the exposure was below OSHA’s PEL for styrene. OSHA has released an annotated table for PELs, admitting that its current standards are outdated and may be inadequate for ensuring worker safety. This table provides a side-by-side comparison of OSHA, NIOSH and ACGIH limits. Furthermore, OSHA states, “OSHA’s mandatory PELs in the Z-Tables remain in effect. However, OSHA recommends that employers consider using the alternative occupational exposure limits because the Agency believes that exposures above some of these alternative occupational exposure limits may be hazardous to workers, even when the exposure levels are in compliance with the relevant PELs.”

The bottom line is that it is up to each company to ensure a safe workplace. Information on standards, guidelines and recommendations, as well as proper training, is key to making sure everyone returns home safely after a hard day’s work.

Editor's note: This article represents the independent views of the author and should not be construed as a National Safety Council endorsement.