Chemical Exposure in a Degreasing Bay
A small manufacturer uses a solvent degreaser in an open bay. The safety data sheet lists a solvent with an 8-hour occupational exposure limit of 50 ppm and a short-term limit of 100 ppm. Air sampling during a typical 6-hour degreasing task gives 62 ppm as an 8-hour TWA, with a 15-minute peak of 140 ppm during parts transfer. The bay has a roof exhaust fan but no local exhaust at the tank. Workers wear nitrile gloves and safety glasses; one reports headaches and dizziness by mid-afternoon. The plant has no respiratory protection program, no exposure records, and no medical surveillance.
1. Interpret the sampling results and evaluate the current controls. What is the priority action?
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Both results exceed limits. The 62 ppm 8-hour TWA exceeds the 50 ppm limit, and the 140 ppm 15-minute peak exceeds the 100 ppm short-term limit by 40%. The peaks occur during parts transfer, which points to the task, not just the tank, as the source. Headache and dizziness are consistent with solvent exposure and should be treated as sentinel symptoms, not background complaints.
Current controls are inadequate: a roof exhaust fan dilutes and removes air from the space but does not capture vapor at the source; the open tank allows evaporation into the breathing zone. Nitrile gloves and safety glasses protect skin and eyes but not inhalation. There is no respiratory protection program, so respirators cannot simply be handed out; no exposure records means the organization cannot demonstrate control or detect trends; no medical surveillance means health effects are found late.
Priority action: reduce exposure at the source. Add local exhaust ventilation at the tank, cover the tank when not in use, and enclose or automate parts transfer to eliminate the peak. Re-sample after controls. Until exposure is controlled, implement interim measures with a proper respiratory protection program if respirators are used.
2. The plant proposes handing out half-mask respirators with organic vapor cartridges to everyone in the bay. What are the requirements and limits of that approach?
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Respirators are a last line of defense, not a substitute for source control, and handing them out without a program creates new risk. Requirements include: written program with a designated administrator; medical evaluation before fit testing; fit testing for each wearer and respirator model; training on use, limitations, and cartridge change; cartridge change schedules based on use conditions; storage, inspection, and maintenance; and recordkeeping.
Limits: a half-mask with organic vapor cartridges has an assigned protection factor that caps the concentration at which it may be used; at 140 ppm peaks the margin may be thin, and the cartridge must be appropriate for the specific solvent. Cartridges have finite capacity and breakthrough can occur without warning; a change schedule is required. Facial hair at the seal, poor fit, and user discomfort reduce protection. Respirators do not protect the eyes or skin from vapor, and they do nothing for the source.
The correct sequence is engineering control first, then administrative measures, then respiratory protection as an interim or supplementary measure with a full program. Re-sampling should confirm the controls work.