Below the PEL, Above the TLV: Mixed Solvent Exposure in Laminating
An adhesive-laminating department employs 22 workers on two 10-hour shifts. Full-shift personal samples on six workers show toluene at an 8-hour TWA of 38 ppm and xylene at 31 ppm; a 15-minute task-based sample during drum changeover peaked at 96 ppm toluene. The company's exposure limit table lists only the OSHA PEL of 200 ppm for toluene. Six workers report recurring headaches and two report dizziness over the last month; three have visible dermatitis on their forearms, and they immerse gloved hands in solvent to clean rollers. Local exhaust ventilation exists on two of five lines; the rest rely on roof exhausters and open doors. An office adjacent to the department complains of odor. The plant has never done a formal exposure assessment, and no medical surveillance program exists. A new production manager wants to know whether he has a problem, given the numbers are well under the legal limit.
1. How do you answer the production manager? Interpret the results against both the OSHA PEL and the ACGIH TLV, and explain what the peaks and the dermatitis indicate.
Read the worked answer
He has a problem, and the PEL comparison is the weakest available test.
TWA comparison. 38 ppm toluene is 19% of the 200 ppm PEL - but roughly 1.9 times the ACGIH TLV of 20 ppm. The xylene result of 31 ppm is well under both its PEL (100 ppm) and TLV (100 ppm). Under a PEL-only view, nothing is wrong; under a health-based view, toluene alone is already over the recommended limit.
Mixture effect. These solvents share a target organ and act additively. Apply the mixture formula: 38/20 + 31/100 = 1.9 + 0.31 = 2.21. A ratio above 1 means the combined exposure exceeds the limit even though no single component does. This is the finding the PEL table hides entirely.
Peaks. 96 ppm for 15 minutes during drum changeover exceeds the ACGIH excursion limit, which caps short-term excursions at three times the TLV (60 ppm for toluene) with a maximum of four per shift. Excursions of this size are typically where acute symptoms originate.
Extended shift. Ten-hour shifts require a shift-adjusted TLV; the allowable 8-hour value does not apply unchanged across a longer exposure period.
Dermatitis. Both solvents carry skin notations. Immersing gloved hands in solvent defeats the glove and creates a dermal route that no air limit addresses. The dermatitis is the exposure assessment telling you the air sampling measured the wrong route.
2. What are the gaps in this exposure assessment, and what would you do next?
Read the worked answer
This is a spot sample, not an exposure assessment - six workers out of 22, one shift, one day, no defined exposure groups.
Next steps:
- Define similar exposure groups by task and line: line operators, changeover crew, roller cleaners, and the adjacent office. Sample each group, and include the least-senior worker on each task rather than the most practiced.
- Sample both shifts and the full 10-hour duration, using a validated method (NIOSH 1500/1501 for aromatic hydrocarbons) with field and media blanks.
- Capture short-term and peak exposures deliberately, timed to drum changeover, line startup, and cleanup, not grabbed opportunistically.
- Assess the dermal route directly - skin wipes, observation of work practice, and glove selection testing. Nitrile performs poorly against toluene and xylene; a laminated film or PVA glove is the appropriate candidate, and it must be verified against the actual product, not the catalog.
- Consider biological monitoring - urinary o-cresol or blood toluene for toluene, urinary methylhippuric acid for xylene - to confirm whether absorbed dose tracks the air results. Interpret against BEI values, and account for shift timing and creatinine correction.
- Sample the office to characterize the complaint quantitatively; odor is a poor exposure metric but a reliable indicator of containment failure.
- Document everything so the assessment supports respirator decisions, medical surveillance referrals, and any future 1910.132 hazard assessment.
3. Recommend controls in priority order, and address medical surveillance and the office odor complaint.
Read the worked answer
Engineering first, because the high-exposure tasks are stationary and enclosable.
- Extend local exhaust ventilation to all five lines, designed with capture velocity at the source and a hood geometry that does not pull contaminated air across the worker's breathing zone.
- Replace open roller cleaning with an enclosed wash station or dedicated parts washer. This single change removes the dermal immersion and most of the peak exposure.
- Evaluate substitution: a water-based or lower-aromatic adhesive would eliminate the hazard rather than control it. Test adhesion before committing; do not substitute a material with unknown toxicity without review.
Administrative. Reduce or rotate the 10-hour shift pattern for the highest-exposure tasks; formalize changeover procedures to keep drums closed and transfers closed-loop.
PPE. Appropriate laminated gloves verified against toluene and xylene, splash goggles, and solvent-resistant aprons. If respirators are used even intermittently, 29 CFR 1910.134 requires a full written program - medical evaluation, fit testing, training.
Medical surveillance. Not specifically mandated by a substance standard here, but the reported headaches, dizziness, and dermatitis justify referring affected workers for evaluation and establishing a baseline and periodic program. Document the rationale.
Office odor. Investigate as a containment and pressure-balance problem, not a comfort complaint. Fix the source; do not mask it with fragrance or rely on general dilution.