Toluene on the Cementing Line: Air Sampling, Hippuric Acid and a Pregnant Worker
A shoe-assembly plant in Bogor employs 210 workers; 24 women work the cementing line, spreading toluene-based adhesive in a 9 × 12 m room with no local exhaust ventilation, two ceiling fans and louvred windows. Personal air sampling on two workers gave 118 ppm and 131 ppm as 8-hour TWA; the shift is actually 10 hours, six days a week. Twelve workers report headache and dizziness, and one had a brief loss of consciousness at the line last month. Half-mask respirators with organic-vapour cartridges are issued, but cartridges are kept in a warm cupboard, changed only 'when you can smell it', and no fit testing is done. Urinary hippuric acid from a local laboratory is reported as 'within normal limits' for all twelve. One worker is 14 weeks pregnant. The owner asks the doctor whether the air results are 'really over the limit' and whether giving the pregnant woman a better mask would be enough.
1. Interpret the exposure data. Are these workers over the NAB, and what correction is required because they work 10-hour shifts?
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Reasoning. The Indonesian NAB for toluene is 50 ppm (about 188 mg/m³) as an 8-hour time-weighted average - confirm the current figure in Permenaker 5/2018 and the earlier Permenakertrans 13/MEN/X/2011 list before putting it in a report. On that basis 118 and 131 ppm are 2.4 and 2.6 times the NAB even before any adjustment. The adjustment matters because the NAB assumes an 8-hour exposure with 16 hours for recovery. Using the Brief & Scala model, adjusted NAB = 50 × (8/10) × ((24−10)/16) = 50 × 0.8 × 0.875 ≈ 35 ppm. The measured concentrations are therefore roughly 3.4–3.7 times the limit that applies to this roster.
Caveats I would state. Only two workers were sampled on presumably one day; the '8-hour TWA' may have been calculated rather than measured over the full 10 hours. I would repeat full-shift sampling on the highest-exposed workers across a week, with an accredited laboratory, and also sample during glue pouring, when short-term peaks are likely to be far higher than the average. Toluene is also absorbed through skin, so air sampling alone underestimates dose.
Clinical corroboration. Headache, dizziness and a loss of consciousness are consistent with CNS effects at this level and make the exposure medically significant, not merely a compliance number. A loss of consciousness on the line also raises the possibility of a cardiac arrhythmia from solvent exposure.
Conclusion. Yes, clearly over the limit, and the 10-hour roster makes it worse, not better.
2. The laboratory reports hippuric acid as normal and the company treats this as reassurance. How should the physician evaluate the biomonitoring and the respirator programme?
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Biomonitoring. Urinary hippuric acid is a poor and non-specific marker of toluene exposure: it is derived from dietary benzoate and is also raised by sorbic acid preservatives in food, so a 'normal' result says little about solvent dose and a raised result may say nothing about work. A normal hippuric acid with 118–131 ppm in the air is exactly the discordance one expects from an unsuitable test. If biological monitoring is to be used, it should be a specific marker - urinary o-cresol at end of shift (ACGIH BEI in the order of 0.03 mg/g creatinine; verify against the current BEI list) or toluene in blood or urine - with correct sampling timing, creatinine correction and an accredited method. Meanwhile the air data already establish overexposure; biomonitoring can support but not overturn it.
Respirator programme. Half-mask respirators with organic-vapour cartridges can only be relied on if each wearer is fit-tested, medically cleared, clean-shaven at the seal, trained in donning and doffing, and given a written cartridge change-out schedule based on calculated breakthrough time. Storing cartridges in a warm cupboard and changing them 'when you can smell it' guarantees breakthrough, because odour is detected only after the cartridge has stopped working. There is also no eye protection, although toluene is irritant to eyes and mucous membranes, and no glove specification although it is dermally absorbed.
Conclusion. Neither the 'normal' laboratory result nor the issued masks provide any assurance. Both should be reported to management as inadequate controls, and masks must be described as an interim measure only.
3. Set out an action plan, distinguishing what must change immediately from what can be scheduled, and state what should happen to the pregnant worker.
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Immediate (same week). The cementing line should stop until local exhaust ventilation is installed at the glue points, or until a water-based adhesive has been substituted after reviewing the technical data sheets. In the meantime, the room needs general dilution ventilation and the work should be moved to a larger, open area. The pregnant worker must be removed from solvent exposure now and given an unexposed task at the same grade and pay - a better mask is not an acceptable answer for a fetus, because no respirator gives a protection factor that can be relied upon in a poorly ventilated room, and dermal absorption continues regardless. She should be told why, in plain language, and referred to her obstetrician.
Short term (1–3 months). Substitution is the durable solution: water-based contact adhesives or mechanical bonding eliminate the hazard. If solvent must remain, engineering controls come first - captor hoods at the glue point, enclosure, ducted exhaust - followed by administrative measures such as reducing shift length back to 8 hours and eliminating the 10-hour overtime pattern. PPE is the last line: fit-tested respirators with a documented change schedule, nitrile gloves, goggles, and training.
Surveillance and governance. Repeat personal sampling after controls, record results against the NAB, and start a symptom questionnaire and periodic health examination for the cementing group. Report the exposure situation and the corrective plan to the K3 committee, with named owners and dates. Document the advice in writing, because if the owner declines the engineering investment, the record must show what the occupational physician recommended and when.