Silica and Noise Exposure in a Tunnel Heading
At a tunnel enlargement project, 10 workers operate a hydraulic breaker and a ventilation fan in a 6 m diameter heading. Personal noise dosimetry over a 12-hour shift gives an 8-hour equivalent of 94 dB(A) for the breaker operator and 88 dB(A) for the labourers. Respirable dust sampling shows 0.15 mg/m³ respirable crystalline silica, compared with the project's adopted occupational exposure limit of 0.025 mg/m³; the sample was taken over 6 hours. Two labourers report breathlessness on climbing 30 steps, and one reports ringing in the ears that persists after the shift. Hearing protection is issued as foam plugs with a claimed SNR of 35 dB, but fit checks are not done and workers wear them under ear defenders only when the breaker runs. Health surveillance consists of a pre-employment questionnaire. The project manager says dust is 'unavoidable in tunnelling' and asks you to sign off the exposure as acceptable.
1. Assess the exposure and state whether the project can be signed off as acceptable. What legal duties apply?
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Assessment: the breaker operator's 94 dB(A) 8-hour equivalent exceeds the 85 dB(A) action level and the 90 dB(A) limit; the labourers at 88 dB(A) also exceed the action level. The silica result of 0.15 mg/m³ is six times the adopted 0.025 mg/m³ limit, and because sampling covered only 6 of a 12-hour shift, the full-shift exposure is likely to be higher. The two symptomatic workers and the persistent tinnitus are health effects consistent with the exposures, not unrelated complaints.
Conclusion: the exposure cannot be signed off as acceptable. The project manager's statement that dust is unavoidable is not a control measure; tunnelling dust can be suppressed, extracted and monitored.
Legal duties: assess and control risks to health; apply the hierarchy of control; provide health surveillance where there is a risk of occupational disease; inform, train and supervise workers; provide suitable PPE as a last resort and ensure it is used and maintained; keep exposure and health records; report occupational disease where required. Signing off would misrepresent the exposure and could expose the signatory and the employer to enforcement action.
2. Recommend controls in priority order and explain the expected effect on exposure.
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1. Eliminate or reduce the source. Use a larger breaker with lower vibration and noise, or break rock by mechanical ripping rather than prolonged hydraulic breaking where geology allows. Sequence work so the breaker runs when fewer workers are in the heading.
2. Engineering controls. Apply water spray or mist at the breaker point and on the muck pile; use on-tool extraction or a local exhaust ventilation hood close to the dust source; maintain and extend the forcing ventilation so clean air reaches the breathing zone; fit acoustic enclosures or silencers to the breaker and fan; line chutes and reduce drop heights.
3. Administrative controls. Rotate workers out of the breaker zone; shorten exposure by task rotation; establish a clean rest area and a dirty-to-clean changing procedure; prohibit dry sweeping; provide washing facilities before eating.
4. PPE. Fit-test FFP3 respirators for the silica exposure, with face-fit checks and a clean-shaven policy where relevant. Provide hearing protection selected for the actual noise level, with fitting checks; do not rely on the SNR rating alone because real-world attenuation is lower. Ear defenders over plugs may be needed for the breaker operator, but only if communication and heat stress allow.
Reasoning: engineering controls reduce the dust and noise at source and protect everyone in the heading; PPE protects only the wearer and depends on fit and consistent use. Current practice fails because PPE is worn intermittently and fit is not checked.
3. Design health surveillance and training, including what to do with the two symptomatic workers.
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Health surveillance: baseline and annual audiometry for all exposed workers, with a questionnaire for tinnitus and hearing difficulty; spirometry and a respiratory questionnaire for silica exposure;记录 of results and referral for any worker with abnormal findings. The two breathless labourers should be referred for medical assessment promptly, and the worker with persistent tinnitus should have audiometry and be assessed for noise-induced hearing loss. Do not simply move them without medical advice; consider temporary removal from the highest exposure while the assessment is completed.
Training: cover the health effects of silica and noise, where exposure occurs, how controls work, how to fit and check PPE, the importance of not dry sweeping, reporting symptoms early, and the results of monitoring. Use the workers' languages and include agency workers. Record attendance and understanding, not just signatures.
Records: keep exposure monitoring, fit-test records, health surveillance outcomes and referrals confidential but available to the occupational health professional. Review the risk assessment when health surveillance reveals a problem.
Reasoning: health surveillance is not a substitute for control; it detects harm early and tests whether controls are working. Training must change behaviour, so it should be practical and checked, not a one-off briefing.