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Earplugs or an enclosure

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Earplugs or an enclosure

At a plastics extrusion plant, a noise survey reports 93-96 dB(A) at the granulator, where six operators work a 12-hour shift, four days on. The production manager proposes issuing foam earplugs from a dispenser at the door, putting up a 'Hearing Protection Zone' sign and instructing supervisors to enforce use. The PPE cost is about GBP 400 a year. An acoustic enclosure for the granulator has been quoted at GBP 14,000 with a six-week lead time. One operator removes his plugs mid-shift because he says he cannot hear the forklift reversing alarm or his colleague calling him. Audiometry last month showed a 15 dB notch at 4 kHz in one operator's left ear; he has run the granulator for nine years.

1. Judge the production manager's proposal. What is acceptable in it, what is not, and why?

Read the worked answer

It is half a control presented as a whole one.

Acceptable: hearing protection and a marked hearing protection zone are legally required at this level of noise, so they are not optional extras to be traded against the enclosure. Providing protection, training, supervision and health surveillance is a baseline duty.

Not acceptable: treating it as the answer. PPE sits at the bottom of the hierarchy for reasons that are visible in this scenario:

  • It protects only the wearer, only while it is in and fitted, and it fails silently. Nothing on the shop floor tells you it has stopped working.
  • The operator taking his plugs out to hear the forklift alarm is the decisive detail. The control is creating a new risk (loss of alarm audibility and communication), which means it is not a suitable control for this task, however well it attenuates.
  • The cost argument is weak. Over the life of the plant, GBP 14,000 against six operators' hearing, a compensation claim and an enforcement visit is not disproportionate, and 'reasonably practicable' is not satisfied by comparing it to a GBP 400 dispenser.
  • A 4 kHz notch in a nine-year operator is an early indicator, not a footnote. It means exposure has already had an effect and the clock is running.

So: keep the plugs, fix the selection (level-dependent or electronic protection that lets alarms through), and commission the enclosure as the actual solution with a date attached to it.

2. What should be done during the six weeks before the enclosure arrives, and what must be verified rather than assumed?

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The interim period is six weeks of known overexposure, so it needs its own plan, written down as temporary with an end date tied to the enclosure installation.

  • Selection and fit: move away from plain foam plugs to level-dependent electronic earmuffs, or at minimum a protect-or that still allows the reversing alarm to be heard; fit-test them and train on insertion. Over-protection is a real failure mode here, not a theoretical one.
  • Reduce time at the source: rotate operators off the granulator, move non-essential tasks away, and consider whether the 12-hour shift is part of the problem.
  • Alarms: check the forklift alarm is audible with protection on, and add a visual warning (flashing beacon) so audibility is not the only channel.
  • Machine condition: loose panels, worn bearings and missing guards all raise noise; a maintenance pass may buy several dB cheaply.
  • Health surveillance: follow up the operator with the notch, refer as required, and keep audiometry for the rest of the group.

Verify, do not assume: ask the enclosure supplier for predicted dB at the operator position and a performance figure they will stand behind, and confirm the survey was taken where people actually stand rather than somewhere convenient. Record who owns each interim action and the date the temporary measures are withdrawn.

3. Once the enclosure is installed, how will you decide whether the residual risk is acceptable, and what would you do if it is not?

Read the worked answer

You decide with a measurement, not with a completion certificate.

  1. Re-survey at the operator position with the enclosure running under normal production conditions (not in a quiet workshop with the machine idling). Compare against the exposure action values, weighted for the 12-hour shift rather than an 8-hour assumption.
  2. Check what the number does not capture: tonality, peak noise, and whether operators can hear alarms and each other. Ask them; their answer is data.
  3. Keep protection as a residual measure if levels remain in the action value range, and keep hearing protection zones signed.
  4. Continue audiometry and compare trends for the six operators, treating any further threshold shift as evidence the control is not holding.
  5. Watch behaviour as a leading indicator: if people are still taking protection off, the control is still failing, whatever the meter says.

If the result is still too high, go back up the hierarchy rather than back to the dispenser: further enclosure or segregation, remote operation or automation of the granulator, administrative reduction of exposure time, and a revised action plan with dates. Record the decision and its basis, because the reasoning is what an inspector will ask about if the audiometry ever appears in a compensation claim.