Case study: an aluminium machining plant at 98.8 dB(A)

The site

An aluminium-profile machining and fabrication plant in Gloucestershire, running a bank of CNC machining and processing centres (profile cutting, routing and sawing) alongside a warehouse, a packing area and offices on a mezzanine. We measured fourteen task and area positions to Class 1 standard (BS EN ISO 9612) across a normal production day and calculated each area's daily personal exposure, L_EP,d.

What we found

Five machining centres sat at or above the 85 dB(A) upper action value — the worst at 98.8 dB(A), with four more between 88.6 and 95.1 dB(A). The general production floor, forklift routes, walkways and packing fell in the 80–85 dB(A) band, and the offices were quiet at 58–62 dB(A). No peak came near the 135 dB(C) action value (the highest was 112.1 dB(C)) — so the risk here is sustained level, not sudden impact.

The insight that pays for the survey

At 98.8 dB(A) an unprotected operator on the worst machining centre reaches a full day's permissible noise dose in about 20 minutes — against a whole 8-hour shift at the 85 dB(A) limit. With five centres over the upper action value, this isn't a single machine to screen off; it's a whole machining department that needs mandatory Hearing Protection Zones, the right protectors and health surveillance for every operator while engineering controls are worked through machine by machine. Because the peaks are low, the entire risk is cumulative dose — exactly what a ‘that machine sounds fine for a minute’ judgement misses.

What the client got

• Mandatory Hearing Protection Zones around the five machining centres, with signage and boundaries that match where the 85 dB(A) line actually falls.
• A protector spec matched by area — higher attenuation at the machines, lighter protection for the 80–85 dB(A) floor — so people are protected without being cut off from warnings.
• Audiometry for the machining operators, and a prioritised engineering-control review (enclosure, damping, guarding) so the noise itself comes down over time, not just the dose at the ear.
• Lower-noise office and warehouse workstations kept segregated from the machining line.

That is the difference between a survey that just says “you're over the limit” and one that tells you exactly where to act — and keeps it current, which is what the 4-Year Care Plan is for.