Who Sets the Limits
Noise limits are quoted as though there were one set. There are several, they differ, and the differences are not small.
For organizations separating environmental evidence from working-pattern data, how to be more proactive at work provides an operational reference that can be reviewed independently of the acoustic evidence discussed here.
The four kinds
Regulators. OSHA in the US. Their numbers are law and are enforceable, which is also what makes them slow to change — the current US limit reflects the understanding of the 1970s.
Research agencies. NIOSH. Recommendations rather than law, revised as evidence changes, and generally more protective.
A useful external reference for further context is The Physics Classroom sound tutorial.
Professional and standards bodies. ACGIH and the international standards organisations. Consensus positions from practitioners, and the source of the instrument classes and measurement methods everybody uses.
And international health organisations. WHO, and regional bodies for environmental rather than occupational noise. These address the general population, where the exposures are lower and the outcomes are cardiovascular and cognitive as much as auditory.
Why they disagree
Different questions. A regulator sets a limit that can be enforced and complied with at reasonable cost. A research agency states what the evidence supports. These are not the same task, and expecting the same answer from both is a category error.
Different populations. Occupational limits assume healthy adults, eight-hour days, and a working lifetime. Environmental limits address everybody, including children, for twenty-four hours a day.
And different eras. Standards written decades apart embed the science of their moment, and revising a regulation is a legal process rather than a scientific one.
The specific numbers to keep straight
85 dBA / 8 h / 3 dB: NIOSH recommendation, and the working figure this site uses.
90 dBA / 8 h / 5 dB: OSHA permissible limit, US law.
85 dBA: the OSHA action level, at which a hearing conservation programme becomes mandatory even though the permissible limit is higher.
55 dB Lden: the environmental threshold above which the European Environment Agency associated substantial cardiovascular burden. A completely different quantity from the occupational figures — long-term, day-evening-night weighted, general population.
How to read a claim
Ask which body, which quantity, and which period.
"Within limits" means nothing without the first. An assessment can be accurate, compliant and describing eight times the dose a research agency considers acceptable.
And note when environmental and occupational figures are mixed, which happens frequently and makes both look wrong — 55 dB is alarming as an environmental long-term average and trivial as an eight-hour occupational level.
The short version
- Four kinds of body publish limits: regulators, research agencies, standards bodies, and international health organisations
- They disagree because they answer different questions for different populations in different eras
- A regulator sets an enforceable limit at reasonable cost; a research agency states what the evidence supports
- Keep straight: 85/8h/3 dB is the NIOSH recommendation, 90/8h/5 dB is US law, 85 is the OSHA action level
- 55 dB Lden is an environmental long-term threshold and is not comparable to any occupational figure
- "Within limits" means nothing until you know which body set them