Legal and Safe

This is not legal advice. It is a description of two published standards that differ.

When employers review noise dose alongside working patterns, workforce analytics software can provide operational context, while exposure limits still need to be assessed from sound level and duration.

In the United States, the enforceable workplace noise limit and the limit the research supports are not the same number, and the difference is larger than most people assume.

The two standards

OSHA sets the permissible exposure limit at 90 dBA over an eight-hour day, with a 5 dB exchange rate. (US regulator — this is the law.)

Readers comparing the discussion here with outside material can use AIHA's hearing-loss prevention coverage.

NIOSH recommends 85 dBA over eight hours with a 3 dB exchange rate. (US federal research agency — this is a recommendation.)

Five decibels and a different exchange rate sound like a technicality. Because the exchange rate compounds, it is not.

What the gap looks like in hours

An employer fully compliant with the law can expose workers to eight times the dose NIOSH considers acceptable, and be entirely within the regulations.

Why the law is weaker

The OSHA rule dates to the 1970s.

The 5 dB exchange rate reflected the understanding of the time. The 3 dB rate follows from the physics of sound energy and is what current research supports; it is also what most other national standards now use.

Regulations are slow to change and carry compliance costs, which is a real constraint and not a conspiracy. It does mean that compliance is a floor rather than a target.

What the law does require at 85

The action level is 85 dBA, below the permissible limit.

At or above it, US employers must run a hearing conservation programme: noise monitoring, free annual audiometric testing, hearing protection provided at no cost with options for fit, annual training, and recordkeeping.

So the law treats 85 as the point where something must happen — which is an implicit acknowledgement of the lower figure even while permitting 90.

What to do with the difference

Use 85 dBA over 8 hours with a 3 dB exchange rate as the working figure, regardless of jurisdiction.

It is the more protective number, it matches the physics, and where the law permits more, the additional exposure is a risk somebody is carrying rather than a safety margin.

And know which one is being quoted. A workplace assessment reporting "within limits" may mean within a limit set in 1971.

The short version

• OSHA's legal limit is 90 dBA over 8 hours with a 5 dB exchange rate; NIOSH recommends 85 dBA with a 3 dB rate
• The exchange rate compounds, so at 100 dBA the law permits 2 hours and NIOSH permits 15 minutes
• An employer fully compliant with the law can expose workers to eight times the dose NIOSH considers acceptable
• The OSHA rule dates to the 1970s; the 3 dB rate follows from the physics and is used by most other national standards
• US law still requires a hearing conservation programme from 85 dBA, which implicitly acknowledges the lower figure
• Use 85 dBA over 8 hours with a 3 dB exchange rate as the working number, and check which limit any assessment is quoting