Occupational Noise Exposure Standard: The 85 dB(A) Limit Explained for Employers

Australia’s occupational noise exposure standard establishes two limits: a time-weighted average (LAeq,8h) of 85 dB(A) and a peak/impulse limit (LC,peak) of 140 dB(C). These are not arbitrary numbers—they’re science-based thresholds designed to protect workers from noise-induced hearing loss. Yet many Australian employers misunderstand them, leading to inadequate controls and preventable hearing loss. This guide explains the standard in practical terms.

The Standard Explained

Two Concurrent Limits

Australian occupational noise law (WHS Regulation 57, based on Safe Work Australia guidance) specifies two simultaneous limits:

1. LAeq,8h = 85 dB(A)

LAeq,8h: A-weighted equivalent continuous sound level over 8 hours
85 dB(A): The decibel level (A-weighted, accounting for human ear sensitivity)
8-hour exposure: The reference period (an 8-hour workday)
Interpretation: If a worker is exposed to noise levels that average 85 dB(A) LAeq over 8 hours, they’ve reached the exposure standard

2. LC,peak = 140 dB(C)

LC,peak: C-weighted peak sound pressure level (accounts for very high-frequency sounds)
140 dB(C): The decibel level (C-weighted)
Peak/Impulse: The instantaneous maximum sound pressure, not averaged
Interpretation: A single instantaneous noise event (gunshot, explosion, impact) cannot exceed 140 dB(C) regardless of duration

Both Limits Apply Simultaneously

A workplace must comply with BOTH limits:

If LAeq,8h is below 85 dB(A) but a single impulse exceeds 140 dB(C), the workplace is non-compliant
If LAeq,8h is 85 dB(A) but peak noise never exceeds 140 dB(C), compliance depends on the time-weighted average

Both limits must be met for full compliance.

What LAeq,8h Means

A-Weighting Explained

A-weighting (dB(A)) mimics the human ear’s frequency response. The ear is less sensitive to very low and very high frequencies. A-weighting emphasizes the frequencies most important for speech and hearing damage (roughly 500–4000 Hz):

Low frequencies (<250 Hz): De-emphasised (less damaging perceptually)
Mid frequencies (500–4000 Hz): Emphasis (most damaging, most important for speech)
High frequencies (>4000 Hz): De-emphasised relative to mid-frequencies

Result: dB(A) measurements correlate better with hearing damage risk than unweighted dB measurements.

Equivalent Continuous Level

“Equivalent continuous” means the standard compares actual, fluctuating noise to an equivalent steady sound level:

Example:

Worker experience: 70 dB(A) for 4 hours, then 90 dB(A) for 4 hours
LAeq,8h calculation: The equivalent continuous level that represents this exposure is approximately 82 dB(A)
Compliance: 82 dB(A) LAeq,8h is below 85 dB(A), so compliant

The standard accounts for both level and duration—noise fluctuations are averaged over the day.

8-Hour Reference Period

The standard assumes an 8-hour workday. For shift workers on different schedules, the time-weighted average is still calculated over their actual work period and converted to an 8-hour equivalent.

The Doubling Rule / Trading Ratio

One of the most important concepts for understanding the 85 dB(A) standard is the doubling rule or trading ratio:

For every 3 dB(A) increase in noise level, the allowable exposure time is halved.

This reflects the physics of sound energy:

85 dB(A): 8 hours exposure allowed
88 dB(A): 4 hours exposure allowed (3 dB increase = half time)
91 dB(A): 2 hours exposure allowed
94 dB(A): 1 hour exposure allowed
97 dB(A): 30 minutes exposure allowed
100 dB(A): 15 minutes exposure allowed

Implication: A worker exposed to 88 dB(A) for a full 8-hour shift is exceeding the standard (equivalent to 85 dB(A) for only 4 hours). Control measures must be implemented to reduce either the noise level or exposure duration.

The 140 dB(C) Peak Limit

The peak limit (140 dB(C)) is independent of time. A single instantaneous noise event exceeding 140 dB(C) is non-compliant, regardless of how brief:

Examples of impulses that might approach or exceed 140 dB(C):

Gunshot (155+ dB(C))
Explosion (150+ dB(C))
Pneumatic nail gun (140+ dB(C) at close range)
Drop forge hammer impact (140+ dB(C))
Large industrial press (140+ dB(C))

Workplaces with impulse hazards must implement controls to keep peak noise below 140 dB(C).

Industries Where the Standard Is Regularly Exceeded

Most workplaces are below 85 dB(A) LAeq,8h, but several industries frequently exceed it:

Mining (underground and surface): Drilling, blasting, heavy machinery
Construction: Pneumatic tools, jackhammers, circular saws, heavy equipment
Metal fabrication and foundries: Grinding, forging, cutting, heat treatment
Transport maintenance: Impact wrenches, grinders, engine testing
Defence and military: Weapons testing, explosives, aircraft
Entertainment (live music venues): Amplified music, speakers
Woodworking: Table saws, routers, sanders (if high production volume)

For these industries, the 85 dB(A) standard almost certainly applies, triggering hearing protection and audiometric testing obligations.

How to Measure if Your Workplace Exceeds the Standard

Sound Level Meter Survey

A simple preliminary assessment uses a sound level meter:

Measure sound level in dB(A) at worker locations
If any measurement is ≥85 dB(A), the standard may be exceeded
Limitation: This is a snapshot, not a time-integrated measurement. You’re not calculating LAeq,8h

Dosimetry Survey

A worker wears a personal noise dosimeter throughout their shift:

The dosimeter measures the worker’s actual noise exposure over time
Calculates LAeq,8h automatically
Most accurate method for determining compliance
Cost: $500–$2,000 for professional dosimetry assessment

The 15-Minute Rule (Quick Assessment)

A rough rule of thumb: If you must raise your voice to speak normally at 1 metre distance, noise likely exceeds 85 dB(A). This is NOT a precise measure but indicates need for professional assessment.

Implications of Exceeding the Standard

If your workplace exceeds the 85 dB(A) LAeq,8h standard:

Control measures required: Implement engineering, administrative, and/or HPE controls
Hearing protection mandate: Workers must be provided with and required to use hearing protection
Audiometric testing mandate: WHS Reg 58 requires testing for regularly exposed workers
Information and training: Workers must be informed about noise risk and HPE use
Regulator notification potential: Your workers’ comp insurer may notify WHS regulators if claims occur; regulator may audit your controls

Frequently Asked Questions

Q1: If we stay under 85 dB(A), do we need audiometric testing?

No. Audiometric testing is required only if workers are regularly exposed at or above 85 dB(A) LAeq,8h and are required to use hearing protection.

Q2: Does a short exposure to 90 dB(A) exceed the standard if the daily average is 82 dB(A)?

No. The standard uses a time-weighted average. Short high-level exposures are allowed if daily average stays below 85 dB(A).

Q3: What if noise is only 84 dB(A)—do we need controls?

84 dB(A) is below the standard, so formal controls aren’t legally mandated. However, best practice is to address any occupational noise exposure, even if below the standard.

Q4: How accurate is a sound level meter?

Professional sound level meters are accurate to ±1–2 dB if used correctly. Consumer sound level meter apps are much less reliable (±5–10 dB errors).

Q5: Can we use hearing protection to comply, without engineering controls?

Hearing protection can bring the effective exposure below 85 dB(A), but engineering controls are preferred (hierarchy of controls). HPE should be the last resort.

Q6: Does the 3 dB doubling rule apply above 85 dB(A)?

Yes. The 3 dB trading ratio applies throughout the range. It’s based on acoustics physics, not just at the standard threshold.

Q7: If peak noise exceeds 140 dB(C) even once, are we non-compliant?

Yes. The peak limit is absolute. A single event exceeding 140 dB(C) means controls are inadequate.

Q8: Can we average peak noise over time (like LAeq)?

No. The 140 dB(C) peak limit is instantaneous—a single maximum. Peak noise can’t be “averaged down.”