Measurements · Noise
Peak Level (Lpeak)
Also known as peak noise level
Peak sound pressure level (C-weighted peak used for impulse-noise limits).
What it is
What is Lpeak (peak sound level)?
Lpeak is the true instantaneous maximum sound pressure reached during a measurement, expressed in decibels. Unlike Lmax, it is measured with no time weighting at all, so it captures the fastest transients (the sharp crack of an impact, a hammer blow, a nail gun, a drop forge, or gunfire) that slower metrics smooth away. Because those impulsive events are rich in low- and mid-frequency energy, Lpeak is normally C-weighted (written LCpeak) rather than A-weighted, since C-weighting reflects the ear's response at the high sound pressures involved. It is always the highest of the noise metrics, sitting above both Lmax and Leq.
Peak level answers a different question from the average and the maximum: not how loud on the whole, but how violent the single sharpest pressure spike was.
Band resolution: reported broadband plus 1/1 octave and 1/3 octave. The metric and its frequency band are independent. Check the sound-capable devices below for what each one reports.
Health and operational effects
A single sufficiently loud impulse can cause immediate and permanent hearing damage (acoustic trauma) by mechanically injuring the inner ear, without the years of accumulated exposure that gradual noise-induced hearing loss requires. This is why occupational noise regulations set a separate peak criterion, expressed as an LCpeak, alongside the daily exposure limits. The peak criterion guards against instantaneous injury; the average criterion guards against cumulative damage. Impulsive, high-peak noise is characteristic of forging, stamping, cartridge-operated tools, ballistics, and heavy impacts.
For employers with impulsive noise sources, Lpeak is therefore a distinct compliance number that cannot be inferred from the average level, and hearing protection must be adequate for the peaks as well as the dose.
Limits
Peak Level (Lpeak) Limit Values
The published values, by averaging period; each links to the standard that sets it.
Impulse peak (OSHA ceiling)
Lpeak is reported in decibels, normally dB(C) for peak, and is compared directly against the peak exposure action and limit values rather than against averaged criteria; the applicable figures appear in the limit table on this page. Interpret it as an instantaneous ceiling: a single exceedance is significant because a single impulse can injure hearing, so unlike an average it does not need to be sustained to matter. Read Lpeak together with Leq, since a workplace can be within its average limit yet exceed the peak limit, or the reverse.
How it is measured
How Peak Level (Lpeak) Is Measured
Lpeak is captured by a sound level meter or noise dosimeter built to the IEC 61672 standard, which must have true peak detection able to catch a transient lasting well under a millisecond; an ordinary averaged reading would miss it entirely. C-weighting is normally applied. Because this is a precision measurement beyond the built-in ambient sound metrics, Lpeak is measured with an external IEC 61672 instrument logged on a Thiamis gateway, reported alongside the anchor metric Leq so that both peak and cumulative exposure are recorded together.
An instrument on Thiamis2
A third-party instrument connected to a Thiamis gateway, reporting into the same Environet account.
Placing noise monitors
For personal exposure the peak is measured by a dosimeter worn near the worker's ear, close to where the impulsive tool or process is operated, since peak pressure falls off rapidly with distance. For area assessment the microphone is placed near the impulsive source, clear of reflecting surfaces, and fitted with a windshield outdoors. Because impulsive events are short and unpredictable, continuous logging is needed to be certain the true peak has been captured rather than a lower value from between events.
Every device and option that measures Peak Level (Lpeak) 2
| Device / option | Type | Base platform | Measures |
|---|---|---|---|
 Cirrus Research · 151B, 152B, 151A… | Noise Monitors | Thiamis | |
 TSI · SP-SE-1, SP-SE-1-1/1, SP-SE-1-1/3… | Noise Monitors | Thiamis |
Where it is monitored
Solutions That Monitor Peak Level (Lpeak)
Each one links to the solution page showing what that industry measures it for.
Noise Monitoring
Often addedEnvironmental and occupational sound levels
Occupational Safety & Industrial Hygiene
Often addedWorker exposure, confined space, and heat stress
Related
More in Noise
Questions
Peak Level (Lpeak) FAQ
What is the difference between Lpeak and Lmax?
Lpeak is the true instantaneous peak sound pressure measured with no time weighting, while Lmax is the highest level under a Fast or Slow time weighting. Lpeak is always higher and is used specifically for impulsive noise and immediate hearing-damage risk, while Lmax characterizes the loudest sustained moment. They are separate metrics and are not interchangeable.
Why is Lpeak usually C-weighted?
Because impulsive events carry strong low- and mid-frequency energy and occur at high sound pressures, where the ear's response is better represented by C-weighting than by the A-weighting used for average exposure. Occupational peak limits are consequently written as LCpeak values.
Can a single loud bang damage hearing?
Yes. A sufficiently high peak pressure can cause immediate, permanent acoustic trauma from one event, which is why regulations set a peak limit distinct from the daily average. This is the reason hearing protection must be selected for the peaks present, not just the average level.
How do I monitor peak noise?
Peak measurement needs an external IEC 61672 sound level meter or dosimeter with true peak detection on a Thiamis gateway, logging LCpeak alongside Leq. Use the configurator to combine noise with the other parameters your assessment requires.
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