Understanding EPA NG4 noise limits for your licensed site
A plain-English guide to the EPA's NG4 guidance on noise from industrial activity — what the daytime and night-time limits mean, and how to demonstrate compliance.
Dr. Aoife Ryan Principal Environmental ScientistIf your facility operates under an EPA licence, noise is almost certainly one of the conditions you’re expected to manage. The reference point in Ireland is the EPA’s Guidance Note for Noise: Licence Applications, Surveys and Assessments (NG4) — and understanding it is the difference between a survey that reassures your regulator and one that raises questions.
What NG4 actually asks for
NG4 sets out how noise from a licensed activity should be measured, assessed and reported. In practice, it usually comes down to three things:
- Boundary noise limits, typically expressed as
LAr,Tvalues for daytime, evening and night-time periods. - An assessment of tonal or impulsive character — a steady hum or a repetitive bang is more noticeable, and more likely to generate complaints, than broadband noise at the same level.
- A comparison against the prevailing background, so the contribution of your site is understood, not just the total measured level.
Typical limit values
While your specific licence conditions always take precedence, many EPA licences reference limits in the region of:
| Period | Typical limit (LAr,T) |
|---|---|
| Daytime (07:00–19:00) | 55 dB |
| Evening (19:00–23:00) | 50 dB |
| Night (23:00–07:00) | 45 dB |
Always check the exact values in your licence. Limits vary with location, the sensitivity of nearby receptors and the history of the site.
Where sites commonly slip up
- Measuring on the wrong day. A survey taken when a key noise source is offline doesn’t represent normal operation — and won’t stand up to scrutiny.
- Ignoring weather. Wind direction and speed materially affect readings. NG4-compliant surveys record meteorological conditions alongside the data.
- Missing tonal penalties. A level that’s technically “under limit” can still fail once a tonal penalty is added.
How we approach it
Our noise surveys are scoped to your specific licence, carried out with calibrated Class 1 instrumentation, and reported with the character assessment and background comparison NG4 expects. The result is a document you can hand to the EPA with confidence.
If you’re preparing for a licence review or responding to a noise complaint, get in touch and we’ll recommend the right survey scope.
About the author
Dr. Aoife RyanPrincipal Environmental Scientist
Aoife leads our noise and air quality practice. With a doctorate in environmental acoustics and over a decade advising Irish industry, she specialises in EPA licence compliance and complaint resolution.
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