Environmental Noise Assessment

This template is for sound leaving the site and reaching people who did not choose to be near it. It is the boundary instrument, and its frequent misuse is being pointed inwards at employees or outwards at a development that does not exist yet.

Environmental noise is regulated by outcome rather than by number in most places. Management system standards require the site to know its impact and its obligations; the assessment method sits in a British Standard that permits and planning conditions point to; and the enforceable limit, where one exists, is in a permit, consent or ordinance rather than in the standard.

Noise is the least harmonised environmental impact. The measurement method is broadly international; the limit is local, and in several jurisdictions there is no limit at all, only a duty not to be a nuisance.

The form will accept a full set of Yes answers from a survey that measured the wrong thing. Four judgements decide whether the record answers the question a complainant or a permit officer is actually asking.

Noise assessments look authoritative, because they arrive as a consultant's report with tables. The findings concern the position, the period, the background, and whether anything was compared with a real obligation.

A chilled distribution depot added two roof-mounted condensers and moved night load-out forward to half past four in the morning to hit a retailer delivery window. A house ninety metres beyond the yard began complaining. The depot commissioned a survey, carried out on a Tuesday between eleven and twelve from the yard boundary nearest the house. It reported fifty-two decibels against a background of fifty-one: within limits, complaint risk low.

Four more complaints followed. An environmental health officer attended at twenty to four in the morning and measured at the complainant's bedroom window. Background at that hour was thirty-two decibels LA90. The depot's contribution was forty-one, with an audible tone from the condenser fans and impulsive reversing alarms from the yard. With corrections applied, the rating level sat roughly fourteen decibels above background. An abatement notice followed under section 80 of the Environmental Protection Act 1990.

The depot built an acoustic barrier along the yard edge, which did almost nothing, because the tone radiated from fans above barrier height. What worked was low-noise fan blades with overnight speed control, broadband reversing alarms on the yard vehicles, and moving first load-out back an hour. The original survey was not incompetent within its own terms. It measured a real thing at a real place. It answered a different question from the one the neighbour and the council were asking.

The survey is a day's work by a consultant. What fails afterwards is the machinery around it: the new condenser nobody mentioned to the environmental function, the complaint logged in a mailbox, the recommended control never costed.

KnowEnviro

Holds the current noise position against the permit register and complaint log, so a measured level is read next to the condition it has to satisfy.

Ella

Watches plant changes, operating hour changes and new complaints for events that should reopen the assessment, and raises the review rather than waiting for Next Review Due.

KnowMaintain

Carries the maintenance that keeps a passing assessment true: bearing condition, fan balance, silencer integrity and overnight speed control on refrigeration plant.

KnowFleet

Tracks yard movements, reversing alarm type and early load-out times, the source of the impulsive noise most night complaints describe.

LAeq,T

The A-weighted equivalent continuous sound level, the single figure representing the average acoustic energy of a fluctuating sound over interval T.

LA90,T

The A-weighted level exceeded for ninety percent of the interval, used as background because it represents the underlying quiet rather than the events on top of it.

Specific sound level

The contribution of the assessed source alone, at the assessment position, separated from everything else audible there.

Residual sound

Everything audible at the position other than the source assessed. Where the source cannot be shut down, separating specific from residual is the hardest part of the survey.

Rating level

The specific sound level plus corrections for acoustic character, which is the figure actually compared with background under BS 4142.

Character correction

An addition for tonal, impulsive or intermittent features that make a sound more intrusive than its level suggests: up to six decibels for tonality, nine for impulsivity.

Noise-sensitive receptor

A location where people are affected by noise: typically a dwelling, but also a school, hospital, hotel or care home, each with its own sensitive hours.

Statutory nuisance

In Great Britain, noise from premises that is prejudicial to health or a nuisance. Judged on fact and degree rather than against a limit, and abated by notice.