A Hearing Protection Zone (HPZ) is an area that has to be sign-posted and where hearing protection becomes compulsory, once noise reaches the upper exposure action value. For the full legal detail on what that means and what it requires, see Hearing Protection Zones explained. This page focuses on a narrower, practical question: once you know where an HPZ needs to be, how do you actually show it — on a plan, on site, and to people who need to understand it fast?
What triggers a Hearing Protection Zone
Why a written boundary is hard to communicate
A standard assessment states an HPZ in words and figures — "the area within roughly 4m of Press 3" — or marks it on a static, hand-annotated plan. Both work, but neither makes the boundary easy to picture for someone who wasn't there for the measurement: where exactly does it start relative to the walkway, does it change shape around a partition, does a second source's zone overlap it. Those are exactly the questions a site team, a signage contractor, or an inspecting insurer will actually ask.
How the boundary is visualised on a 3D map
Because a 3D noise map is built from real measured contours rather than an estimate, the 85 dB(A) / 137 dB(C) threshold can be traced directly onto the map at the actual scale and shape of the room — not approximated as a circle around a machine. Two views, drawn from the same underlying data:
- 2D plan view — the HPZ boundary rendered as a dB contour line clipped to the real shape of the floor, ready to print or hand to a signage contractor.
- 3D landscape / room model — the same boundary shown spatially against the actual layout, useful for briefing a board, an insurer, or anyone who has never read a noise report before.
Practical uses
Where the sign actually goes
A scale boundary tells a signage contractor exactly where the line is, rather than "somewhere near the press."
Briefing the team
A picture communicates faster than a paragraph — useful for site inductions and refresher talks.
Evidence of control
A clear visual record of where zones sit and how they were derived, alongside the written assessment.
Did the control work?
Re-map after remedial work (a screen, a quieter machine, a layout change) and see the zone shrink — evidence the change actually worked.
See a real worked example
The press shop example shows a real HPZ boundary marked on both the 2D plan and the 3D landscape from an actual survey, if you want to see this in context before asking about your own site.
Pricing
HPZ boundaries are included as standard on every 3D noise map, from £750 + VAT. See the full 3D noise mapping overview for the tier breakdown, or request a quote directly.
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