Hazardous substances consultation zones explained

A chemical works, a gas holder, a fuel depot or a high pressure pipeline puts a consultation zone around itself, and any planning application inside that zone is referred to the Health and Safety Executive. The regulator then advises the council either that it does not advise against the development, or that it does. An advise-against response is not a veto, and in practice very few schemes are approved over one.

The zones are invisible on the ground and they are not drawn on most constraint plans, so sites get bought inside them by people who had no idea.

What creates a consultation zone

Two things. The first is a site holding a hazardous substance above a controlled quantity, which needs hazardous substances consent under the Planning (Hazardous Substances) Act 1990 and the 2015 Regulations, and which may also be regulated under the Control of Major Accident Hazards Regulations 2015. The second is a major accident hazard pipeline, typically high pressure natural gas or a fuel line.

For each, the Health and Safety Executive sets a consultation distance based on the substance, the quantity and the containment. Within that distance the local planning authority is required to consult the Executive on applications, under the consultation arrangements in the Development Management Procedure Order 2015.

The distance is usually split into inner, middle and outer zones. Risk falls with distance, so the same proposal can attract an advise-against in the inner zone and no objection in the outer one.

These are not amenity zones. They exist because of individual and societal risk of death from a major accident, which is why the advice is binary rather than a matter of mitigation and condition.

Finding the zones that affect a site

There is no single public map you can open and read. The zones sit in the Executive's land use planning system, which local planning authorities and consultants access to obtain advice for a specific proposal at a specific location.

Three practical routes. Ask the local planning authority whether the site falls within a consultation distance, which the case officer can check in minutes. Ask the Executive directly through its planning advice route before submitting. And look at the surroundings: a site within a few hundred metres of a gasholder, a tank farm, an industrial estate with a chemical works or a marked pipeline route deserves the question before anything else.

For pipelines, the operator is the other source. Pipeline routes are recorded on land registry titles and in local searches, and operators publish contact routes for enquiries about proximity to their assets.

Do this at the option stage. A residential appraisal that has assumed 90 units on a site where the inner zone crosses the eastern third is not an appraisal at all.

How the safety regulator gives its advice

The methodology assesses the risk to the people who would occupy the proposed development, using the type of development, its size and the vulnerability of its occupants, set against the risk contours around the installation.

The output is one of two answers. Do not advise against, meaning the Executive raises no objection. Or advise against, meaning it considers the risk to the proposed population unacceptable.

For larger developments a societal risk assessment is applied as well, which looks at the chance of an incident affecting many people at once rather than the risk to an individual. This is why a scheme of 300 homes can attract different advice from a scheme of 30 in the same location.

The advice concerns safety only. The Executive does not consider housing need, viability or design, and arguing those points in response to its advice misses the audience.

Sensitivity levels and the development types in each

Development is sorted into sensitivity levels, broadly as follows.

The higher the level, the wider the area within which development is advised against. A warehouse and a primary school on the same plot get very different answers.

Occupancy density does work inside a level too. Ten flats and 200 flats are both housing, and the societal risk element separates them.

Where a mixed use scheme is proposed, the whole of it is assessed, so an otherwise acceptable commercial scheme with a nursery on the ground floor can attract an objection because of the nursery.

Pipelines and their easements

Pipelines carry two separate constraints that people routinely confuse.

The easement is a private property right, usually a strip either side of the pipeline within which the operator controls what can be built, planted or excavated. That is a matter of title and negotiation with the operator, not planning.

The consultation zone is wider, statutory and about risk. A proposal can sit well clear of the easement and still be inside the zone. Both have to be dealt with, and the operator's consent to work near the line is a separate exercise with its own lead time.

Construction near a pipeline also brings method constraints: no heavy plant crossings outside agreed points, restrictions on excavation depth, and supervision requirements. Build those into the construction management plan rather than discovering them during mobilisation.

What happens when the advice is against

The application does not stop. The authority weighs the advice as a material consideration, and where it is minded to grant permission against that advice it must notify the Executive and allow a period for the matter to be considered, during which the Secretary of State can call the application in.

Councils very rarely approve over an advise-against, for reasons that are easy to understand. A committee that overrides safety advice owns the consequences.

So treat an advise-against as a design problem rather than an argument to be won. The realistic responses are to move the sensitive parts of the scheme, to reduce the population within the higher risk area, to change the use mix, or to reduce the scale.

Where the installation itself is changing, the picture can change with it. Hazardous substances consents can be varied or revoked, quantities held on a site can fall, and the consultation distance is recalculated when they do. That is a long game, and on some regeneration sites it is the only game.

Major accident risk is also a topic the Environmental Impact Assessment Regulations 2017 require to be considered where a scheme is EIA development, so an Environmental Impact Assessment on a site near a hazardous installation should address it directly. An Environmental Statement must be prepared by competent experts, and an AI-drafted document is a starting point for that team rather than a substitute.

Designing to reduce the population at risk

The levers are simple and they are all about where people are and how many of them there are.

Put car parking, plant, storage and landscape in the part of the site closest to the installation, and occupied buildings furthest away. Keep vulnerable uses, which means anything involving children, the elderly or people who cannot self-evacuate, out of the higher risk zones entirely. Reduce the number of people rather than the number of square metres, since the assessment counts people. And avoid outdoor spaces designed to gather crowds within the inner zone.

Record the reasoning in the Planning Statement so that a case officer can see the design responded to the constraint rather than ignoring it. The discipline is the same as for other invisible constraints that only a search reveals, such as coal authority referral areas and what a search of contaminated land registers shows.

Enter the site postcode to see which reports it is likely to need.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

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