A zone drawing can look reassuringly definite. Coloured boundaries, zone numbers and equipment references give the impression that a complicated risk has been reduced to a clear plan. Yet every line on that drawing depends on decisions made elsewhere: which substances are present, where they could be released, how ventilation behaves, what happens during cleaning or maintenance, and which assumptions were used to define the extent of the hazardous area.

That is why a good DSEAR zone drawing should never sit alone in a project folder. It is the visible result of a connected body of work, beginning with the risk assessment and hazardous area classification, then carrying through into equipment selection, installation, verification, inspection and change control. When those links are clear, the drawing becomes a practical tool for people working on the site. When they are missing, even an attractive plan may be difficult to rely on.

What DSEAR actually requires you to record

The Dangerous Substances and Explosive Atmospheres Regulations 2002 require an employer to make a suitable and sufficient assessment where a dangerous substance is, or is liable to be, present at work. The assessment must consider the substance's hazardous properties, the way work is carried out, the likelihood and persistence of an explosive atmosphere, possible ignition sources, the anticipated effects of a fire or explosion, and connected places that may also be affected.

Where an employer has five or more employees, the significant findings must be recorded. If an explosive atmosphere may occur, those records must include enough information to show which places have been classified into zones, the relevant safety equipment, any required verification of overall explosion safety, and the arrangements for coordination where more than one employer shares the workplace.

Many organisations bring this material together in a DSEAR file or an 'explosion protection document'. That can be a very effective structure, but the title is not the important part: DSEAR does not prescribe one universal UK form or template carrying that name. What matters is that the required findings and supporting evidence are coherent, current and usable. A drawing with no traceable assessment behind it is not a substitute for that record, just as a long report with no practical drawing may be hard for a maintenance team to apply.

Start with the process, not the drawing

Hazardous area classification begins with the real process. That includes the materials present and their relevant properties, but it also means understanding quantities, temperatures, pressures, containment, possible interactions and the ways in which a release could occur. Normal production is only part of the picture. Sampling, filling, emptying, changeovers, cleaning, drainage, breakdowns and maintenance can create conditions that do not appear on a simplified process description.

The HSE's current overview of DSEAR makes the wider duty clear: employers must identify dangerous substances, eliminate or control the risks where possible, mitigate the effects of an incident, prepare for emergencies, train people and identify places where explosive atmospheres may occur. Zoning supports those duties; it does not replace them.

This is also where the right range of competence matters. The people who understand a process, its substances and operating deviations may not be the same people who understand ventilation, explosion protection or Ex electrical equipment. On more complex sites, a dependable assessment is usually built through cooperation between operations, process safety, engineering, health and safety, maintenance and appropriately competent specialists. General guidance can explain the structure, but the conclusions must be based on the actual plant and conditions.

How the risk assessment becomes a DSEAR zone drawing

DSEAR requires places where an explosive atmosphere may occur to be classified as hazardous or non-hazardous, with hazardous places then assigned to zones. Under Schedule 2 of the Regulations, Zones 0, 1 and 2 apply to explosive atmospheres formed by gas, vapour or mist, while Zones 20, 21 and 22 apply to combustible dust clouds. The distinction is based on how frequently the explosive atmosphere is expected and how long it persists, not on a simple measure of how serious an incident could be.

For gases, vapours and mists, Zone 0 describes an atmosphere present continuously, for long periods or frequently; Zone 1 covers one likely to occur occasionally in normal operation; and Zone 2 covers one not likely in normal operation and, if it occurs, present only for a short period. The dust-zone definitions follow the same pattern for Zones 20, 21 and 22. Published rules of thumb sometimes attach annual hour ranges to these descriptions, but HSE notes that no such time limits have been officially adopted. A site-specific assessment should therefore apply the legal definitions and the relevant technical method rather than treating an informal threshold as the rule.

The assessor then determines where the zone extends. Release characteristics, operating conditions, the degree and availability of ventilation, and likely dispersion all affect that conclusion. A flat plan alone may not be enough. Vapour or dust can extend above or below the source, enter an enclosure, collect in a low point or move through an opening, so elevations, sections or detail drawings may be needed to make the classification unambiguous.

What a good DSEAR zone drawing should show

The exact format should suit the site and the classification method used, but a useful drawing normally gives a competent reader enough information to understand the conclusion and find the evidence behind it. Depending on the process, that may include:

• A controlled identity. The site and area, drawing number, revision, date, scale, orientation, legend and status, so nobody has to guess whether they are using the approved version.
• Plant and release points. The relevant vessels, pipework, vents, transfer points, dust-handling equipment or other features that anchor the classification to the physical process.
• Zone type and three-dimensional extent. Clear boundaries in plan, with elevations, sections or stated heights and depths where they are needed to describe the classified volume.
• Traceable references. Links to the hazardous-area classification data sheets, substance information, calculations, ventilation assumptions and the DSEAR risk assessment from which the drawing was produced.
• Conditions and limitations. The operating mode, ventilation status or other assumptions on which the zones depend, including any temporary or transient arrangements that need separate controls.

Clarity is more valuable than decoration. If several colours are used, the drawing still needs to work when printed or viewed by someone with colour-vision deficiency, so line styles, hatching and a clear legend can be important. Conversely, a crowded drawing that tries to contain every calculation and equipment detail may become unreadable on the factory floor. The supporting data sheets and registers can carry the depth, while the drawing provides the controlled spatial view.

Connect the zones to equipment and verification records

A zone identifies where special precautions are needed; it does not, by itself, specify every item that may be used there. Equipment selection also depends on the substance and atmosphere, the equipment's protection concept and certification, temperature considerations and the particular installation. The HSE's guidance on electricity in potentially explosive atmospheres emphasises that equipment and installations in these locations need to be designed and constructed to eliminate or reduce ignition risk, then inspected and maintained by competent people.

Good documentation therefore connects the zone drawing to an equipment register, selection evidence, certificates and installation records. It should also recognise that ignition control is wider than electrical equipment. Hot surfaces, static discharge, mechanical friction, vehicles and maintenance activities can all be relevant, which is why a DSEAR file should communicate with permit-to-work arrangements, operating procedures and the site's wider control measures.

Before a workplace containing hazardous places is used for the first time, DSEAR requires its overall explosion safety to be verified by a person competent in explosion protection through experience, professional training or both. That verification is not simply a signature on the zone drawing. The record should make it possible to see what was reviewed, what evidence supported the conclusion, what actions remained open and how completion was confirmed.

Make change control part of the document

A zone drawing captures a set of conditions at a point in time, and industrial sites do not stand still. A new solvent, altered cleaning regime, faster filling rate, enclosure around a machine, moved extraction inlet or revised maintenance method can change the assumptions behind the classification. Even a wall or door installed outside the immediate process may alter natural ventilation and therefore affect the zone extent.

DSEAR requires the risk assessment to be reviewed regularly so it remains up to date, particularly when there is reason to think it is no longer valid or when the workplace, process or organisation undergoes a significant change, extension or conversion. It does not set a universal annual renewal date. The practical answer is to connect hazardous-area records to the site's management-of-change process, so the DSEAR assessment is considered before a modification is approved, not rediscovered after installation.

When a change is material, the update should travel through the whole chain: risk assessment, classification data, zone drawing, equipment selection, design, inspection plan, operating procedures and training where relevant. Updating only the drawing can leave the rationale behind it out of step; updating only the report can leave contractors working from an obsolete plan.

Documentation that earns its place on the factory floor

The strongest DSEAR documentation is not produced solely for an audit. It helps a project engineer decide where a junction box can be installed, gives maintenance teams the right starting point before opening equipment, supports procurement when replacements are specified, and helps contractors understand where their tools, vehicles or temporary equipment may introduce an ignition source. It also provides a common reference when operations, safety and engineering teams need to discuss a proposed change.

Access must still be controlled sensibly. The master documents need clear ownership and revision control, while the people making decisions on site need the current information in a usable form. Superseded drawings should be removed from points of use or clearly archived, and mark-ups created during a project should be incorporated into the controlled record rather than left as the only evidence of what changed.

How AES can support a hazardous-area review

AES supports manufacturing and industrial businesses with hazardous-area classification, design, installation, verification, inspection and maintenance. Its CompEx-accredited team can help connect an agreed DSEAR assessment and zone classification to the electrical work on site, including equipment selection, installation quality, inspection findings and the documentation needed for a clear audit trail.

That work should sit within the employer's wider DSEAR responsibilities. A complete assessment may require detailed process knowledge and specialist input on substances, dusts, ventilation or explosion protection, depending on the site. AES can work with the client's responsible people and other competent specialists so that the electrical solution reflects the approved classification and remains practical to operate and maintain.

If your zone drawings no longer match the plant, the supporting classification data is difficult to find, or planned changes could affect a hazardous area, a structured review can identify where the evidence has become disconnected. AES can help you assess the electrical and documentation gaps, agree a proportionate scope and plan the work around operational requirements.

FAQs

What is a DSEAR zone drawing?

A DSEAR zone drawing is a controlled plan, elevation or set of details showing where explosive atmospheres may occur and how those places have been classified. It should be traceable to the hazardous-area classification and DSEAR risk assessment, rather than treated as a standalone diagram.

Is a zone drawing a legal requirement?

DSEAR requires employers to classify places where explosive atmospheres may occur. Employers with five or more employees must record the significant findings, including sufficient information to show which places have been classified into zones. The Regulations do not prescribe one drawing format, but HSE guidance says classification conclusions should be supported by appropriate reference drawings showing zone extents, including above and below plant where relevant.

What is the difference between a DSEAR risk assessment and a zone drawing?

The risk assessment considers the dangerous substances, work activities, potential releases, ignition sources, consequences and controls. The zone drawing records the spatial outcome of the hazardous-area classification. It is one part of the evidence generated by the wider assessment, not a replacement for it.

How often should DSEAR zone drawings be reviewed?

There is no universal annual interval in DSEAR. The risk assessment must be reviewed regularly to keep it current, and particularly when it may no longer be valid or there has been a significant change. Zone drawings should be checked and updated whenever a review changes the classification or its assumptions.

Does Zone 2 mean the consequences are minor?

No. The zone describes the expected frequency and duration of an explosive atmosphere, not the potential severity of an incident. Consequences and the suitability of control measures still need to be considered in the wider risk assessment.