Construction Hot Works Fire Safety: CDM 2015 & Rooftop Hazards

Carrying out hot works at height carries severe fire risks that require strict operational controls. When thermal processes like welding, cutting, or brazing take place near combustible building materials, a small spark can rapidly escalate into an uncontrolled blaze. Working on a roof compounds these dangers through restricted access, limited evacuation routes, and the obvious practical difficulties of fighting a fire at height. Maintaining construction hot works fire safety relies on strictly meeting statutory duties, conducting thorough pre-start planning, and maintaining active site supervision to ensure safety management systems actually work on the ground.

The Staines Rooftop Blaze: A Case Study in Hot Works Failure

On 26 July 2024, a major fire broke out on the roof of a 14-storey apartment building under construction at the Old Telephone Exchange development in Staines-upon-Thames, Surrey. Four subcontractors, working under the control of C Watkins Plumbing Limited, were installing an air source heat pump on the roof when sparks from welding work ignited uncovered rigid foam insulation laid across the surface. The fire quickly became a self-sustaining blaze that spread across the entire roof space, burning until the available fuel was completely consumed.

The four operatives faced an immediate life-safety crisis. Their only way off the roof was a single opening in the floor leading down a ladder to Level 14. There was no secondary escape route, no way to raise a fire alarm from the roof, and no fire extinguishers at the work area. While the workers evacuated without reported injuries, Health and Safety Executive (HSE) inspector Stephanie Hickford-Smith noted how close they came to disaster: “Had the fire started closer to their escape route, or had they not acted as quickly as they did, the outcome could have been devastatingly different.”

An HSE inspector who happened to be nearby documented the incident in real time, photographing the building ablaze, while the Surrey Fire and Rescue Service recorded the subsequent damage. A formal investigation revealed systemic procedural failures: no permit to work had been issued for the welding, and although C Watkins Plumbing Limited had corporate safety policies requiring risk assessments and method statements (RAMS) for hot works, none had been prepared for this project.

The HSE brought criminal proceedings through senior enforcement lawyers James Towey and Laura Lax, alongside paralegal officer Farhat Basir. At Staines Magistrates’ Court on 29 October 2026, C Watkins Plumbing Limited—registered at Watkins House, Leigh Road, Haine Industrial Park, Ramsgate, Kent—pleaded guilty to breaching Regulation 15(2) of the Construction (Design and Management) Regulations 2015. The court fined the contractor £20,000 and ordered them to pay £8,270 in prosecution costs.

Structural Risk Analysis & Legal Breach Summary

Regulatory Mandate: CDM 2015 and Contractor Duties

The primary statutory standard governing contractor safety during construction operations is the Construction (Design and Management) Regulations 2015. Under Regulation 15(2), contractors must plan, manage, and monitor construction work under their control to ensure, so far as is reasonably practicable, that it is carried out without risks to health and safety.

This duty is active and continuous. Contractors must establish safe systems of work before operations begin, verify that necessary physical precautions are in place on site, and supervise execution to prevent dangerous shortcuts. The court’s finding against C Watkins Plumbing Limited hinged directly on the company’s failure across all three elements: planning was absent due to the lack of risk assessments, management failed because work started without required permits, and monitoring lapsed entirely, allowing high-risk welding directly over exposed combustible insulation.

An employer cannot satisfy Regulation 15(2) simply by keeping safety manuals or written policies on file. When internal rules require permits and risk assessments, failing to put those procedures into practice on site demonstrates a complete breakdown in management and supervision, directly supporting a statutory conviction.

Technical Hazards: Combustible Materials and Ignition Sources at Height

Hot works generate heat through open flames, electric arcs, conductive heating, and expelled molten slag or sparks. Welding operations throw spatter several metres from the work site, carrying enough heat to ignite combustible materials immediately on contact or after an undetected smouldering period.

Rigid foam insulation panels laid across flat roofs pose a major fire risk when left unprotected during hot works:

• Low Ignition Threshold: Uncovered rigid polymer foam insulation exposed to molten slag can catch fire almost instantly, without needing prolonged contact with a flame.
• Rapid Surface Spread: Continuous, uninterrupted insulation across flat rooftop spaces forms an ideal fuel bed. Once ignited, flames sweep rapidly across the roof plane.
• Self-Sustaining Combustion: Rigid foam fires generate intense heat release rates and quickly become self-sustaining, burning fiercely until the fuel layer is consumed.
• Smoke Generation and Egress Impairment: Burning foam produces thick, toxic smoke that rapidly destroys visibility and air quality, creating an acute hazard for workers trying to reach ladders or floor openings.

Critical Safety Deficiencies: Systemic Failures at Height

The Staines rooftop fire illustrates how administrative oversights and physical site failures combine to create high-hazard environments during construction.

Absence of a Permit-to-Work (PTW) System

A Permit-to-Work system acts as a crucial administrative safety check before high-risk work begins. For hot works, a PTW requires a competent supervisor to inspect the workspace beforehand to verify that combustibles are removed or shielded, fire blankets are deployed, firefighting equipment is staged, and clear emergency procedures are established. In the Staines incident, no permit was ever issued. Work started without checking physical controls, leading directly to welding over exposed, flammable insulation.

Failure to Implement Risk Assessments and Method Statements (RAMS)

Although C Watkins Plumbing Limited had written corporate policies requiring task-specific RAMS for hot works, none were produced for this job. Project-specific RAMS identify local hazards, define safe working distances, specify protective coverings, and set out clear emergency protocols. Failing to assess the work meant that no practical control measures were selected, engineered, or deployed on the roof.

Single Point of Failure in Rooftop Egress

Emergency egress from height requires secondary escape options. Four subcontractors on a 14-storey roof relied entirely on a single hatch and ladder down to Level 14. Had the fire ignited near that hatch, or had wind driven flames across it, the workers would have been trapped. Escape routes must always account for potential fire spread and smoke travel, providing alternate ways off the roof.

Absence of Warning and Firefighting Equipment

The rooftop lacked any equipment to raise an alarm or fight a fire:

• Alarm Provision: Without call points, temporary wireless alarms, or reliable radio links to the site safety team, raising an alarm depended entirely on workers shouting or using personal phones.
• First-Line Firefighting: The complete lack of portable fire extinguishers removed any chance of putting out sparks or small flare-ups early, allowing the initial ignition to grow into a full-scale rooftop fire.

Practitioner Framework: Pre-Hot Works Rooftop Compliance Checklist

To comply with Regulation 15(2) and follow good practice, site supervisors and contractors should complete a thorough check before striking an arc or applying heat near rooftop installations.

1. Substrate and Environmental Clearance:

   Inspect all surfaces within a 10-metre radius of the planned work. Clear away combustible debris, solvents, and packaging. If combustible roofing membranes or rigid foam insulation cannot be removed, cover them completely with heavy-duty fire-retardant blankets to protect them from sparks and slag.

2. Permit-to-Work Verification:

   Confirm that an authorized, site-specific Hot Works Permit has been signed and issued by the site manager or designated duty holder. Check that the permit states the exact location, duration, assigned operatives, and required safety controls.

3. Dedicated First-Line Extinguishment:

   Place inspected, suitable portable fire extinguishers directly adjacent to the work area. A typical setup includes at least one pressurized water or foam unit alongside a carbon dioxide or dry powder extinguisher suitable for electrical risks.

4. Reliable Alarm Signalling:

   Verify that operatives have a direct, tested way to trigger the site fire alarm from the roof. Options include linked wireless temporary call points, site radios tuned to emergency channels, or tested siren systems.

5. Redundant Egress Inspection:

   Ensure there are at least two clear, unobstructed escape paths from the roof workspace. Keep floor hatches, access doors, and vertical ladders completely clear of storage, hoses, leads, and flammable materials.

6. Post-Work Fire Watch Protocol:

   Assign a trained individual solely to fire watch duties during hot works. Maintain this continuous watch for at least 30 to 60 minutes after hot operations finish, checking for smouldering, hot spots, or heat transfer along roof decking and service penetrations.

Regulatory Clarification: Statutory Duties vs. Technical Guidance

Maintaining compliance requires understanding the distinction between legal requirements under statutory law and technical guidance published by safety regulators.

The mandatory legal duty enforced in the Staines prosecution comes directly from primary legislation: Regulation 15(2) of the Construction (Design and Management) Regulations 2015. Breaching this statutory duty is a criminal offence, exposing commercial entities to unlimited fines in court.

By contrast, HSG168 – Fire Safety in Construction is guidance published by the Health and Safety Executive. While HSG168 is not law itself, it sets the recognized standard for industry compliance. The guidance highlights that:

• Fire precautions must be considered during design and procurement, then implemented effectively during construction.
• Risk assessments must account for high-risk processes that can accelerate fire spread, as well as complex evacuation paths.
• Duty holders must review and update risk assessments and physical controls throughout the project as conditions change.

In court, prosecutors use failures to follow HSG168 to demonstrate that a contractor failed to take reasonably practicable steps to control risk, helping establish a breach of CDM 2015 Regulation 15(2). Duty holders who ignore published guidance risk regulatory action and substantial financial penalties.

Proactive Safety Management for High-Risk Rooftop Activities

The Staines-upon-Thames fire clearly demonstrates the danger of treating fire safety management as a mere paperwork exercise. Detailed corporate safety manuals mean nothing to site workers if those controls are never executed on the ground. High-risk activities at height require active, continuous oversight.

Contractors and project managers must ensure that high-temperature operations, combustible insulation, and restricted access paths are controlled rigorously. Implementing formal Permit-to-Work procedures, confirming secondary escape routes, providing working fire alarms, and enforcing continuous fire watches are basic prerequisites. Working with diligence ensures construction operations proceed safely, fulfilling legal duties while protecting site workers from preventable harm.

Case and prosecution data sourced from the Health and Safety Executive: HSE Media Centre Press Release: Aftermath of apartment roof blaze workers ‘lucky to escape’ from.