The Hidden Fire Risk on Construction Sites

Every year, construction site fires cause millions of pounds in damage, project delays, and—most tragically—injuries and fatalities. According to the Fire Protection Association, over 20% of construction fires are directly caused by hot work activities like welding, cutting, and grinding.

What makes these statistics even more concerning is that hot work fires are almost entirely preventable. The vast majority occur not during the work itself, but in the hours afterwards, when smouldering materials ignite after everyone has left site.

The Scale of the Problem

Recent data from CE Safety's analysis of Office for National Statistics records shows:

• 199 hot work-related fires in non-dwelling buildings across England in 2023/24
• Welding or cutting was the source of ignition in 85% of cases
• 32 incidents resulted in casualties or fatalities across the two-year period
• Many major losses occurred after the hot work was completed—sometimes hours later

Beyond the human cost, fire damage can devastate a construction project. Rebuilding costs, project delays, increased insurance premiums, and reputational damage can threaten a company's survival.

What Counts as Hot Work?

Hot work includes any activity that produces heat, sparks, or open flames. Common examples include:

• Welding: Arc welding, MIG, TIG, oxy-acetylene
• Cutting: Oxy-fuel cutting, plasma cutting, angle grinders
• Grinding: Metal grinding, cutting discs
• Brazing and soldering: Using torches or heat guns
• Torch applied roofing: Bitumen membrane installation
• Lead work: Lead welding on roofs and flashings
• Paint stripping: Using heat guns or blow torches

Legal Requirements

Hot work on construction sites is governed by several regulations:

Regulatory Reform (Fire Safety) Order 2005

Requires a fire risk assessment and implementation of fire safety measures. The 'responsible person' must take reasonable steps to reduce fire risk and ensure people can escape safely if a fire occurs.

CDM Regulations 2015

Imposes duties to prevent risk from fire. Principal contractors must coordinate fire safety across all trades on site.

HSE Enforcement

The Health and Safety Executive is the enforcing authority for fire safety during construction. They can issue improvement notices, prohibition notices, and prosecute where serious breaches occur.

Elements of an Effective Hot Work Permit System

1. Permit Application

Before any hot work begins, a permit must be requested and authorised. The permit should detail:

• The specific work to be carried out
• The exact location
• Start and finish times
• The name of the person carrying out the work
• Required precautions and PPE

2. Site Inspection

Before issuing the permit, a competent person should inspect the area to identify:

• Combustible materials within 10 metres (more for elevated work due to spark travel)
• Flammable liquids or gases
• Hidden combustibles (in walls, ceilings, under floors)
• Openings where sparks could travel to other areas
• Fire detection systems that might need isolation

3. Precautions

The permit should specify required precautions:

• Remove combustibles: Clear the area of anything that could catch fire
• Protect what can't be moved: Use fire-resistant blankets or screens
• Seal openings: Block gaps where sparks could travel
• Provide fire extinguishers: Appropriate types readily available
• Dampen down: Wet nearby combustible surfaces if appropriate
• Fire watch: A dedicated person to watch for fires during and after work

4. Fire Watch

This is perhaps the most critical element. A fire watch involves:

• A dedicated person monitoring for fire during hot work
• Continued monitoring for at least 60 minutes after work completes
• Fire extinguishing equipment immediately available
• Means to raise the alarm

Many serious fires have occurred because the fire watch period was cut short or not implemented at all.

5. Permit Close-Out

The permit isn't complete when the hot work finishes—it's complete when the fire watch period ends and a final inspection confirms no fire hazard remains.

Common Hot Work Fire Causes

Most hot work fires occur because:

• Safe working procedures weren't followed
• Hot work was done in an unsuitable area
• Combustible materials weren't identified or removed
• Permits were issued but precautions weren't implemented
• Fire watch period was too short or non-existent
• Sparks travelled further than expected (especially from elevated work)

Best Practice Recommendations

Before Hot Work

• Consider alternatives—can the work be done cold?
• Conduct hot work in designated safe areas where possible
• Issue permits for a specific task, location, and time period only
• Never permit hot work near active fire suppression systems without coordination

During Hot Work

• Keep the work area wet if circumstances permit
• Use fire blankets to contain sparks
• Have a fire watcher present at all times
• Ensure fire extinguishers are immediately accessible

After Hot Work

• Maintain fire watch for minimum 60 minutes (consider longer for high-risk situations)
• Check hidden areas where sparks might have travelled
• Don't leave site until final inspection is complete
• Consider thermal imaging to detect hidden hot spots

Conclusion

Hot work fires are devastating but preventable. A robust permit system, combined with proper precautions and—critically—adequate fire watch periods, can virtually eliminate this risk.

The extra 60 minutes spent on fire watch after completing hot work could save your project, your company, and potentially lives. It's not bureaucracy—it's essential protection against one of construction's most serious fire risks.