Guidance

Fire prevention plans: case study examples of alternative measures

Updated 11 January 2021

Fire prevention plans: case study examples of alternative measures

Read these case studies for examples of some of the alternative measures proposed by operators to show they could still meet the 3 objectives of our fire prevention plans guidance. These are to:

• minimise the likelihood of a fire happening
• aim for a fire to be extinguished within 4 hours
• minimise the spread of fire within the site and to neighbouring sites

No two sites are the same so each fire prevention plan is site specific. In the examples that follow, we decided that the site operators proposed alternative measures met these 3 objectives.

Case study 1: exceeding maximum pile sizes for pre-crushed waste wood

A waste wood operator wanted to store pre-crushed wood in pile sizes larger than the maximum sizes set out in our fire prevention plans guidance.

Testing for small fraction sizes and self-heating

The operator proposed storing the pre-crushed wood for 120 days. Due to concerns over mass self-heating the operator had carried out a particle distribution analysis (sieve test) on a sample of the pre-crushed wood. The results showed that more than 10% of the sample contained fraction sizes of less than 100mm.

Because the smaller fraction size can promote self-heating the operator sent a wood sample for isothermal calorimetry testing (basket testing). The test results indicated that the:

• critical ignition temperature of the sample was 107°C
• time to ignition was 200 days

As the operator proposed to store the wood for no longer than 120 days this provided reassurance that mass self-heating would not occur within that time frame.

In this case, the operator demonstrated that we could discount mass self-heating because of the proposed storage duration. However they still needed to take into account other common causes of fire so they also carried out the following.

Detecting hotspots and setting trigger temperatures

The operator carried out a visual waste acceptance procedure to screen out significant contamination that could pose a fire risk. They found that batteries and oily rags still ended up in the wood stacks. Contamination by batteries and oily rags is known to cause localised heating (hotspots), leading to fires.

The operator suggested using a thermal imaging system to detect hotspots within the pre-crushed wood stacks, with a trigger temperature of 75°C. As the material was at risk of mass self-heating and localised heating we considered that a maximum trigger temperature of 50°C would demonstrate appropriate control.

Good security measures

The site was manned 24 hours a day and 7 days a week (24/7) with security fencing and monitored CCTV providing full coverage of the site. These measures demonstrated appropriate control to reduce the risk of arson.

Reducing risks from hot exhausts

Vehicles were parked away from the stacks when not in use and washed down at the end of each shift. This reduced the risk of fire from wood dust coming into contact with hot exhaust pipes.

Early detection and reducing stack sizes

The stack sizes were larger than those set out in the fire prevention plan guidance. Therefore this posed an additional risk - it would be unlikely that a fire could be extinguished within 4 hours.

The operator suggested early detection using a thermal imaging system that would alert nominated staff by text, 24/7. Staff would be available 24/7 to use diggers and loading shovels to reduce the stack sizes to make sure a fire could be extinguished within 4 hours.

The operator provided a timed demonstration, including travel time taken for staff to arrive on site.

Case study 2: exceeding maximum pile sizes for processed wood

An operator wanted to store processed wood, in windrow formation, in pile sizes larger than the maximum set out in the fire prevention plan guidance. They proposed piles 6m high, 10m wide and 50m long, and stored for 90 days.

Testing for small fraction sizes

Due to concerns over mass self-heating the operator carried out a particle distribution analysis (sieve test) on a sample of the processed wood. The results showed that more than 10% of the material contained fraction sizes of less than 100mm. Because the smaller fraction size can promote self-heating the operator sent a wood sample for isothermal calorimetry testing (basket testing).

The isothermal calorimetry test results showed that the critical ignition temperature for the sample provided was 99°C and the time to ignite was 500 days. As the operator proposed storing the material for 90 days, we were satisfied that the risk from mass self-heating was acceptable. The material was unlikely to mass self-heat within that storage time period.

Although the isothermal calorimetry testing reassured us about the likelihood of mass self-heating, the operator still needed to address ignition due to localised heating (hotspots) and arson.

Detecting hot spots and setting trigger temperatures

The risk from localised ignition (hotspots) due to contamination is generally less likely in processed wood. This is because contaminants are removed before the processed wood is put into piles for storage. However a risk still remains.

To detect hotspots within the pile, the operator proposed using a temperature probe, and a hand-held thermal imaging camera, with a trigger temperature of 50°C. They would do this at the end of each working shift. If they recorded temperatures of 50°C they would dismantle the pile and remove it to the quarantine area to allow cooling to take place.

Good security

The site was secure and patrolled constantly by a security guard outside of normal working hours. These measures were appropriate controls to reduce the risk of arson.

The security guard used a hand-held thermal imaging camera and would monitor the piles for an increase in temperature. If they detected the trigger temperature of 50°C, they would alert the site operator and staff would come to the site. Staff would help with active firefighting by moving stacks and creating firebreaks.

This emergency plan had been tested with the local Fire and Rescue Service (FRS) present and we considered it to be effective.

Case study 3: exceeding maximum pile sizes for municipal waste

The operator of an energy from waste facility wanted to store municipal waste in bunkered storage. The facility consisted of an incinerator fed from the bunker by a series of hoppers.

The operator would store the waste for a maximum of 2 weeks before incinerating it on site.

The storage pile sizes were much larger than the maximum sizes set out in our fire prevention plan guidance.

Reducing the risk of self-heating

The bunkered storage area was monitored by a UKAS accredited thermal imaging system linked to a series of water cannons. The control room of the facility was staffed 24/7.

An overhead grab constantly moved the waste within the bunker to create a more homogenised material to improve the incineration process. As the waste was being constantly moved the risk of mass self-heating was reduced. The thermal imaging system was likely to detect any heating event.

Extinguishing a fire

The thermal imaging system was directly linked to water cannons which covered the entire bunkered storage area. The water cannons would automatically operate when a heating event was detected. Once extinguished, the overhead grab would remove the burnt material into the incinerator by a series of hoppers.

The operator proposed not having a quarantine area. Their firefighting strategy was to deal with any fire within the bunker and then to remove the burnt material to the incinerator.

The quantities of water available for firefighting were less than specified in the fire prevention plan guidance.

The short storage duration, continual waste movement and constant monitoring, greatly reduced the likelihood that a heating event would occur or go undetected.

Their firefighting strategy of using an overhead grab and installing water monitors reduced the risk of fire spreading within the waste bunker.

This all reassured us that fires could be extinguished within the 4 hour window.

Case study 4: exceeding maximum pile sizes for metal

A dockside storage site that stored metal wanted to store it in pile sizes larger than the maximum sizes set out in our fire prevention plan guidance.

They were going to store the metal in large fraction sizes with less than 2% contamination levels. The contamination was mainly from refractory material from construction and demolition activities, such as brick dust, glass and plaster.

Waste acceptance procedures and security

The waste acceptance procedures were appropriate to the risk. Contaminants present in the waste that could cause localised ignition (hotspots) were effectively screened out before the waste was brought on site.

The dockside site had good security measures and was patrolled regularly by dock security staff. The site was also monitored remotely by a CCTV system.

Due to the fraction size, contamination levels and the security measures in place the risk of ignition was low.

Extinguishing a fire

The site did not have enough firefighting water, as set out in our fire prevention plan guidance. However it had mains water and the hydrant was within 100m of the waste piles.

When the site was closed, there were enough staff on call to come to the site and operate plant and machinery to help the FRS as required.

All firefighting water was contained on site due to the site topography and drainage isolation system in place.

The FRS had confirmed that they would be able to use the dock water as a secondary supply and recirculate firefighting water if required.

Case study 5: separation distances of less than 6m

A site operator wanted to store waste in piles larger than the maximum pile sizes set out within the fire prevention plan guidance. They also proposed having separation distances between piles of less than 6m.

The site did not operate on a 24/7 basis but was monitored by CCTV with good security fencing.

The waste acceptance procedures were good and all contaminants that could lead to localised ignition were screened out before the waste was formed into piles.

As the waste was on site for less than 3 months, and effectively monitored, we considered that the risk of self-heating was low.

Installing fire walls

Keeping waste piles separated by at least 6m allows active firefighting to take place. This could not happen with the proposed reduced separation distance.

The site operator suggested installing a fire wall made from interlocking concrete blocks with the joints sealed with intumescent mastic. We found this solution acceptable for reducing the spread of fire between piles and allowing active firefighting to take place.

Water supply

The closest fire hydrant was more than 100m from the site and was therefore unsuitable as an initial water supply. The site was 50m away from a river and the site operator proposed using this as a suitable water supply. Although the river was affected by seasonal variation it was always deep enough throughout the year for use as an open water supply. The FRS confirmed that they would be able to use this as the supply in the event of a fire.