Rubber and plastic fires – stopping the spread

As plastic and rubber waste increases across the globe, we are continually searching for alternative uses for these materials, which is seeing a rise in rubber and plastic recycling across the UK. This relies heavily on high volumes of storage and intense processing to repurpose the materials, both of which bring about significant fire risks – evidenced in the waste and recycling sector’s troubling fire record.

James Mountain, sales and marketing director, Fire Shield Systems, explores these fire risks and shares the measures that can be taken to mitigate them. 

As plastic has evolved over time, today’s plastics are built up of an unusually complicated mix of materials. The same is true for rubber, with today’s tyres containing over 200 different materials. Many of these ingredients used in modern plastics and rubber are combustible, meaning the fire risks associated with them are significant. 

Both plastic and rubber are oil-based materials, which can lead them to react much like flammable liquids when alight. This makes fire suppression incredibly challenging, and an understanding of the associated risks and mitigation measures key to ensuring safety.  

The rubber risk

When alight, the spread of smoke and fire from rubber can be rapid, burning at staggeringly high temperatures. Once it’s reached these high temperatures, rubber often begins to flow as a hot mass, which can entrap the flammable vapours being released from the material. This can catch fire with explosive force if not controlled quickly. 

Rubber also naturally repels water, meaning many extinguishing mediums will be shed and drained away. As such, traditional suppression systems, such as ceiling level sprinklers, will be limited in their ability to control the risk and fire spread. 

Tyre fires

Tyre fires are a very common type of rubber fire, as waste tyres are often stored for extended periods of time before recycling. These tyre stockpiles have the potential for high heat output, with the air spaces between them increasing risks further.  

When alight, tyres often burn for an astonishing amount of time. A key example of this is the 

Heyope Tyre Fire, which smouldered beneath the surface for an incredible 15 years before being fully extinguished in 2004. Burning tyres also release large volumes of oil, meaning water is often a less effective extinguishing material. 

When recycled, tyres are usually shredded into smaller chips, referred to as rubber crumb or tyre shred. This is a low-density material, which tends to be stored in stockpiles that are very 

susceptible to self-combustion. However, these fires will often take time to initiate, making prevention perfectly achievable in many scenarios. 

The plastic risk

Plastic flames often spread rapidly, as high as two feet per second, or 10 times that of wood on the surface. When alight, plastic will also melt and run, prompting the fire to spread in different and even unpredictable ways. 

When recycled, plastics are commonly used in the production of refuse derived fuel (RDF) and solid recovered fuel (SRF). This process carries key fire risks. Subcoal technology is also now being used to repurpose RDF and SRF to pellets, which can fuel lime or cement kilns, for example. These pellets have a high calorific value, meaning they can be highly susceptible to ignition. 

Responsibilities and regulations

The Environment Agency mandates that every waste site must have a clear fire prevention plan (FPP), which outlines all fire safety measures in place to mitigate the risks. The Regulatory Reform (Fire Safety) Order (2005) agrees with this, stipulating the reasonable steps that should be taken to mitigate fire risk. 

There is voluntary guidance pertaining to the relevant suppression measures for different materials (NFPA 11, EN 13565), and guidance specifically referencing the storage of rubber (ISO 2230:2002).

Reducing the risks

1. Initial bulk storage of raw materials 

• Minimise pile sizes and storage times
• Regularly monitor sub-surface temperatures
• Ensure sufficient ventilation
• Separate stockpiles – either physically or using fire walls. 

The oil-based run offs, as well as natural water-repellent properties, of rubber and plastic make water-based suppression solutions unsuitable. Compressed air foam systems are often more effective, as the agent sticks to the materials, eliminating oxygen supply. 

2. Processing

• Carry out regular maintenance on all machinery to monitor friction or avoid mechanical failure
• Regularly clean all machinery to prevent the build up of combustible particles. 

Certain parts of the processing machinery may need localised protection. Detection systems, such as video or infra-red flame detection, can help to monitor for flames, embers or sparks. 

3. Storing processed materials

• Rotate stockpiles where risk of combustion is high
• Monitor temperatures regularly below the material surface
• Control any material risks, such as exposed metal content. 

Water alone will often be ineffective in suppressing fires for RDF or SRF, due to its high calorific value. For this application, Class A penetrating foam systems, with cannons, hose reel or deluge systems, will often be more effective. This method focuses suppression towards a particular area or hotspot, penetrating the surface to suppress at point of ignition. 

Your fire mitigation measures should be informed by a full fire risk assessment, which will ensure your solution is tailored to your site’s individual risks. 

For more information visit http://bit.ly/fire-shield-systems-ltd or call 0800 975 5767.