Rubber and plastic fires – stopping the spread
As rubber and plastic waste grows, we are continually looking for alternative uses for these materials. Across the UK, this is seeing a rise in rubber and plastic recycling. However, this relies heavily on high volume storage and intense processing, as the materials are repurposed for new uses, including renewable fuels and construction materials. This brings about key fire risks – demonstrated by the UK’s troubling fire record for waste and recycling.
James Mountain, Sales and Marketing Director, Fire Shield Systems, discusses the various fire risks associated with rubber and plastics, and the measures that can help to mitigate these risks.
As plastic technology has developed, it has created an unusually complex family of materials. Similarly for the rubber industry, today’s tyres comprise over 200 different raw materials. Many of these ingredients used in modern rubber and plastics are combustible, amplifying the materials’ fire risk.
Both rubber and plastic fires are oil-based, which can cause them to react like a flammable liquid when ignited, making fire suppression extremely challenging. This makes understanding and mitigating all of the associated risks key to ensure safety.
The rubber risk
When rubber ignites, the spread of smoke and fire can be rapid, burning at incredibly high temperatures. At these high temperatures, rubber begins to flow as a hot mass, emitting flammable vapours that can become trapped in the molten rubber. If not controlled quickly, this can catch fire with an explosive force.
Rubber also naturally repels water, causing many extinguishing mediums to be shed and drained away. This means traditional suppression measures, such as sprinklers at ceiling level, will often be limited in their ability to control rubber fires.
Tyre fires are the most common kind of rubber fire, as waste tyres are piled and stored for long periods before being recycled for rubber crumb or tyre shred. These stockpiles of tyres have a potential for high heat output, and the air spaces present between tyres increase the risks further.
Tyre fires often burn for an incredible amount of time. One key example being the Heyope Tyre Fire, which took an unbelievable 15 years to fully extinguish, as tightly packed tyres enabled the blaze to smoulder under the surface. Burning tyres release large quantities of oil, making water a less effective extinguishing material.
When recycled, tyres are often shredded into smaller chips, which creates a low-density material, stored in stockpiles that are highly susceptible to self-combustion. However, these stockpile fires often take weeks to initiate, meaning prevention is perfectly possible in many scenarios.
The plastic risk
The rate of burn for plastics can vary widely, depending on the type and flame retardant chemicals present. Generally though, plastic flames spread rapidly, as high as two feet per second, or 10 times that of wood on the surface. Like rubber, at high temperatures, plastics will melt, causing fire spread in different and unpredictable ways.
Plastics are also commonly used for the production of solid recovered fuel (SRF) and refuse derived fuel (RDF), a process which carries significant fire risks. Subcoal technology is now being applied to upgrade those fuels into pellets, which can be used to fuel lime or cement kilns, for example. As these pellets have a high calorific value, they are highly susceptible to ignition.
Responsibilities and regulations
According to the Environment Agency (EA), every waste and recycling site must have a clear fire prevention plan (FPP) in place, that outlines its fire prevention measures and policies. The Regulatory Reform (Fire Safety) Order (2005) also outlines business owners’ role in ensuring reasonable steps are taken to mitigate fire risk.
When it comes to rubber specifically, there is voluntary guidance surrounding storage (ISO 2230:2002) and suppression measures (NFPA 11, EN 13565).
Reducing the risks
- Initial bulk storage of raw materials
• Regularly monitor temperatures below the material surface
• Control moisture levels
• Ensure adequate ventilation
• Minimise pile sizes
• Ensure separation between all stockpiles
• Manage stock to prevent prolonged storage.
Due to natural water-repellent properties and oil-based run offs, water-based solutions for fire prevention or suppression are ineffective for plastics and rubber. Instead, you may want to consider applying a compressed air foam system, which allows the agent to bind to the materials, removing oxygen supply.
• Conduct regular, planned maintenance of all machinery and equipment to monitor for friction or mechanical failure
• Frequently clean all machinery and equipment to reduce buildup of combustible particles.
Certain parts of the processing equipment may need localised application protection, and detection systems, such as infra-red or video flame detection, which can also help to monitor for sparks or embers.
- Storing processed materials
• Turn stockpiles frequently where risk of self-combustion is high
• Regularly monitor sub-surface temperatures
• Control moisture levels
• Control material risks – eg exposed metal content.
Due to its high calorific value, water alone will often not be effective in suppressing fires for SRF or RDF. Here, Class A penetrating foam systems, using cannons, deluge or hose reels systems, will likely be more effective. This focuses suppression on a particular area or hotspot, reaching below the surface to suppress at the point of ignition.
Any fire mitigation measures should be supported by a full fire risk assessment to ensure the solution is tailored to the individual application. This will account for multiple considerations, including the quantity of material stored, its form and the processing activity, to ensure solutions are effective in mitigating risk.
For more information visit http://bit.ly/fire-shield-systems or call 0800 975 5767.