Traditional mechanical systems – like fire sprinklers and watermist systems that use bulbs – become less effective for life safety the slower a fire burns, according to new research.
This is because the longer it takes to build up the heat required to activate a sprinkler, the more toxic by-products are produced. This new data has been partially funded by Innovate UK Smart Grant and undertaken by Plumis, Ashton Fire and OFR Consultants who recently looked to explore the impact electronic activation could make on this hazard.
Tests demonstrated that concealed fire sprinklers activate two to 13 times slower than electronically controlled automatic watermist fire suppression systems for domestic fires.
The researchers developed a new test protocol for assessing active fire suppression systems against slow growing fires and were also able to create a fire engineering model which can be used to quantify the impact such systems have to survivability.
Yusuf Muhammad is co-founder at Plumis and co-authored the research
Yusuf Muhammad is co-founder at Plumis and co-authored the research, which was peer reviewed before being published, he commented: “Many domestic fires are slow burning and remain in the room of origin, but still produce significant amounts of toxic smoke. We know that the cause of death is more likely to be overcome by gas or smoke rather than the heat itself.
“We chose to develop a system concerned with suppressing fires in the early stages, that could also meet standardised fire tests which focus on fast growing fires. Speed of activation is very important for a vulnerable occupant, as they may be unable to move away from the heat source – which must reach a significant temperature to active a sprinkler, and has a direct impact on the Available Safe Egress Time (ASET).
“In conducting this research, we wanted to assess our system against tests beyond just the standardised test for watermist systems (BS8458) and produce the fires that our product is statistically more likely to be challenged with in real life.
“We also wanted to create solid data for fire engineers to use when specifying fire safety systems in new buildings. Peer reviewed studies provide information to aid industry understanding of the potential of these systems.”
To conduct the research, two series of enclosed fire experiments were carried out in an independent laboratory. The first series replicated the procedure in the BS 8458 standard, with the usual fuel package including an arrangement of plywood panels, foam, heptane and a wooden crib.
The second series included five experiments, using an identical fuel package. The key difference was to create a smouldering and slow-burning fire, which produces a high volume of toxic smoke but limited heat. This is the nature of a fire which may be typically caused by an electrical fault in domestic white goods. According to the research, for traditional sprinkler systems, this would be a challenging type of fire because it has a much longer insipid stage before it first ignites and because it is concealed within, for example, a refrigerator.
In each series researchers compared two fire suppression methods: concealed sprinklers and electronically activated nozzle watermist suppression systems. They measured the activation time of each system on both types of fire.
In the first series, the fast-growing fire as outlined in the British Standard test, performance of the two systems was comparable. When the fire reached high temperatures the electronically controlled nozzle watermist suppression system activated up to 84 seconds quicker than the concealed sprinklers.
The significant differences came when analysing the results of the second series of tests, which attempted to replicate a standardised fridge fire. In these tests, the concealed sprinklers activated 2.0 to 13.7 times slower than electronically controlled suppression systems.
Repeating the test in several different ways showed that the slower burning the fire, the bigger the activation gap. It also revealed certain types of fire where a concealed sprinkler would not activate at all.
In addition to the headline results, the research created a new repeatable test to simulate a slow burning domestic white goods fire. This detailed methodology is now available for the industry, so manufacturers can use this in their testing programmes, explains the authors.
Researchers have also used the data to create a model that predicts the point at which the suppression system will activate in this slower burning fire situation.
The findings of the research are said to provide fire engineers with the evidence they need to confidently represent watermist suppression systems in performance-based assessments – ensuring the best fire suppression solution is chosen.
According to Plumis, most products in the fire safety industry are designed for the median healthy occupant, which is not representative of wider society – only the able-bodied person who can escape from a fire if they need to. However the UK has an ageing population, and this brings some major challenges.
There are predicted to be over 1.5 million people with dementia in the UK by 2040. Around half of households in the social housing sector have at least one member with a long-term illness or disability.
In these sectors, products and systems that cater for those who are able-bodied are unlikely to provide enough support, and therefore earlier activation of fire safety systems can significantly benefit communities of vulnerable people, argues Plumis.
Yusuf added: “These research findings add to industry knowledge about slow growing fires, and we hope that others will access the data and use it in their testing processes. There is a major opportunity to raise the bar as we work together to improve fire safety because electronic activation can be applied to all systems. This direction of travel is evident in the latest edition of US standards for watermist systems NFPA 750 includes electronically controlled nozzles – making it the first global standard to embrace this technology.”
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