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Forensic analysis leads to new fire-fighting tactics

A breakthrough fire-fighting technique discovered during the third phase of waste fire tests carried out by the Waste Industry Safety and Health (WISH) group in October could enable waste sites to get fires under control before fire services arrive on the scene.

Preliminary results showed that use of a detergent and a particular fire-fighting technique could put out a blaze in less than three minutes.

Various fire-fighting methods were applied to a 27-tonne waste plastics fire burning in the open. This found that using water put out the fire (though not fully) in 30-40 minutes; compressed air foam took 10-20 minutes; and a ‘type A agent’ or detergent used with a particu­lar fire-fighting technique put the fire out in just 2 minutes and 27 seconds.

During the second phase of WISH’s fire tests – which investigated how waste fires burn – it was found that so-called vortices are the driver behind the extremely high temperatures expe­rienced in waste fires. Fire-fighters in the tests found that when they aimed their hoses at the base of the vortex, water was sucked in and then extin­guished the fire.

Chris Jones, chair of WISH, told MRW: “The phase two trials allowed us to understand what was mechanistically going on inside the fire – we were then able to develop our practical fire-fight­ing technique which exploited that knowledge.”

Jones credits the new technique to Angus Sangster, senior fire safety engi­neering manager at International Fire Consultants, who has been a lead figure in the trials.

Explaining the technique, Jones said:

“Providing the water does not form little droplets – which is where the [deter­gent] comes in – you just keep feeding it into the base of the vortex and the vortex does the rest for you. It distrib­utes [water] evenly across the fire, it takes out the heat, which knocks out the base of the fire triangle, and it goes out.”

According to a senior member of the fire services involved, this could mean that waste sites armed with a drum of the relevant material, a mixing valve and a team of people trained to use a fire hose could put out a blaze before the fire brigade arrived.

“These are fabulous outcomes,” Jones added. “It is something we now need to transfer into national operational guid­ance (NOG) for fire-fighters. We have to work through the analysis, explain the tactics and understand why it worked.”

With around 400 terabytes of data captured, the analysis will take some time. Each of the burn piles had a net­work of sensors within it to gather data.

According to Jones, it took some per­suasion of the fire-fighting teams not to spray the foam on top of the fire, because it is typically used as a smoth­ering agent.

Sangster explained that, alongside the phase three tests, he had been ana­lysing “several hundred fires during the past 15 years” to see “what went well and what didn’t go so well”, meaning that forensic analysis of past fires ran in par­allel with the live trials.

As well as fires burning in the open, tests were also conducted in concrete bunkers or bays, which are frequently used to store material at waste sites. These are considered a fire prevention measure to stop fire spreading and a way that sites can store more material on the same footprint, as well as reduce separation distances between stacks.

The testing found that, when 10 tonnes of plastic waste was burned in bunkers and the new fire-fighting tech­nique applied, the open fire was suppressed in less than six seconds. But in all cases, the waste was found to be still alight underneath.

He explained: “We had knocked down all the visible fire, so it was entombed or encapsulated and smoke is dramatically reduced. What we would then do is what you would do with any of these types of fires – you get a big piece of earth-moving machinery and you take out a bucket at a time and put it out a bucket at a time. It takes a while, but it is a very controlled process, does not affect the neighbours and doesn’t produce masses of fire water run-off.

“We used a tiny amount of additive during the two weeks of the trial [the detergent was used at 0.2% dilution compared with normal foams at 15- 19% dilution]. We used relatively little water – half an hour of water from the four pumps that didn’t put it out com­pared with the two minutes 27 seconds from two hoses on one pump that did put it out.”

At the start of the testing, reference burns with wood carried out in the bun­kers also gave interesting results.

“Wood in storage bays was very hard to burn in a sustainable fashion. You could get it to light, but then it would just smother itself. We had to change a number of the initiations for the later experiments because it is so hard to get a sustainable fire in a concrete bunker – so that in itself is [information] that we need to chase down and look at.”

Refuse-derived fuel burnt in loose piles into two bunkers, ignited from the inside and allowed to burn for 36 hours, also produced interesting results.

Jones explained: “We could see from the sensor array that there was a bulls­-eye of heat in both bunkers, with tem­peratures up to 400°C.

“The surface temperatures of the bunker waste was 25°C and, visually, there was no indication at all of a fire beneath. We got some indications from thermal imaging, but it was a lot less than we might have expected, and a lot lower level than is normally set as a trig­ger point for an alarm.

“So we need to go back and look at ‘how do we detect fire in waste mass?’ We believe we can use thermal imagery but it may require some further looking at exactly how effective it is and what temperature levels you have to set it at.”

A number of burns with plastic were also carried out. “We again got the result that we got in phase two, which has been questioned in some quarters,” Jones said.

“Plastics should burn at around 1,100°C – fire chemistry says that. But we saw it burning at 1,400-1,600°C – much, much hotter than had been anticipated or the theory predicted. It is the second time we have got that result, so we are very comfortable that is what temperature it is burning at.

“Probably this is something to do with air currents and vortices. As the stuff burns, it creates an air flow over itself which acts a bit like a mini-blast furnace, and that raises the tempera­ture.”

When waste plastic was burned in a concrete bunker with a 2m gap between the top of the waste and the top of the blocks – called a freeboard – flames were found to go up and over the free­board and down the other side. The current fire guidance from WISH sug­gests a 1m freeboard.

“So we need to look very carefully at freeboards, and in particular where concrete walls are being used as fire defences because we now know that fire will roll over it,” Jones said.

“Having said that, the thermal con­ductivity through concrete blocks was very low. And even having done two weeks of testing with them, they looked in good nick – so they are a good fire defence if properly set up.

“What I cannot tell you at the moment is what advice we are going to end up giving about this freeboard issue – we now know that fire will climb up and over even quite a high wall, so that is a problem.”

Working groups have now been reconstituted to formally consider the findings of the tests and work out how to translate them into guidance. An Institute of Fire Engineers group is being formed to create a new fire stand­ard, and WISH is talking to the National Fire Chiefs Council about how to pass the new knowledge through to NOG for the fire brigade.

“All of this has got to be peer-reviewed and the data fully analysed,” Jones said. “But on a practical level we have gone a long way, in terms of ‘how do you put out a waste fire without having people’s homes affected for hours and hours?’

“It is now Christmas 2017 and we have officially said that the three-phase project we laid out in 2013 has now come to an end. That doesn’t mean we stop needing to do more research but we have completed what we set out to do – it has taken a lot longer than we expected.”

He credits a “small team of individu­als” who have driven the project for­ward and the wider industry, including equipment suppliers, recyclers, the fire services and waste management com­panies, for contributing to the project which has cost more than £220,000.

Widespread interest in tests

chris jones

Chris Jones said the fire tests had prompted national and international inquiries.

“One of the things I never expected in the beginning of these tests was the level of interest in this work internationally as well as nationally. Everybody in the world seems to have a problem with waste fires.

“I have had emails and contact from people in Sweden, Germany, Australia, America – everybody wants to know what we achieved and what we are doing. Whatever it is we put in our guidance, there will be a lot of interest in it.”

“[The project] is a fantastic example of how industry and regulators can work together to find a solution to a problem if the will is there,” Jones said.

But while he praised the high level of engagement of the Fire Brigade and “great input” from National Resources Wales and the Scottish Environment Protection Agency, he admitted to a lack of involvement in the latest tests from the Environment Agency (EA): “[It has] chosen not to engage.”

In response, an EA spokesman told MRW: “The EA has supported fire tests by WISH from the outset and have given feedback on the project. We look forward to considering WISH’s final report when it has been peer-reviewed, and if it demonstrates practical ways to provide even greater public protection. Scientific research supports our revised guidance for producing fire prevention plans.”

As the team goes through the data, other findings are likely to emerge. As Jones told MRW: “This isn’t the end by any means.”

Waste fire tests – phase by phase

Phase one: Smaller scale laboratory-type waste burns were conducted at the Fire Protection Association research facility in Gloucestershire in late 2015. These provided baseline data on parameters such as burn rates and thermal heat outputs.

Waste tested: baled cardboard, baled LDPE plastic, baled HDPE plastic, baled refuse-derived fuel (RDF), baled solid recovered fuel (SRF), loose tyre crumb, loose screened wood chip, loose pre-crush wood, loose wood fines.

Phase two: Larger scale waste burns tests conducted at Pollington in Yorkshire and Barling in Essex in 2016. These involved much larger volumes of waste and aimed to replicate as closely as practical ‘real life’ waste fires. They revealed some of the different mechanisms at play during waste fires.

Waste tested: loose untreated (raw) wood waste, loose unscreened pre-crushed wood, loose screened pre-crush wood, loose wood fines, loose RDF, baled RDF, loose SRF, baled SRF, baled high-density plastic, baled low-density plastic, baled paper and card, loose frag fluff (plastics, foams and so on from dismantled end-of-life vehicles), shredded rubber (tyre).

Phase three: conducted at the Fire Service College at Moreton-in-Marsh, Gloucestershire, in October 2017. Focus was on fire-fighting and extinguishing fires, built on knowledge gained in the previous two phases. ‘Reference burns’ were conducted as well as two days of ‘major burns’ with Essex and East Sussex fire and rescue.

Waste tested: baled and loose plastics, baled and loose RDF (these represented the two ’classes’ of waste in terms of burns characteristics as identified in phase two); loose wood (as a reference standard).

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