Success of ‘bucket brigades’ to fight fires depends on water flow
Article by Alec Basson (Corporate Communication)
People in informal settlements are often forced to use the bucket brigade technique (passing buckets of water from one person to another) to suppress a shack fire. Fires develop so fast that even a fire truck ready-and-waiting at a station near to an informal settlement will not reach a fire before a home is destroyed. Research conducted at Stellenbosch University (SU) found that the effectiveness of a bucket brigade hinges on fully operational and accessible communal standpipes being available (water supply points) and the rate at which water flows from these pipes.
“In case of emergency, bucket brigades can help to extinguish or reduce the spread of fires, but this is often hampered by the lack of a sufficiently reliable water supply,” says Prof Richard Walls from SU’s Department of Civil Engineering. He and Master’s graduate Stefan Löffel conducted a study on different techniques for suppressing fire, along with water application rates required for people to suppress fires in informal settlements, as part of a bigger study on improving informal settlement fire safety. The findings of their study were published in the international journals Fire and Materials and the International Journal of Disaster Risk Reduction recently.
Pointing to previous research and firefighter experience, which have shown that water application through ‘bucket brigades’ can help to suppress fires, or at least slow them down, Walls says they wanted to develop a preliminary model for quantifying the amount of water and supply rate needed to suppress fires of various sizes using bucket brigades. This can help answer questions such as: How much water is needed? Is current water infrastructure sufficient? What can be done to improve bucket brigades when sufficient water is not available (as it often isn’t)?
To do this, they constructed structures similar to shacks in informal settlements and conducted a series of full-scale burnout experiments at the Epping Fire and Rescue Training Academy in Cape Town using the bucket brigade technique. The City of Cape Town, Breede Valley Fire Brigade and the Western Cape Disaster Management Fire & Rescue Service have been very active in assisting such research to try combat informal settlement fires. Head of the Epping Training Academy, Clinton Manuel, and his team, supported the work to try finds additional ways of dealing with the ongoing challenges fire departments have with these fires.
To create a repeatable fire experiment a fuel load of 25 kg/m2 of South African pine was placed inside the structure and set alight. The fire was then allowed to develop until “flashover”, i.e. entire room engulfed in flames coming out the door and window. Various different products were used to try to suppress the fire in different experiments, along with water buckets. For the bucket experiments – after buckets of water were applied to the fire, the buckets were transported back to the water supply point where the process was repeated, with water application occurring at specific rates. Computer models were developed to analyse the experiments and understand how to suppress such fires.
Sufficient discharge rate
“Our experiments and computer models showed that a discharge rate of about 23 to 40 litres per minute (lpm), as provided by a 15 mm diameter tap with reasonable pressure, would, in many cases, be sufficient to suppress a fire, providing that: a single dwelling is burning, and all water is transferred to it,” says Löffel.
“At this rate, it takes approximately 12 to 21 seconds to fill a bucket with eight litres of water. However, if many people open taps all at once, water is lost whilst being transferred to the home that is burning, or the fire spreads quickly to other drawings, then more water is required.”
“However, you will not suppress most fires at a supply rate of 10 lpm or less, since the time needed to fill a single bucket with eight litres of water increases significantly to 48 seconds. In such instances, the fire grows faster than the water can suppress it.
“The discharge rate of 23 and 40 lpm is suitable for fire sizes of around four megawatts (MW), based on a dwellings of 2,4 x 3,6 x 2,4 metres with 25kg/m2 of wood in it. Most informal homes with beds, cloths, furniture, and carpets will produce a fire of around 4 MW, but for larger dwellings or homes where there is lots of furniture and open windows these can have fires of 7 MW or more. In communities with a single standpipe with flow rates less than 23 lpm, fires greater than four MW cannot be suppressed in time without resulting in substantial fire spread to adjacent homes.”
Walls points out that guidelines prescribe the provision of a single standpipe with a minimum discharge rate of 10 lpm for 25 to 50 shacks which means it will take longer to suppress a fire, allowing it to spread quickly to adjacent shacks.
“The time required to extinguish a dwelling fire increases significantly as the water discharge rate at the standpipe is reduced.”
Walls says the effectiveness of the bucket brigade technique is inversely proportional to the number of shacks affected by a fire as well as the distance between the standpipe and the burning shacks.
“This is a concern because informal dwellings are predominantly constructed from combustible materials which means the fire will spread to adjacent dwellings before the first bucket of water is applied to the dwelling where the fire started.”
Walls recommends that where possible residents in informal settlements always have a bucket filled with water in their dwelling at all times, thereby potentially extinguishing a small fire before it gets out of hand (but this should be done considering hygiene and drowning risks for children). People can then also assist neighbours whose homes have caught alight.
He adds, however, that a fully operational fire brigade remains the most effective way of extinguishing multi-dwelling fires.
Walls says the findings of their study would be applicable to many low-income countries with informal settlements.
“Based on the findings, the team is working with local fire stations to develop additional community training interventions, following on from excellent work done by many NGOs and fire stations in the past.”
- Source: Löffel SA, Walls RS. Determination of water application rates required for communities to suppress post-flashover informal settlement fires based on numerical modelling and experimental tests. Fire and Materials 2020: 1–15. https://doi.org/10.1002/fam.2825
Benchmarking fire suppression systems
In a related study, published in the International Journal of Disaster Risk Reduction 45 (2020), Löffel and Walls proposed a full-scale fire testing methodology that can be used to benchmark various fire suppression systems against each other and to help decision-makers choose the most suitable interventions to combat fires in informal settlements. The methodology can be carried out without the need for sophisticated equipment, making it readily available to fire brigades and municipalities.
- Source: Löffel SA, Walls RS. Development of a full-scale testing methodology for benchmarking fire suppression systems for use in informal settlement dwellings. International Journal of Disaster Risk Reduction 2020;45:101451. doi:10.1016/j.ijdrr.2019.101451.
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Prof Richard Walls
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