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- Meraner, Christoph, et al.
(författare)
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Effektiv, skånsom og miljøvennlig slokking av brann i mindre bygningsenheter
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This study evaluates efficient, low-exposure and environmentally friendly extinguishing of fires in small building units and is commissioned by the Norwegian Directorate for Civil Protection (DSB) and the Norwegian Building Authority (DiBK). The main objective is to increase the knowledge on how to extinguish fires in smaller building units efficiently in terms of time and water amount, with minimal exposure of the fire service to smoke, heat and direct contact with soot, as well as minimal environmental exposure in case of extinguishing water run-off. For a holistic evaluation of firefighting methods, the tactical assessments and priorities of the fire service were also studied. In total seven medium-scale fire tests were carried out in a 13.5 m2 compartment with a ceiling height of 2.4 m, a ventilation opening of 0.54 m2 and an adjacent corridor. The fuel in the experiments consisted mainly of a sofa with mattresses according to specifications given in the "open space" test specified in the standard IMO Resolution 265 (84) and walls clad with OSB boards. One experiment was carried out with real furniture. The study focuses on indirect extinguishing (i.e., cooling of the fire gases) with four different extinguishing methods, which are: • Coldcut cobra cutting extinguisher and water, • Spray nozzle and water, • Spray nozzle and foam, • Fognail extinguishing spear and water. The extinguishing was started based on a temperature criterion of 350°C, 80 cm below the ceiling. The water consumption during extinguishing, the fire compartment temperature, as well as the particle and the gas concentration (CO, CO2, etc.), were measured during the experiments. Measuring devices for temperature, polycyclic aromatic hydrocarbons (PAHs) in particulate phase and volatile organic compounds (VOCs) were attached to a firefighter’s jacket to measure exposure. The firefighters stayed, during all experiments, for at least 1.5 minutes in the fire compartment to ensure a measurable PAH and VOC exposure. The experiments were furthermore documented with video recordings from several angles and infrared video of the fire compartment. After four of the trials, interviews with the fire service were conducted to evaluate the tactical assessments made during the firefighting effort. In the experiments, all extinguishing methods caused the temperature in the smoke layer to drop below 150°C within 2.5 minutes and the flaming fire was extinguished. The fire re-ignited in all experiments approx. 6 minutes after the start of the experiment, except for experiment F4, extinguishing with foam, where there was re-ignition after approx. 4 minutes. The experiments showed that the cutting extinguisher and Fognail have a good effect, even under "artificial" limitations in the experiments (duration and direction of the extinguishment). Both of these extinguishing methods used approximately the same amount of water. As the purchase costs for a Fognail are significantly less than for a cutting extinguisher, the Fognail has been found to be not only an efficient extinguishing method but also beneficial from a cost/benefit perspective. Purchasing costs are important for the fire service, especially for smaller fire services. Foam had the poorest cooling effect in the experiments and led to the fastest re-ignition. It was therefore concluded that foam is at high temperatures the least suited extinguishing method to reduce the temperature in the fire compartment. However, it is important that the use of foam is considered depending on the given fire scenario since the present study did not evaluate all properties and possible benefits of foam (such as the ability to cover flammable liquid). Furthermore, it can be assumed that foam can have a better effect when the temperature in the fire compartment is first lowered by using an external extinguishing method. The combination of foam and external extinguishing methods was not investigated in the present study. It is therefore recommended to evaluate this combination in future studies. To use an external extinguishing method (cutting extinguisher or Fognail) as an immediate measure in advance of internal firefighting gives the following advantages compared with smoke diving without the use of an external extinguishing method: • less soot and less explosive/toxic fire gases in the fire compartment, • better effect of the secondary internal extinguishing agent, • faster reduction of the temperature in the fire compartment, • less sauna effect (high humidity can cause heat to penetrate the clothes of the firefighters, which in turn can lead to injuries and that the smoke divers must retreat). The measurements during the experiments show that the use of cutting extinguishers or extinguishing spears can reduce exposure to the fire brigade with regard to heat and contact with particles. It was not possible to identify a clear trend for exposure to the carcinogens (PAH and VOC) measured at the firefighter’s jacket, by comparing the different extinguishing methods in the experiments. The experiments and interviews with the fire service further showed that the firefighter underestimated the negative ejector effect that ventilation openings into the fire compartment have. That is, placing a nozzle near an opening can lead to more oxygen being supplied to the fire which aggravates the situation. The video recordings from the experiments are published together with this report and will be a good learning tool for the fire service.
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