Wildfires are a major problem both locally, regionally and globally. They destroy large values, emit large quantities of carbon into the atmosphere and are very resource intensive to fight. Smoldering fires can continue under the ground surface long after the flaming fire above ground is put out. Smoldering fires burn much slower than the flaming fires, but in turn they are harder to discover and require different means to fight.

Peat fire is one type of smoldering fire that can be found in wildfires. It is a smoldering fire that occur in peatlands exposed to drought. The fire slowly eats its way through the peat and can go deep into the ground. Difficulty locating them and getting enough water into the deeper peat layers makes them difficult to extinguish.

Today, fognails are often used to extinguish smoldering fires in the ground. The cutting extinguisher is another tool that has been used to fight smoldering fires in the ground in some cases. This bachelor thesis aims to provide a better understanding of the function and efficiency of the two tools in extinguishing peat fires. To do this, two tests have been carried out on the fire department’s training field in Luleå, one with a fognail and one with a cutting extinguisher. A test stand was constructed with an internal cross-sectional area of ​​80×80 cm and a height of 1.1 m. It was then filled with peat which was lightly packed until the peat layer was 1 m thick. What was investigated was the tools’ penetration time for the water to reach 1 m down into the peat and the size of the water spread over the cross-sectional area at the depth of 1 m.

Both tools had similar flows (56 l/min for the cutter extinguisher and 58 l/min for the fognail) so the differences arose in how that water was used, not the amount of water.

The cutting extinguisher broke through in about 1 second and formed an exit hole of about 1 dm² with additional wetness of a few centimeters around for a total wet area of ​​about 2 dm². The test was terminated after 30 seconds when no change could be seen in the size of the output hole or the wet area from after the first few seconds. The water sprayed right through the peat.

The water from the fognail got through after 26 seconds and the wet area grew continuously. No exit hole was formed in this case. When the fognail was turned off after 1 minute and 45 seconds, about 32 dm² had become wet, which corresponds to about half the cross-sectional area of the test stand. However, spreading continued despite the fognail being turned off and almost the entire cross-sectional area was wet after a few more minutes.

The cutting extinguisher had a very fast penetration time, but as a result it sprayed a lot of water right through the peat without wetting a large area or volume. The fognail had a much longer penetration time, but in return, the water was not shot straight through the peat, but spread out and wet a larger surface.

Both tools have their advantages and disadvantages. Which tool is the best depends a lot on the situation. The cutting extinguisher has, among other things, a faster penetration time and allows for more rapid interventions, while the fog nail covers a larger area per attack point and is easier and safer to handle.