Testing ofthe sauna heater involved in the Hakunila fire continues

Fig­ure 1. The fire started in­side a first-floor flat in Haku­nila. (Im­age: SIAF)

Temperature measurements taken from behind the sauna heater

An inspection of the electric sauna heater revealed that the stone container had begun to bulge due to the stones condensing at high temperatures. Air circulation between the stone container, the outer walls of the heater and the mounting bracket had become partially obstructed. SIAF’s investigators ran a series of tests that involved mounting the heater on a plywood wall as per the standard procedure for testing sauna heaters. The heater was fitted with a new control panel, heating elements and wiring. Despite the structural deformations, temperatures measured from the wall behind the heater were still comfortably below the safe limits specified for sauna heaters.

Fig­ure 2. Heat stain­ing on the wall where the sauna heater was mounted. (Im­age: SIAF)

More testing to follow

SIAF’s investigators found a sauna that corresponds to the one where the fire occurred, and observed staining and slight charring on the panelled wall above the sauna heater. A decision was therefore made to base subsequent tests on a panelled wall and focus on measuring temperatures from the wall above the heater. The flammability of the panels will also be analysed. The goal is to establish the ignition mechanism in circumstances that are similar to the incident, where there probably was no clothing or other foreign materials in the vicinity of the sauna heater. The heater had been mounted directly on the panelled wall using a wall bracket designed for the model in question.

Fig­ure 3. The wall of a cor­re­spond­ing sauna, with smoke stain­ing and even some char­ring vis­i­ble in the area be­hind the heater. The ver­ti­cal struts help to keep the wall in one piece. (Im­age: SIAF)

No malfunctions detected

The investigators had previously established that the thermostat, timer and heating elements of the sauna heater functioned as intended. There were therefore no technical faults in the heater, and it was switched on at the time of the incident. The thermostat was set to almost the maximum temperature. Based on the timer position and electricity consumption data, the timer had probably been pre-set at some point during the evening. According to the father, no one had been in the sauna after his return home after 8 pm. The door to the sauna was closed, and the sauna heater having been used to dry laundry is not a logical explanation in the circumstances. Everyone was presumably asleep when the heater switched on.

The family had lived in the flat for approximately two months. According to the father, the family had used the sauna once. Electricity consumption data support the father’s statements.

Findings of the investigation to be released in the summer

A few more months are still needed to complete the investigation, but SIAF will keep the public up to date on the progress of the investigation and release more information as and when new discoveries are made. The current advice for everyone who has a sauna is to have their sauna heater serviced at regular intervals.

‘The sauna heater stones should ideally be replaced or at least rearranged loosely at least once a year to ensure that air can circulate through the heater and prevent overheating. Regular visual inspections of the heater and the area around the heater are also a good idea’, says Investigator-in-Charge Kai Valonen.

Edit 19.9.2024: The investigation is still ongoing and further investigations of the sauna heater are continuing. In particular, the mechanism of ignition still needs time to be determined. The new estimated completion date for the investigation is the end of 2024. 

Further information:

Mr. Timo Naskali, Investigator-in-Charge, tel. +358 (0)29 515 0740

Ms. Tiina Bieber, Head of Communications, tel. +358 (0)29 515 0714