The fire had been started by an explosion. Most likely it was a cleaning machine that had exploded.
Mikael Stenmark, the main safety representative at Northvolt, has previously explained that the cleaning machine is used to vacuum up debris and remnants from production.
Mikael Stenmark, huvudskyddsombud på Northvolt, har tidigare förklarat att renhållningsmaskinen används för att suga upp skräp och rester från produktionen.
– It stands above the production space and is like a large central vacuum cleaner. The filter needs to be changed regularly. A smaller vacuum cleaner is used to clean up material that accumulates during the filter change. Somewhere in this process, an explosion occurred, resulting in a big fire, he told Norran last Monday.
According to witnesses interviewed by the police, there was a loud bang. One person is reported to have described the blast to police as feeling like an earthquake.
A man in his mid-20s was taken to hospital with serious burns after the explosion. It was decided the same evening to transfer the man to Uppsala University Hospital. According to the latest information available, the man is still being treated for life-threatening injuries.
It is unclear what caused the explosion, and several investigations have been launched following the fire. Arbetsmiljöverket, the Swedish Work Environment Authority, is involved, and the police have opened a preliminary investigation into a possible offence of causing bodily harm.
This week the police have been at the site to carry out a technical investigation. After the investigation, prosecutor Christer B. Jarlås, who is leading the investigation, announced that material from the site would be analysed.
The police also visited Northvolt this week together with Arbetsmiljöverket.
In addition to the authorities' investigation, Northvolt has also launched its own investigation. Sanna Bäckström, a communicator at Northvolt Ett, says that the company is currently "working on certain theories" about what might have caused the explosion.
– But we still do not know what the cause is, says Sanna Bäckström.
Both "internal and external experts" are working on the investigation at Northvolt, she reports. According to Bäckström, the experts have, among other things, examined and documented the site of the explosion. Samples have also been taken.
– We want to understand all the parts. What could the different materials at the site contain that could explain the explosion? That's what we want to find out.
Chief safety officer Mikael Stenmark has previously told Norran that the location of the cleaning machine was not classified as a potentially explosive environment.
– I am surprised that an explosion has happened. It should not be possible, it should not happen, he said.
Other parts of the building contain similar cleaning machines to the one where the explosion occurred. In the aftermath of the accident, workers have expressed concerns about the replacement of filters on the machines. As a result, work has been suspended in several areas.
Bäckström told Norran earlier:
– We will not start up any machines until we have carried out the necessary checks and risk assessments to ensure that we can start up safely.
Northvolt's accident report to Arbetsmiljöverket also states that the production unit stopped in connection with the explosion "will be shut down until the investigation is completed".
When Norran spoke to Sanna Bäckström on Friday, she said that the investigation could take a few weeks. She also says that Northvolt is carrying out an "evaluation" and "risk assessment" after the explosion. However, she did confirm whether work at the sites where similar cleaning machines are located will be stopped until the cause of the explosion has been fully investigated.
– We have shut down for safety reasons and are working on a risk assessment and evaluation. We will of course continue to assess the affected areas and work to identify risks.
As a result of the fire, the sprinkler system was activated in part of the building. This week, Northvolt has been working to remove the water.
– The water has been drained, said Bäckström.
She says it is unclear at the moment whether there was any water damage to the building.
– We are investigating.
Northvolt employees have had the opportunity to receive counselling during the week.
– It is clear that people are worried after such an incident. We all deal with things in different ways and it is important to talk about our feelings, she says.