The contractor NCC has informed SSAB that three office employees at the workplace have reported symptoms. NCC reported the incident to the Swedish Work Environment Authority on Monday.
NCC will move its office staff to other premises.
Several other people have been affected in the past. They have worked on construction machinery in various locations in the area.
On April 3, SSAB stopped work at the construction site after around 20 people fell ill, seven of whom received treatment. Work is still suspended.
Among the symptoms that have been observed are nausea, headaches and irritated airways.
The day before work stopped, test results showed that elevated levels of toxic gas had been found in the cabins of the machines.
SSAB now says that gas measurements in the ambient air at all temporary office premises on the construction site, including SSAB's own, have not shown elevated levels.
It was therefore concluded that it is unlikely that corresponding gases would be present at significant concentrations inside the buildings.
"We cannot currently say with certainty what the root cause of the reported cases of illness is. We are continuing to take samples to confirm or rule out possible causes," writes SSAB.
