Two men are in a serious but stable condition at Wellington Hospital after toxic gas filled Tasman Tanning's Tod St plant in Castlecliff on Friday.
Another 21 people exposed to the tanning gas were taken to Wanganui Hospital where they were treated and discharged that night. Fire Service Assistant Area Commander Manawatu Rodger Calder said hydrogen sulfide was used in the tanning process to remove hair from animal hides, and when it was mixed with another chemical a gas was produced.
Mr Calder said six Whanganui firefighting staff donned level-4 protective suits.
The suits completely encapsulated and sealed the body and the men used breathing apparatus.
It was a dangerous environment for the men to work in because of the potential for an explosion due to the low explosive characteristic of the gas, Mr Calder said.
The firefighters had to shut down a machine to stop the gas being produced, then it had taken a couple of hours to clear the gas out of the building.
Once the building was safe at 9.30pm, firefighters had handed the site over to the Ministry of Business, Innovation and Employment (MBIE - formerly the Department of Labour).
The area of the plant where the gas escaped had been sealed off and today MBIE inspectors were to continue with their investigations.
Vivek Bangia, co-owner of a grocery store across the road, told the Chronicle that "all of a sudden many staff rushed out of the building" around 5pm on Friday.
He said his store staff had smelt the gas for up to 10 minutes and then it had dispersed quickly in the wind.
"We worry about them [tannery staff] as we have come to know them over the years.
"They have become like family."