An expert in toxic gas believes an ammonia leak at a Northland factory could have easily been fatal.
Emergency services were called to the AFFCO processing plant in Northland's Moerewa on Friday, prompting evacuations of nearby houses.
No one was hurt in the leak.
Ammonia is a strong smelling colourless gas, often used for cleaning. It can be extremely dangerous if inhaled, irritating the skin, eyes, nose, throat and lungs.
Padraic Durham from the Ammonia Safety Association, says working with the gas is risky.
"If you look at statistics, we haven't really injured anyone for quite same time. The last person who died in this country of ammonia was at that same facility. We're at that stage of waiting for the next casualty."
The leak was contained to the control room.
"It's highly corrosive at dangerous levels - we're talking 300 parts per million upwards," says Mr Durham.
"At lower levels it's not considered so dangerous, but it's pretty uncomfortable for people who aren't really assimilated with it."
AFFCO Moerewa processes calves from slaughter through to further processing, according to the company's website. It is the biggest employer in the region.