"These failures led to unnecessary and unacceptable injuries to a worker."
He said the dangers of hydrogen sulphide gas were well-known in the tanning industry, and the worker was shifting containers when he was overcome by the gas.
"He fell to the ground, striking the back of his head on the floor.
"He regained consciousness, but he was disorientated, and he attempted to get back on to his forklift, and then he lost consciousness again and this time he fell forward, striking his face on the ground.
"He was noticed by another worker, who raised the alarm."
In a reference to a leak of hydrogen sulphide at Tasman Tanning in 2012, Mr Stewart said businesses had to learn from their mistakes and ensure changes were effective.
"When a business is held to account for breaches of the law, ensuring the breaches aren't repeated is a cornerstone of good health and safety practice. Failing to do so is a breach of workers' rights to a safe workplace."
A chemical spill at the tannery in November 2012 saw 21 people affected by hydrogen sulphide gas, with the two worst-affected being flown to Wellington Hospital in a critical condition. In October 2013, the company admitted safety failures in the Whanganui court and was fined for the breaches.