Photo: RNZ / Nate McKinnon
The incident happened inside a self-contained chemical processing container in Bromley, Christchurch.
The organisation behind the incident was Rolleston-based Pest Control Research (PCR), which makes pest control products, including 1080 baits.
WorkSafe says from 2018 to 2019, the group was experiencing supply issues with 1080 (scientifically known as sodium fluoroacetate) - and set up a project to manufacture its own supply of the poison.
The project was code named the Home Brew Project / Project X .
WorkSafe head of specialist interventions Dr Catherine Gardner said: Health and safety requirements were not met from the very start of this project and cumulatively design, fabrication and process errors ultimately resulted in workers being exposed to highly toxic vapour from a failure in the manufacturing process and in PCR s overall safety management systems.