Before the man was hired, he did not disclose he suffered from bipolar disorder - either in an interview or a job application which required him to list any conditions that could affect his work.
Early in the morning after his first shift, the man called his supervisor in an "hysterical" state to say he could not go to work later that morning.
He later gave his supervisor a medical certificate from the Auckland Mental Health Crisis Team which indicated he was not fit to return to work for three days.
The company's operations manager proposed a meeting to discuss the issue, then sacked the man with a phone call and an email two days later.
The man argued before the ERA that he was under no obligation to disclose his illness under the Human Rights Act and had he done so, he would not have been hired.
He also argued the job application form breached the Privacy Act.
But the ERA has found the man's condition was relevant, given the job put him in sole charge of "a large factory using dangerous chemicals in the dead of night".
The company was completely unaware of his illness and was therefore unable to make an informed decision about how to protect him But the ERA also found his dismissal was unjustified, because the company did not wait to the end of his sick leave to raise the matter and failed to give him the opportunity to respond.
However, the ERA declined compensation, noting the man's failure to inform the company made him "entirely the architect of his own misfortunes".
Chen Palmer employment law expert Blair Scotland said there was a tension between an employee's right not be discriminated against and the employer's obligation to provide a safe working environment.
"Employers are held to a very, very high threshold to ensure that people are safe in the working environment, so much so that employers are expected to keep employees safe from themselves.
"So you're seeing a clash between those obligations, and obviously an obligation for an employee not to be discriminated against.
"It raises very difficult questions for someone suffering from a mental health condition. What do they do - do they disclose, and then face being discriminated against?
"It's a hard decision from both perspectives."
Mr Scotland said the decision turned on the nature of the role.
The company might not have had grounds to dismiss the man in a less dangerous role, like an office job, but he was in sole charge in a dangerous role.