Odourless, tasteless, and heavy - carbon monoxide is one of the greatest hazards when working in a confined space, according to a workplace safety consultant.
As a consultant for mining sites, Mackay Safety's Mick Storch guides companies in avoiding the risks associated with confined work spaces.
It was hard to tell when carbon monoxide was present, he said.
"You can't see it, you can't smell it.
"There's some things that can feel funny on your body, but if you're in an enclosed space, you don't know generally."
This was especially true for someone if the area was not their usual workspace.
Carbon monoxide poisoning can happen without the immediate symptoms being obvious, or they may be confused with those of fatigue or a common cold.
If symptoms show up - including tiredness, headaches, dizziness or nausea - it may be too late to reverse the effects of the poisoning.
When assessing the safety of confined working spaces, other risks included the presence of other noxious gases, Mr Storch said.
Plant-based material could also dispel oxygen as it broke down, making it difficult to breath.
Other risks of confined spaces were inundation, such as in grain silos, or lack of a viable exit in case of an emergency.
"It starts off with access and egress, which ultimately can affect the emergency response.
"If something does go wrong, it shouldn't take you long to get someone out of there."