Odourless, tasteless, and heavy - carbon monoxide is one of the greatest hazards when working in a confined space, according to a workplace safety consultant.
The gas' weight makes it sink to the bottom of an enclosed area, so that anyone working there may collapse if they bend down, Mackay Safety consultant Mick Storch said.
"Essentially, because it's heavier, it displaces the oxygen."
As a consultant for mining sites, he 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.
When assessing the safety of confined working spaces, other risks included lack of oxygen, or presence of other noxious gases.
A worker had died working in a pontoon off Queensland due to rust inside.
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."