You see an explosive barrel.
This dwarven barrel is highly explosive and instable. It's literally only a matter of time until it goes off.
Location
Notes
When used at the correct location, it will explode (KABOOM!) after 5 seconds. When activated, it looks like this:
They are part of the Dangerous Depths Quest - Explosive Growth.
An Explosive Barrel exploding. The damage taken can be reduced by wearing Fire protection equipment.
See also: Explosive Barrel
History
It also used to deal 1000 Fire Damage when exploding, but this was removed in the end of 2018, but the change was not announced.