OLYMPIA's coal bunkers can be observed in a variety of locations, but a good place to see one is adjacent to the boiler, but way of the small hatch.
Coal supply aboard a warship of the OLYMPIA's era was an item of extreme importance. The coal was consumed by the boilers at different rates, depending on the intended speed of the ship and the quality of the coal. For instance, at the OLYMPIA's normal cruising speed, she would use about 300 pounds of coal every five minutes. When traveling at battle or flank speed, she would use about eight times as much, or 2,400 pounds of coal every five minutes.
The location of coal within the ship would effect the ship's "trim" (i.e., if all of the bunkers on one side of the ship were emptied, she would lean drastically to one side), so the use of coal was monitored to keep the ship in trim. Also, not all of the coal that was received aboard the ship was of equal quality. If some particularly good coal was received, it may be stored in a bunker closest to the boilers for immediate use in battle or in an emergency. The location of the nearest coal supply had to be kept in mind, so that the vessel could make port to resupply before it ran low.
Working within the bunkers was a terrible job. Since the coal bunkers could be long, men had to shovel the coal around in the bunkers, so that the bunkers could be filled evenly, and in all corners. When the coal was being used, a shovel relay would be set up in the bunkers, so that the coal in the bunker could be used evenly, and a ready supply kept at the entrance to the bunker. From this point it was shoveled in manageable quantities into the boiler rooms. The bunkers were hot, often humid, and the air thick with coal dust.
Coal bunkers were subject to fires from spontaneous combustion. This was caused by the newly exposed surfaces of coal absorbing moisture and giving off heat. The heat could build up until the coal actually began to burn. The OLYMPIA had several coal bunker fires in her history. The only way to put out a coal bunker fire was to dig down and expose the burning portions and flood it with water...or use the burning coal in a boiler! A fire in a coal bunker fire is believed by some to be the cause of the explosion aboard the Battleship MAINE.