Underwater Wakulla
Fires in Diving
Kona Divers on the Big Island of Hawaii, just down the street by an hour, had a very serious fire on Friday. Fortunately, the fire was contained to the upstairs of the store, as they had just installed an Oxygen blending facility downstairs. The oxygen cylinders would have been of great concern had the fire reached the fill station. Fire in diving is always a big concern. We know about the challenge with a house fire melting aluminum cylinder not fully filled. They explode before the burst disk pressure is reached, sending shrapnel throughout the building. Kona Divers had plenty of them downstairs too.
For starters, oxygen used to make Nitrox, or while filling oxygen cylinders, creates an elevated risk of fire in a number of ways. If the cylinder contains hydrocarbons left over from a compressor using non oxygen comparable lubricants, a fire can combust with the heat of compression and a spark. Partial pressure filling tanks to make Nitrox, results from first pumping 100% oxygen into the cylinder before topping it off with air. Worst would be when 100% oxygen is pumped directly into a cylinder, not rendered oxygen clean with a nontoxic, degreasing agent. A Nitrox facility in the Florida Keys exploded when one of their flasks, being pumped with oxygen, sent the entire stack flying everywhere, including across the canal and into yachts parked across the canal.
When hoses or fill valves are not made oxygen clean, they too can burn under the right conditions. When the fire happens in the hose, we call it flashing. Take a Q-tip and push it into the hose and see if you can pull out a black residue. All fill whips should be flushed with a degreaser like Crystal Green every few years just to be sure.
Many years ago, an oxygen cylinder was dropped while being filled, resulting in a curse, a clank noise, a whoosh noise and a bang explosion, killing the fill station operator and setting the store on fire. Customers were also injured. The company never fully recovered. Handling pure oxygen is risky. Cylinder pressures above 500 psi elevate the risk of a fire with higher pressure. The industry recommends not filling cylinders over 3000 psi, very slowly (not faster that 100 psi per minute) and cautiously. Containment is highly recommended.
Rebreathers are subject to the risk of fires. One of the cylinders on a rebreather is full of pure oxygen. That gas must flow through a regulator before being fed into the breathing loop. Fires have occurred when a simple interlocking o-ring was replaced, accidentally lubricated with silicone (very fire-prone in the presence of pure oxygen). The damage included melting the regulator, the tank valve and burns to the owner. A similar fire occurred when the tank valve was serviced by a technician unfamiliar with oxygen safety who lubricated it with silicone grease. The fill station operator had a similar explosive fire experience. On a boat in the Red Sea, a group of rebreather divers were assembling their rigs when a diver forgot to open his oxygen cylinder before putting the rig on his back. When he remembered, he reached back and flipped it on quickly. The regulator burst into flames, prompting the diver to swing the rig off his back and on to the deck of this wooded boat. Everyone then jumped overboard, all but one person leaving their rigs on the boat. The sea was flat calm, so everyone watched their expensive rebreathers burn up as rescue boats converged. Someone got a great picture.
Every year someone burns a compressor up explosively while blending Nitrox. We did once, when the monitoring oxygen sensor failed and resulted in too high an oxygen content for the design of the compressor. The resulting bang exploded the safety pressure relief devices, turned the oxygen compatible oil in the crank case black, and scared all of us! Fortunately no further injury or damage happened, but we never used that compressor again. Fires in diving are ever present!
From the Underwater Wakulla archives.