Petroleum exploitation companies operate a fleet of Ice Breaking Emergency Evacuation Vessels (IBEEV) on the Caspian Sea, to service the extensive oil fields there.The vessels are designed to evacuate up to 338 individuals per trip. They are designed to function using compressed air to power their engines, if they are passing through pools of burning oil, or oxygen poor environments—carrying enough compressed air to function for 50 minutes. Every evacuee is issued a rebreather, for passing through anoxic environments, if the airtight evacuation capsules are compromised. The vessels are insulated so passengers and crew can survive transiting through pools of burning oil. Since the Caspian freezes during winter the vessels are designed to break up to 0.6 metres (2.0 ft) of ice.