The U.S. National Transportation Safety Board (NTSB) says that rail tank cars carrying oil or ethanol need to be retrofitted or replaced to make them more fire-resistant. The NTSB says that several explosive accidents in recent months have revealed the shortcomings of voluntary industry standards.

The NTSB issued a series of recommendations that call for an alternative system of protections that are able to withstand fire better than the bare steel construction now widely used. It says a decade-long retrofit timeline suggested by the tank car industry is too long to wait.

“The longer we wait, the more we expose the public to the problems of these cars that aren't especially robust," NTSB Chairman Christopher Hart was quoted as saying by the Associated Press.

The safety board proposed equipping flammable liquids cars with ceramic “thermal blankets" that surround the tank and shield it from intense heat in case a nearby car catches fire. Those blankets are used in rail cars that transport liquefied petroleum gas.

The safety board also recommended relief valves that can prevent pressure from building inside tank cars as they heat up from nearby fires.

The industry voluntarily adopted rules in 2011 requiring sturdier tanks for hauling flammable liquids.

“Every tank car moving crude oil today should be phased out or built to a higher standard," the Association of American Railroads says in response to the NTSB announcement.

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