(Bloomberg) -- U.S. aviation safety officials are raising newwarnings about the dangers of carrying bulk shipments oflithium-based batteries on commercial flights.

The NationalTransportation Safety Board on Tuesday urged that batteryshipments be separated from other flammable materials on cargoplanes and that limits be placed on how many can be transported.Hours earlier, the Federal AviationAdministration sent a notice to airlines urging them to studythe fire and explosion risks of lithium shipments — linked tothree accidents — before they place the volatile power packsin cargo holds.

“FAA battery fire testing has highlighted the potential risk ofa catastrophic aircraft loss due to damage resulting from a lithiumbattery fire or explosion,” the FAA said in a press release.

The action is the latest to highlight the safety threat posed bythe power supplies for a growing list of products, from Apple Inc.iPhones to electric vehicles and power tools. FAA research showsrechargeable lithium-ion batteries can explode so violently thatthey could shear open an aircraft fuselage.

It also comes as legislation proposed last week to set FAApolicy for the next six years would continue a prohibition on newlithium restrictions in the U.S. that are stricter than thoseadopted by the United Nations’ aviation arm, the International Civil Aviation Organization.

Airline ban

While most passenger airlines last year banned bulk shipments oflithium rechargeable batteries, some U.S. and foreign airlinescontinue to carry them and there is no legal restriction.

Cargo companies such as United Parcel Service Inc. and FedExCorp. have not followed the passenger carriers in banning theshipments. Both companies are working on technology to limit thepotential for battery fires.

The Air Line PilotsAssociation, the largest flight-crew union in North America,separately on Tuesday called on Congress to give the FAA more powerto regulate lithium shipments.

“Lithium batteries pose a significant safety threat to airtransportation,” Mark Rogers, head of ALPA’s dangerous goodscommittee, said at a briefing. “It’s important that the U.S. notdelegate its responsibility as a sovereign nation to aninternational body. The U.S. should set the example and leadinternational efforts.”

Voluntary regulations

Because of language in a 2012 bill, FAA and the Pipeline and HazardousMaterials Safety Administration, which jointly regulate howhazardous materials may be carried on airline flights, have had toresort to voluntary recommendations instead of regulatory action inspite of growing evidence implicating the batteries.

Aircraft manufacturers Boeing Co. and Airbus Group SE warnedcarriers last year against carrying the batteries as cargo untilnew protections are developed. While it can’t impose the actionsitself, the FAA in October said it favored a ban on shipmentsaboard passenger flights until ne

w packaging can prevent fires and urged ICAO to take the sameposition.

An ICAO panel in October rejected such a ban. Another ICAOadvisory panel on Jan. 28 took the opposite position, sayingshipments should stop until new packaging is developed. The ICAOCouncil must decide the issue later this year.

Asiana crash

Three cargo aircraft accidents, two of them fatal, have beenlinked to lithium-based batteries that caught fire, according tothe NTSB and other accident investigation agencies.

The NTSB, which can only recommend regulatory changes, said itsinvestigation of a 2011 crash of an Asiana Airlines in waters offSouth Korea led it to conclude the risk of a fire from batterycargo warranted action. It urged the Pipeline and HazardousMaterials Safety Administration to impose restrictions on theplacement and volume of lithium battery cargo.

“The NTSB strongly believes the circumstances and findings inthe Asiana Flight 991 accident show the need for new cargosegregation and loading density requirements,” the NTSB said in anews release.

Delta, United

While many large passenger carriers, including UnitedContinental Holdings Inc. and Delta Air Lines Inc., said last yearthey won’t ship the power packs as cargo until new safety measuresare developed, such shipments are legal and some carriers continueto handle them. About 26 million people a year fly to and from theU.S. on foreign carriers that allow lithium shipments, according tothe FAA.

The FAA’s advisory Tuesday doesn’t apply to batteries containeddevices carried by passengers and crew members.

The agency said it “strongly recommends” that passenger andcargo airlines review their battery shipments as more evidenceemerges about the threat. Not only will the power units explode,but they also can emit smoke and gases that will spread to the restof the aircraft, the FAA said in the alert.

“The number of cells necessary to produce this condition issmall and can occur with just a few packages,” the agency said inthe alert.

Airlines should review the types of batteries they carry, thereliability of the companies shipping them and their employeetraining, according to the agency.

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