There is growing pressure in the aviation industry to ban the shipment of lithium-ion batteries, like the consignment aboard Flight MH370, on all passenger-carrying airplanes. Well before the Malaysian Boeing 777 disappeared, there was rising concern that bulk packages of the batteries posed a safety hazard.

Last fall, the Federal Aviation Administration carried out a series of tests at its Atlantic City technical center that simulated the consequences of the overheating of batteries carried in the cargo hold of an airliner. The tests took place in a 1960s vintage Boeing 727 airframe. They involved different sizes and combinations of the kind of lithium-ion batteries that are regularly shipped by manufacturers for use in electronics from cellphones to laptops.

In several of the tests, smoke and fumes from deliberately induced overheating of lithium-ion batteries reached the cockpit in less than 10 minutes. Had this happened at cruising altitude in the course of an actual flight instead of during a ground test, the pilots would have had to don oxygen masks, as would the passengers. Even then, survival would be doubtful. Halon 1301, the standard fire suppressant employed on airliners, has no effect on lithium-ion battery fires. Another test had a more violent result: An explosion blew open the door between the cabin and the cockpit.

The FAA tests were reviewed by experts from the International Civil Aviation Organization (the Montreal-based United Nations agency that oversees international air travel), the European Safety Agency, and others from the airplane and battery industries.

There are several problems involved in assessing the value of such tests. The most challenging one is that so little is still understood about what can cause lithium-ion batteries to overheat and induce what is called a “thermal runaway,” a virtual meltdown of the battery and its casing.

In the FAA tests, the batteries were subjected either to “cooking”—subjecting them to very high temperatures—or given an excessive charge that caused them to heat up to 190 degrees Celsius to trigger a thermal runaway. Of course, a deliberately forced failure like these leaves no doubt about how the process was instigated. The trouble is that in a real battery emergency it can be very difficult to establish how it was initiated. Certainly the most costly and dramatic battery failure so far, the one that led to the grounding of the entire Boeing 787 Dreamliner fleet, demonstrates this difficulty very well.

This occurred early in 2013 when there was a thermal runaway in the lithium-ion batteries of a Japan Airlines 787 parked at the gate at Boston Logan Airport. Following this emergency, hundreds of hours of testing were carried out by the National Transportation Safety Board, Boeing, and a so-called “brain farm” of specialists. Even then, it proved impossible to replicate what had happened in Boston, where the thermal runaway had begun in one battery cell and then spread to others.

In March 2013, announcing changes made to the installation of the batteries in the 787—changes that ended the grounding of the fleet—Boeing said: “The battery case will sit in a new enclosure made of stainless steel. This enclosure will isolate the battery from the rest of the equipment in the electronic bays. It will also ensure that there can be no fire inside the enclosure, thus adding another layer of protection to the battery system. The enclosure features a direct vent to carry battery vapors outside the airplane.”

In other words, the question was not whether the batteries could fail again. This redesign was based on the assumption that they might, and the fix was to make sure that if they did the safety of the airplane would not be compromised.

A month after that announcement, unaccustomed daylight was forced upon the lithium-ion battery industry. Deborah Hersman, the head of the National Transportation Safety Board, convened a two-day public hearing designed to trace the history of lithium-ion batteries as they were developed for use in airplanes. (Before Boeing chose the technology for the 787, nobody had required such powerful industrial-scale battery packs—generating 1.5 megawatts, enough to provide electricity for 400 houses.)

Representatives of the battery manufacturers were clearly uncomfortable. Some said that they could not answer questions because intellectual property rights were involved. Overall, it became evident that nobody was ready to say that the technology was either mature or 100 percent reliable—or that the behavior of the batteries was totally understood.

One witness said that during the development of the batteries “failures occur in ways that the designer never envisioned.” Hersman herself asked if they could define failure, but nobody seemed able to because it occurred in so many different ways. One witness volunteered: “You’d better burn some batteries to know what they look like.”

A picture emerged of a technology that was just too appealing to early adopters, like Boeing, to be resisted because lithium-ion batteries deliver far more power for their weight than any other kind of battery, and weight is the enemy in an airplane. (Airbus, having watched Boeing’s travails, dropped the idea of using lithium-ion batteries in its rival, the A350).

In fact, the development of the lithium-ion technology had been driven so hard and so fast that it had outpaced the ability of the FAA regulators to know at what point they could freeze the safety standards they were preparing in order to certify that the 787 was safe to fly.

I interviewed Hersman some weeks after those hearings. I suggested to her that there still seemed to be no consensus on what those safety standards should be.

There was, she admitted, a dilemma: “How much development needs to take place before you begin to set standards?”

And she added: “What we heard was that they were using testing standards that were the industry standards, then they also said they were using testing standards that were state of the art. There is a disconnect between those two things. ‘State of the art’ to me speaks to real cutting-edge testing standards, but ‘industry standards’ take years to get completed. When they were completed [in the case of the 787], they weren’t retroactively applied to the aircraft being certified.”

To be sure, there is a big difference between a 40-pound industrial-strength battery pack designed to power the systems of a large airplane like the 787 and a consignment of lithium-ion batteries destined for use in consumer electronics devices like laptops and cellphones. What matters in the case of a shipment like the one aboard Flight MH370 is how they are packed—the kind of separation there is between each battery and the total mass.

Last week’s release of the cargo manifest by the Malaysians has not helped to give us a clearer picture. Far from it, in fact. Originally, the Malaysians said that the battery consignment weighed 440 pounds. However, the manifest shows a far larger consignment weighing 5,400 pounds in total, alongside a warning that “a flammable hazard exists.” It has now emerged that the batteries were but one part of a consolidated package that also included radio accessories and chargers. Malaysian Airlines still insists that the lithium-ion batteries in this package weighed only 440 pounds. Even if half of that weight of 5,400 pounds consisted of packaging, this shipment concentrated far more battery energy—hence potential firepower—than in the power pack of a 787. The cargo manifest released last week said that the packaging of the batteries was “in compliance” with the international regulations for the shipment of hazardous materials. That may be so. But what investigators need to know in the case of Flight MH370 is what happened when such an unusually large and fragile consignment is loaded—how well was this supervised, was there any damage during loading, and how secure was its placement among the other cargo?

Total mass becomes significant because of the propensity of a thermal runaway to spread rapidly. In the case of the 787 incident in Boston, the reaction spread from one cell to another until it reached a critical mass that basically fried the whole unit. If the same thing occurred in a large bulk package of consumer-sized batteries, with a runaway increase in heat, it could soon replicate the behavior of the 787’s batteries.

How can this saga of the lithium-ion batteries be tied to the fate of Flight 370?

The Boeing 777 flew for as long as seven hours with all its essential systems working. Its life ended when it ran out of fuel. Thus comes the Zombie Flight Scenario: Something incapacitated all humans aboard, the crew and the passengers, and yet left the airplane able to be continue to be flown by its flight management computers.

The Zombie Theory is one of the few explanations that seems to fit this greatest of all aviation mysteries.

Nonetheless it can be challenged on several grounds. If the batteries in the cargo hold did overheat and a chain reaction led to fire – a fire that the 777’s fire suppression systems could not have contained – that fire would not just have generated smoke but enormous heat that would have seriously damaged the airplane’s structure and made it impossible for the flight to continue for so long.

True, but we know that what happens to these batteries when they overheat is extremely complex. At cruise altitude of 36,000 feet, the behavior of a battery runaway would not be the same as it was on the ground in Boston where there was an endless supply of oxygen to sustain a fire – smoke aboard an airplane at cruise triggers the deployment of oxygen masks, and the oxygen supply in the airplane is swiftly depleted.

A tenable explanation is that some kind of meltdown in the battery consignment generated fumes consisting of vaporized electrolyte—at the NTSB hearing a witness described fumes that began as white smoke, then turned gray and finally black—but, once starved of oxygen, the reaction ceased, without degrading the 777’s airframe or systems.

In other words, the humanly inhabited part of the 777 became like a gas chamber in which the lethal fumes did their work and then dissipated, leaving just the machine intact.

Another serious challenge to the Zombie Theory is the absence of any Mayday call from the pilots. Even if their oxygen masks had deployed, there is a microphone in the masks to enable them to send a distress call.

This is, indeed, a strong point. However, it is possible that the pilots did make several Mayday calls but these went unheard both by other airplanes and ground controllers. This possibility gained some weight last week when the Malaysian preliminary report revealed prolonged confusion among air traffic controllers in Thailand, Cambodia, Vietnam, and Malaysia attempting to locate Flight 370. Given the record of multiple derelictions during the critical period following the 777’s sudden change of course, it’s quite possible that nobody was listening to their cry for help.

A final challenge to the Zombie Theory is the fact that the ACARS system, which automatically and periodically transmits data about the 777’s condition, stopped transmitting, and also that the airplane’s transponder, constantly reporting its position, turned off—the implication being of malign human intervention. However, both these things could be explained by relatively limited damage to electrical circuits.

Whether or not the batteries were involved in the fate of the Malaysian 777, their record so far suggests that they pose an unacceptable risk in the cargo holds of passenger flights. To say that a consignment is “in compliance” with packing regulations is a mere fig leaf. The cargo manifest for Flight 370 lists the shipper as a company called NNR Global Logistics, but a spokesman for Malaysian Airlines said he could not name the manufacturer. It’s vital for investigators to be able to follow the whole chain: What kind of batteries were being shipped, what was their power, how were they packed—and, critically, what is the manufacturer’s record of quality control?

The dramatic tests by the FAA were part of a study being carried out for the ICAO so that industry leaders can consider new regulations for the transport of lithium-ion batteries in all sizes and forms. It is in the nature of both the ICAO and the industry (a combination of the sclerotic and the evasive) to hesitate before issuing something as draconian as a total ban on carrying the batteries on passenger flights. I am told that the options are: a total ban on passenger flights, with shipments confined to cargo-only carriers; no shipments by air at all; or none of the above—and, instead, limits on the quantity and type of batteries allowed in the cargo hold.

Given the ICAO’s record, I’m not holding my breath.

Despite some reporting to the contrary, there is no ban on the bulk shipment of lithium-ion batteries in cargo on passenger flights in the United States. It turns out that the regulations covering all shipments of these batteries were drawn up and promulgated by the relatively little-known Pipeline and Hazardous Materials Safety Administration, part of the Department of Transportation. Those regulations that apply to aviation shipments are enforced by the FAA, and relate to the standards for packing and loading.

One airline that has already banned shipments on its passenger flights is Cathay Pacific. Richard Howell, the airline’s head of safety, told the aviation data-gathering body, IHC Janes, that the batteries posed “a very real risk and this is getting bigger and bigger.”

Indeed, it is Asian carriers like Cathay Pacific (and Malaysian Airlines) that have major international routes that are most likely to be used for lithium-ion battery shipments. Manufacturers in China are the source of many consignments, and, as an industry source who did not wish to be identified told me, “Nobody really knows how the Chinese devise and enforce their safety regulations.”

Back in the U.S., the FAA is much more specific about what passengers are allowed to take on a flight. The batteries in cellphones, cameras, and laptops are not restricted and even larger batteries used in professional audio-visual equipment are allowed. However, spare lithium-ion batteries of all sizes are considered too dangerous for the cargo bay and must be in carry-on baggage and not in checked bags.