When I tell people I work on hydrogen fuel, they immediately say something very wrong like, “Are you worried about a mushroom cloud over your lab?” — Mushroom clouds are from a nuclear bomb detonation, and I don’t plan on starting thermonuclear fusion anytime soon in my lab, and if I did, it might save the planet. The other statement I usually get is, “Wow, don’t want another Hindenberg!” Again, very wrong. Several detailed studies from NASA and others have shown that the Hindenburg disaster was not caused by hydrogen. The Hindenburg’s sister ship, the Graf Zeppelin flew more than a million miles for nearly a decade on hydrogen before being grounded after the Hindenberg disaster. Go in and read the studies for yourself. The Hindenberg cut several corners the Graf Zeppelin did not, and you can’t expect the hydrogen to blow-out a diesel fire. The final one I sometimes get is, “Oh, the Challenger Shuttle!” again very wrong, Challenger was caused by the failure of a solid-oxide rocket booster o-ring.
So really, if I’ve just debunked the three most common misconceptions about hydrogen ‘incidents’ in a single paragraph, how dangerous is hydrogen fuel?
“Tests were devised in which tanks containing liquid hydrogen under pressure were ruptured. In many cases, the hydrogen quickly escaped without ignition. The experimenters then provided a rocket squib (a small powder charge) to ignite the escaping hydrogen. The resulting fireball quickly dissipated because of the rapid flame speed of hydrogen and its low density. Containers of hydrogen and gasoline were placed side by side and ruptured. When the hydrogen can was ruptured and ignited, the flame quickly dissipated, but when the same thing was done with gasoline, the gasoline and flame stayed near the container and did much more damage. The gasoline fire was an order of magnitude more severe than the hydrogen fire. The experimenters tried to induce hydrogen to explode, with limited success. In 61 attempts, only two explosions occurred and in both, they had to mix oxygen with the hydrogen. Their largest explosion was produced by mixing a half liter of liquid oxygen with a similar volume of liquid hydrogen. Johnson and Rich were convinced that, with proper care, liquid hydrogen could be handled quite safely and was a practical fuel — a conclusion that was amply verified by the space program in the 1960s. At the time, however, Johnson and Rich filmed their fire and explosion experiments to convince doubters.” https://history.nasa.gov/SP-4404/ch8-6.htm
That was during the 1950’s “Project Suntan” days with Kelly Johnson as project lead (yes that fabled Johnson that started Skunkworks and led the design of the SR-71 Blackbird, among others). For whatever reason, perhaps to remove all doubt, the Air Force Research Labs (AFRL) decided to reproduce Kelly’s experiment in the early 1980’s at Wright Patterson Air Force Base. This experiment involved shooting each container with .50 caliber incindiary rounds and simulating lightning strikes. This time hydrogen (on the top) is being compared with kerosene (on the bottom, aviation fuel or JP-1).
This confirmed Kelly’s findings that the hydrogen fire ball dissipated quickly, providing less damage to the structure in every case versus the JP-1 test. The lightning test was inconclusive due to the container being obliterated in each case. The end result: hydrogen is safer than aviation fuel for aerospace applications involving an incendiary round penetrating the fuel tank. if you want more info on hydrogen safety in aerospace applications, NASA has loads of documentation on the history on-line, you can also check out Daniel Brewer’s book “Hydrogen Aircraft Technology.”
But we’ve talked about blimps and planes so far. How does this translate to conventional automotive vehicles? The National Highway Transportation and Safety Administration has a comprehensive report on the hydrogen safety studies for vehicles. The report reviews international research as well as US research. The report identifies one direct comparison between hydrogen and conventional gasoline vehicles conducted by the US Department of Energy. Here’s a few pictures from the study, try and guess which car is fueled with H2 and which car with gasoline:
Very similar to the aerospace studies, when a hydrogen storage tank ruptures and the leak ignites, a hydrogen flame burns out, and up and away from the structure, very quickly. One number that I remember from an introductory hydrogen technology class is that hydrogen diffuses away at 40 miles/hour. Hydrogen literally is so fast that it has escape velocity and will eventually dissipate into space and the upper atmosphere. This is one of the inherent safety features of hydrogen — it doesn’t stick around long outside of a container. So as long as you don’t capture hydrogen beneath a structure where it can accumulate in dangerous quantities, you’re fine. Sadly, this excludes most research labs and garages where hydrogen sensors and ventilation must be carefully considered. Thankfully hydrogen is relatively easy to sense due to it’s high chemical activity.
So how dangerous is hydrogen fuel? In many situations where a vehicle is located outdoors, hydrogen is safer than conventional liquid fuels or natural gas. This in no way implies that hydrogen is not dangerous — there are many situations where hydrogen, like any other fuel, can cause an accident. As one life-long hydrogen expert said to me once, “Hydrogen is no better, nor worse, than any other fuel. You just have to know the rules for working with hydrogen.” Hence our work and mission.
If you’re thinking about doing a hydrogen experiment at home, best to use caution. Hydrogen, indeed, has the highest flammability range and lowest required ignition energy of any fuel (4%-80% H2 by volume is flammable with air and a grain of sand caught in a jet has enough kinetic energy to ignite a flow). The H2tools.org website has a wealth of information, including accident history to help guide you. Even the pros get caught in tough spots from time to time. Read about our near-miss hydrogen leak event sometime to get a feel for how very un-expected situations in complex systems can lead to risky situations. Regardless, with careful engineering, hydrogen fueled cars have a bright and safe future.