The captain, Max Pruss, is anxious to get the Zeppelin LZ129 tied down and secured. As the airship floats one hundred feet above the ground, tie down ropes are lowered to the waiting ground crew. In a few minutes the passengers and crew should be safely on the ground; but, before they can disembark, a fire breaks out at the rear of the ship and in less than 37 seconds a blackened, twisted, aluminum skeleton is all that remains of the mighty Hindenburg. The era of hydrogen-filled airships came to an end on that tragic night in 1937. Now, half a century after the disaster, one undeserved legacy still remains. Any mention of the Hindenburg disaster immediately brings to mind the word hydrogen; and hydrogen, disaster, danger and death are all too often considered intimately related. Although the Hindenburg disappeared in a ball of flame, it has been conclusively shown since then that the hydrogen gas giving the great ship its buoyancy was not the source of the fire. It has been proved that the real danger to the airship was the aluminum powder and nitrate doping used on the outer skin to reflect sunlight and reduce interior temperatures. Today, a similar formula is used as rocket fuel. Most of the passengers were burned by the diesel fuel used to power the engines and by the burning fabric cover that gave the airship its shape.

The captain, Max Pruss, is anxious to get the Zeppelin LZ129 tied down and secured. As the airship floats one hundred feet above the ground, tie down ropes are lowered to the waiting ground crew. In a few minutes the passengers and crew should be safely on the ground; but, before they can disembark, a fire breaks out at the rear of the ship and in less than 37 seconds a blackened, twisted, aluminum skeleton is all that remains of the mighty Hindenburg. The era of hydrogen-filled airships came to an end on that tragic night in 1937. Now, half a century after the disaster, one undeserved legacy still remains. Any mention of the Hindenburg disaster immediately brings to mind the word hydrogen; and hydrogen, disaster, danger and death are all too often considered intimately related. Although the Hindenburg disappeared in a ball of flame, it has been conclusively shown since then that the hydrogen gas giving the great ship its buoyancy was not the source of the fire. It has been proved that the real danger to the airship was the aluminum powder and nitrate doping used on the outer skin to reflect sunlight and reduce interior temperatures. Today, a similar formula is used as rocket fuel. Most of the passengers were burned by the diesel fuel used to power the engines and by the burning fabric cover that gave the airship its shape.

There have been several theories presented over the years explaining the cause of the fire; however, most researchers have concluded that, although the hydrogen contributed to the rapid burn of the airship, there is little or no evidence to indicate it actually caused the accident. Yet even now, sixty years after the disaster, the seven million cubic feet of hydrogen gas that gave the ship its buoyancy is still considered unsafe and something to fear. It is my hope that this article will help dispel the general public’s fear of hydrogen and will show that hydrogen, although having some unique properties, is no more dangerous than gasoline, natural gas, propane or any other flammable fuel. In fact, after a review of the historical uses of hydrogen and its excellent safety record, it is hoped that all will understand that this clean and abundant element is superior in many ways to any other commonly used fuel. Rather than seeing the Hindenburg tragedy as a black mark upon the use of hydrogen for fuel, it could be seen as an illustration of the many safety advantages hydrogen has over the more common fuels. Now, let ’s dispel the hysteria that inhibits the broader application of hydrogen as we promote a future hydrogen economy. First, let me take you on a short trip back in time. Long before hydrogen was considered as a fuel source, the Germans were using it as a lifting gas for their famous fleet of Zeppelins. In the first year of the new 20th century, the LZ 1 was first flown. That airship was over 400 feet long and close to forty feet in diameter. It used almost four hundred thousand cubic feet of hydrogen to provide buoyancy. By May 31, 1915, a newer Zeppelin, the LZ 38 had become the first airship to bomb London in World War I. This ship was more than 500 feet long and 60 feet in diameter. It held more than a million cubic feet of hydrogen gas in several bags installed inside its metal skeleton. Bear in mind, when regarding the safety of the hydrogen used in these airships, thousands of animal skins were sewn into bags in which to store the hydrogen. Crew members were known to carry sewing kits to make repairs in flight. They walked along metal catwalks inside the ships framework and had to wear special shoes that reduced static charges. Yet, in spite of the crude nature of the construction, these early airships had remarkable safety records. The LZ 127 better known as the Graf Zeppelin completed over one million miles of travel, including many trans-Atlantic flights while navigating through lightning storms with complete safety. This same technology also proved quite safe in combat in World War I, as many Zeppelins returned riddled with bullet holes. It was not until incendiary projectiles were used that operations in combat were eliminated.
Since we are traveling back in time, let ’s go a little further and discover what the father of the internal combustion engine thought about a choice of fuel. Shortly after our Civil War, a German by the name of Nicolaus Otto developed the four-stroke internal combustion engine. He had several choices of fuel for his new engine. It was common back then to have a ready source of gas to illuminate street lamps and lighting in homes and buildings. Known as producer gas, it was primarily made from coal burned in an air-starved container, thus forming a crude form of hydrogen gas combined with carbon monoxide and trace elements. Another fuel available to Otto was the new waste product of the kerosene industry. It was a volatile and toxic substance and more a nuisance to dispose of than a useful fuel.
He avoided using it primarily because he considered it to be far too dangerous, and that it had little future as a fuel for his new engines. Otto found that using hydrogen or producer gas was far safer and more powerful than this unwanted waste product of the new oil refineries. And what was this nasty, toxic substance? At the time it was known as benzene; but, today we know it as gasoline or petrol. Thanks to the invention of the carburetor this substance is now preferred over Otto’s favorite choice. In spite of gasoline’s dominance in the early 20th century hydrogen still found many uses.

Many will find it surprising that after World War II the use of hydrogen greatly accelerated in an unexpected way. Processed foods became more popular in our affluent new economy, and hydrogen gas found a new use in turning vegetable oils into substitutes for lard and butter. The oil and gas industry had for years used large quantities of hydrogen in refinery processes. Hydrogen also found many uses in the manufacture of specialty metals for jet engines and space vehicles. Miles of pipelines carried hydrogen for these uses for decades, yet the safety record has been excellent. So why does hydrogen have such an undeserved reputation as being dangerous? If you look for the element Hydrogen in a periodic table in most chemistry books you will have little trouble finding it, because it is the first element listed. The listing order is based on the atomic weight of the elements, so it is evident that hydrogen would be the lightest. Hydrogen is also the smallest atom. These properties give hydrogen some unique qualities that can be both an advantage as well as a disadvantage when we use it as a fuel. First let ’s look at the small size of the molecule. Hydrogen has a tendency to pass through solids like metals and plastics and at first glance this may appear to be a problem when looking at the safety of hydrogen use and storage. In reality the rate at which hydrogen gas can pass through metals is extremely low. When connections and fittings using o-rings are properly designed, the permeability rate is very low and causes few problems in terms of loss of fuel or safety. In the case of a leak, hydrogen’s lightness and buoyancy become a definite advantage over the heavier molecules found in propane or gasoline. Unless the leak is severe or the tanks are enclosed in a well-sealed environment, the hydrogen will float upward at a rate of over 17,000 miles per hour, the equivalent of escape velocity. Gasoline and propane will both fall, since they are heavier than air, and will gather in pools or concentrate at the floor or ground level. Hydrogen’s tendency to seek an escape route or to disperse very quickly is a definite advantage.
In tests performed to certify hydrogen tanks for the Department of Transportation, high-velocity bullets and heavy projectiles have been used to penetrate the tanks, and even when the tanks were under pressures greater than 5,000 pounds per square inch there were no explosions of either the tanks or the hydrogen. A tank of gasoline or propane subjected to the same tests would have far different results. The liquid gasoline would spill out and vaporize, and any spark or flame would set it ablaze. A lit cigarette would be sufficient to do this. The same cigarette would not ignite hydrogen. Propane is usually thought of as a gas, but when under pressure in the tank, it is a liquid. A sudden puncture of the tank would cause the propane to expand in volume almost instantly and the vapors would remain at ground level. If the same tank were filled with natural gas, there would be an advantage in it being lighter than air and rising; but, its rate of dispersion would still be far slower than hydrogen.
The real danger in the leak of hydrogen in air is a tendency for explosion. Often it is said that since hydrogen can explode in as little as a 4% air to hydrogen ratio or as high as a 75% air to hydrogen ratio it is “Future generations may still recall the Hindenburg; but, by then, the word hydrogen will be synonymous with clear air and energy freedom, rather than death and disaster.” inherently more dangerous than other fuels. The trick here is that the hydrogen must be confined to be explosive. In most cases this is hard to do especially when proper venting is included in system design. In reality, gasoline in its vapor form can explode in as little as a 1% air to fuel ratio; yet, that fact has not prevented its widespread use. A little research into the Hindenburg tragedy will reveal that even though it contained over seven million cubic feet of hydrogen it did not explode. The thirty-two passengers who perished, either died from burning diesel fuel or jumped to their deaths. Those seventy-seven passengers who certify hydrogen tanks for the Department of Transportation, high-velocity bullets and heavy projectiles have been used to penetrate the tanks, and even when the tanks were under pressures greater than 5,000 pounds per square inch there were no explosions of either the tanks or the hydrogen. A tank of gasoline or propane subjected to the same tests would have far different results. The liquid gasoline would spill out and vaporize, and any spark or flame would set it ablaze. A lit cigarette would be sufficient to do this. The same cigarette would not ignite hydrogen. Propane is usually thought of as a gas, but when lived rode the Hindenburg to the ground as it burned. It took less than thirty seven seconds for complete destruction. If the hydrogen had actually exploded it would have happened all at once and no one would have lived through it. Although it is certain that hydrogen contributed to the burning rate, the lack of confinement prevented an explosion.The energy content of the seven million cubic feet of hydrogen was equivalent to over eighteen thousand gallons of gasoline and was stored above the passengers. One can only imagine the terror and death the spilling and igniting of this quantity of gasoline would have caused.

Even when one compares hydrogen to a more benign fuel such as diesel, the advantage of hydrogen in terms of safety becomes evident. Engineers have speculated that had the airliners flown into the World Trade Center been fueled with liquid hydrogen the buildings would not have collapsed. The jet fuel or diesel was spilled out and pooled on the floors, where it continued to burn until the structural steel was weakened and the ultimate collapse was unavoidable . Hydrogen probably would not have exploded and would have dispersed in just a few seconds. When we take a serious look at hydrogen as a substitute fuel for gasoline, diesel, propane or natural gas, we find its safety advantages far outweigh its few disadvantages. If gasoline or propane had not been in widespread use for the better part of a century, it is doubtful they would have an easy time today getting approval from safety regulators. When we realize that a tank full of gasoline has the explosive power of a stick of dynamite, and we regularly store our vehicles in basement garages, it then becomes apparent that a properly designed vehicle using hydrogen fuel could be parked in the same garage with the same confidence, and that it could be done safely. Although fire and explosion are safety issues in any use of fuel, there is another safety hazard involving gasoline or propane that is most often overlooked. Not only are they both flammable, but they are also extremely toxic. This toxicity is rarely mentioned when making comparisons between competing fuel sources. Hydrogen is completely benign in terms of toxicity. If breathed in, it can displace air or oxygen, but the concentration would need to be quite high to even cause shortness of breath. We don’t often give it much thought, but two-thirds of the water we drink is made up of hydrogen; yet, we cannot live without water. When hydrogen is compared realistically with other fuels in common use, the safety issue soon becomes a non-issue. Proper system design and safety engineering will ensure that a future hydrogen economy will be accepted by the general public and perhaps gasoline and other fossil fuels will be seen in the negative light that once shone unfairly on hydrogen. Future generations may still recall the Hindenburg; but, by then, the word hydrogen will be synonymous with clear air and energy freedom, rather than death and disaster. 