Hydrogen Safety


Hydrogen is a medium for storing energy, otherwise known as an energy carrier. All energy carriers and fuels, such as gasoline and natural gas, have the characteristic of being volatile (containing potential energy). Hydrogen's benefits and disadvantages differ from the fossil fuels commonplace in an advanced energy utilizing society such as in the United States.

In order to have a clear picture of hydrogen's advantages and disadvantages, the following paragraph contains the facts surrounding hydrogen.

Hydrogen is an odorless and colorless gas, due to its boiling point of -252.77o C. Its density of 0.0899 grams/liter make it lighter than the surrounding air and bestows the ability to rapidly dissipate if released into the atmosphere or spilled onto the ground. According to "Hydrogen in the Energy Sector" by Dr. Zittel; et al., when comparing energy density by weight, "hydrogen has the highest energy to weight ratio of all fuels. 1 Kg of hydrogen contains the same amount of energy as 2.1 Kg of natural gas or 2.8 Kg of gasoline." To clarify a point, hydrogen ranks last when the comparing energy density by volume. Hydrogen possesses 2.36 kWh/liter as a liquid, natural gas contains 5.8 kWh/liter and gasoline registers at 8.76 kWh/liter. These facts are relevant to the analogy of the size of a hydrogen tank and the size of a comparable gasoline tank as well as the explosion hazard associated with the fuels.

Hydrogen is non-toxic
Gasoline and oil are extremely toxic and poisonous to humans and wildlife alike when unintentionally released into the environment. If a hydrogen spill occurred, the hydrogen would evaporate almost immediately leaving only water behind. Oil and gasoline, on the other hand, require immense clean up efforts with the result being that most of the spilled toxic gasoline or oil seeps into the surrounding ecosystem wreaking irreparable harm.

In order to burn, hydrogen requires a higher concentration in the atmosphere than other fuels
When hydrogen approaches levels of 4% concentration in the atmosphere, the possibility of it igniting increases greatly. A concentration level of 4% for hydrogen does not seem that high, but when compared to gasoline, which is 1%, hydrogen offers a significantly lower risk of explosion. Gasoline becomes volatile at a concentration 4 times lower than that of hydrogen.

Hydrogen's Properties vs. Other Fuels
The properties that are characteristic of hydrogen allow hydrogen to have many advantages over fossil fuels in terms of safety. Hydrogen's low density and ability to rapidly disperse allow hydrogen to escape to the atmosphere if a leak occurred. Propane and gasoline, with their high densities and slow dispersal allow the fuels to congregate near the ground increasing a risk of explosion. Hydrogen has to reach a concentration of 4% in the surrounding atmosphere before hydrogen poses a danger. Gasoline's concentration only has to reach 1% before the danger of ignition is apparent. The chart below contains the characteristics of gasoline, methane and hydrogen relating to ignition and explosion hazards.

Characteristics Related to Fire Hazards of Fuels*

Property Gasoline Methane Hydrogen
Density (Kg/M3)
Diffusion Coefficient In Air (Cm2/Sec)
Specific Heat at Constant Pressure (J/Gk)
Ignition Limits In Air (vol %)
Ignition Energy In Air (Mj)
Ignition Temperature (oC)
Flame Temperature In Air (oC) Explosion Energy (G TNT/kj)
Flame Emissivity (%)		 4.40
0.05
1.20
1.0-7.6
0.24
228-471
2197
0.25
34-43		 0.65
0.16
2.22
5.3-15.0
0.29
540
1875
0.19
25 -33		 0.084
0.610
14.89
4.0-75.0
0.02
585
2045
0.17
17-25

* T. Nejat Veziroglu. Hydrogen Energy System: A Permanent Solution to Global Problems. University of Miami, Coral Gables, FL 33124, USA


Hydrogen has suffered from image problems in the past
Hydrogen is commonly associated with two things; the Hindenburg disaster and the hydrogen bomb. Recently, researchers to determine the exact cause of the fire have investigated the Hindenburg accident.

In 1937 the Hindenburg was destroyed attempting to land in an electrical storm outside of Lakehurst, NJ. Witness reported observing a blue glow on the top of the ill-fated airship. The blue glow is often indicative of extremely high electrical activity. The current school of thought indicates that the electricity around the skin of the ship probably ignited the skin. Addison Bain, a retired NASA safety expert, has analyzed the remaining fragments of the zeppelin's exterior fabric skin. His findings indicated that the skin was composed of either cellulose nitrate or cellulose acetate. Aluminum flakes were combined with these materials to reflect sunlight in order to keep the airship cool. The combination of cellulose nitrate and aluminum is commonly known today as the recipe for rocket fuel, as anyone who has watched a rocket launch knows, is highly explosive. The hydrogen contained in the airship did burn, but remember that hydrogen is lighter than air and the flames would have been streaking upwards not down onto the passenger cabin. All of the people who died in the disaster, died from falling to their death or burning to death from flaming, dripping diesel fuel. All of the survivors rode the airship down to the ground and safety.

The size of the Hindenburg needs to be kept in mind. A fuel cell passenger car operating on hydrogen would never have such a large amount of hydrogen stored in a flimsy cloth bag. All of the fuel cell systems and hydrogen storage techniques are engineered with safety being a paramount concern. The composite tanks used to store liquid and gaseous hydrogen are required to undergo rigorous safety testing before they are certified for hydrogen storage.

The other reason hydrogen has received negative press in the past is its relationship to the hydrogen bomb. In order for hydrogen atoms to fuse together, like the reaction in a hydrogen bomb, special circumstances have to occur. Hydrogen will only fuse under extremely high heat and pressures. The enormous pressures required for hydrogen atoms to fuse would never occur in a fuel cell system or hydrogen storage device.

Hydrogen is an energy carrier and possesses similar characteristics inherent to any of the fossil fuels commonly used by today's society. When education and correct handling methods are applied, hydrogen is actually safer than many common fuels already in widespread use. Unfortunately, hydrogen has been associated with some tragic events in the past. Aside from some negative press, hydrogen is poised to revolutionize the way society generates energy and potentially eliminate the detrimental environmental effects associated with energy use in the present day.