 |
HYDROGEN/
SAFETY
source: [www.hydrogennow.org/Facts/Safety-1.htm]
[www.eere.energy.gov/
hydrogenandfuelcells/codes/
basics.html]
|
|
With proper handling and controls, hydrogen can be as safe as, or safer than, other fuels that we use today… - the explosion of the luxury airship Hindenburg at Lakehurst, New Jersey, on May 6, 1937, serves as one of the most spectacular moments recorded by the media. Until very recently, it has aided in paralysing the development of widespread hydrogen use as a fuel, due to concerns for safety (and viewing the fiery pictures of the disaster, understandably so). But knowing the actual nature of the Hindenburg disaster, as well as knowing the behaviour of hydrogen, allows to dispel this stigma associated with hydrogen; (1)
- Like most fuels, hydrogen has a high-energy content and must be handled properly to be safe. In general, hydrogen is neither more nor less inherently hazardous than gasoline, propane, or methane. Hydrogen has been safely produced, stored, transported, and used in large amounts in industry by following standard practices that have been established in the past 50 years. These practices can be adapted for non-industrial uses of hydrogen to attain the same level of safety;
- as the use of hydrogen and fuel cell systems expand, codes and standards will be needed to provide the information needed to safely build, maintain, and operate hydrogen and fuel cell systems and facilities, to ensure uniformity of safety requirements, and to assure local code officials and safety inspectors that sufficient safety standards have been met.
The nature of hydrogen… - Hydrogen is less flammable than gasoline. The self-ignition temperature of hydrogen is 550° Celsius. Gasoline varies from 228-501° C, depending on the grade. When the Hindenburg burned, it took some time before the hydrogen bags were ignited;
- contrary to what some people may believe, hydrogen is not inherently explosive. It must be mixed with air or oxygen before detonation can occur;
- hydrogen disperses quickly. Being the lightest element (fifteen times lighter than air), hydrogen rises and spreads out quickly in the atmosphere. So when a leak occurs, the hydrogen gas quickly becomes so sparse that it cannot burn. Even when ignited, hydrogen burns upward, and is quickly consumed. By contrast, materials such as gasoline and diesel vapours, as well as natural gas are heavier than air, and will not disperse, remaining a flammable threat for much longer;
- hydrogen is a non-toxic, naturally-occurring element in the atmosphere. By comparison, all petroleum fuels are asphyxiants, and are poisonous to humans;
- hydrogen combustion produces only water. When pure hydrogen is burned in pure oxygen, only pure water is produced. Granted, that’s an ideal scenario, which doesn’t occur outside of laboratories and the space shuttle. In any case, when a hydrogen engine burns, it actually cleans the ambient air, by completing combustion of the unburned hydrocarbons that surround us. Compared with the toxic compounds (carbon monoxide, nitrogen oxides, and hydrogen sulphide) produced by petroleum fuels, the products of hydrogen burning are much safer;
- hydrogen can be stored safely. Tanks currently in use for storage of compressed hydrogen (similar to compressed natural gas tanks) have survived intact through testing by various means, including being shot with six rounds from a .357 magnum, detonating a stick of dynamite next to them, and subjecting them to fire at 1500 degrees F. Clearly, a typical gasoline tank wouldn’t survive a single one of these tests.
Just a little bit of wisdom… - No fuel we currently use or have yet to develop will be totally without hazards, through all the processes of production, transportation, and consumption, just as no kitchen knife can be used without risk to the chef;
- hydrogen has long been considered close to ideal as a fuel due to its abundance, non-toxic characteristics, and international availability. We must recognise that each of us has learned to use knives safely, and do so daily. As long as we use wisdom in our methods of production, storage, and use of hydrogen, we’ll enjoy the same safety we have had with petroleum fuels, with the additional benefit of fewer health hazards when leaks do occur;
- safety considerations associated with handling hydrogen include fire, explosion, and asphyxiation. Below is a chart that shows how hydrogen stacks up against some common fuels.
| Properties of Hydrogen, Natural Gas, Gasoline, and Propane(2) | | | Hydrogen | Natural Gas | Gasoline | Propane | | Lower heating value (BTU/lb) | 51,532 | 21,300 | 18,000 - 19,000 | 19,800 | | | | | | | Density at standard conditions (pounds per gallon) | 0.0007 a | 0.005 a | 6.0-6.5 a | 4.22 | | Phase at standard conditions | Gas | Gas | Liquid | Liquid | | Autoignition temperature in air (°F) | 1,050 - 1,080 | 1,004 | 495 | 850 - 950 | | Volume concentrations for flammability in air (%) | 4.1 - 74 | 5.3 - 15 | 1.4 - 7.6 | 2.2 - 9.5 | | Diffusion coefficient in air (inches squared/second) | 0.0946 b | 0.0248 b | 0.008 b | 0.017 c | | Toxicity to humans | Non-toxic, Simple Asphyxiant | Non-toxic, Simple Asphyxiant | Poisonous, Irritant to lungs, stomach and skin | Non-toxic, Simple Asphyxiant |
(1) The Hindenburg disaster was not directly attributable to hydrogen, but to extreme flammability of the outer varnish containing aluminium particles when the vessel was struck by lightning.
(2) Sources: all values are from DOE “Alternative Fuels Data Center” [www.transit-safety.volpe.dot.gov/Publications/CleanAir
/BTS/BTSDesignGuidelines.htm ], except as follows: a)“Clean Air Program: Design Guidelines For Bus Transit Systems Using Hydrogen As an Alternative Fuel”, US Department of Transportation. DOT-VNTSC-FTA-98-6, 1998. Table 2.1 [www.mst.dk/homepage/default.asp?Sub=http://www.mst.dk/udgiv/publications/2002/87-7972-280-6/html/app17_eng.htm]; b)“Hydrogen Energy System: A Permanent Solution to Global Problems”, T. Nejat Veziroglu. University of Miami. Coral Gables, FL; c)“Guidelines on Remediation of Contaminated Sites”. Appendix 5.5, "Physical and Chemical Data." [www.mst.dk/homepage/default.asp?Sub=http://www.mst.dk/udgiv/publications/2002/87-7972-280-6/html/app17_eng.htm]
|
