6
1.5 Flammability and volatility
Hydrogen is flammable over concentrations of 4 – 75% by volume in air, and is explosive
over concentrations of 15 – 59%. As a result, even small leaks of hydrogen have the
potential to burn or explode. Leaked hydrogen can concentrate in an enclosed
environment, thereby increasing the risk of combustion and explosion.
Hydrogen flames are pale blue and are almost invisible in daylight due to the absence of
soot. Due to its high buoyancy and diffusivity, burning hydrogen rises unlike gasoline,
which spreads laterally.
A flammable or explosive hydrogen mixture is easily ignited by a spark or even a hot
surface. The auto-ignition temperature of hydrogen is 500 °C (932 °F). The energy of a
hydrogen gas explosion is 2.4 times that of gasoline or methane for an equal volume.
Hydrogen gas explosions are therefore more destructive and carry further.
WARNING!
A mixture of hydrogen and air is potentially flammable and explosive and can be ignited
by a spark or a hot surface.
As in the presence of any fuel, all sources of ignition, including smoking, are not
permitted in the vicinity of the stack.
WARNING!
Keep all sources of ignition away. Smoking is not permitted in the vicinity of the stack.
1.6 Oxygen Depletion
Oxygen is a colourless, odourless, non-toxic and tasteless gas. Oxygen is essential for
life in appropriate concentrations.
Ambient air contains up to 21% oxygen. Oxygen levels below 19.5% are biologically
inactive and may act as simple asphyxiants. Effects of oxygen deficiency may include:
rapid breathing, diminished mental alertness, impaired muscular coordination, faulty
judgement, depression of all sensations, emotional instability, and fatigue. As
asphyxiation progresses, nausea, vomiting, prostration, and loss of consciousness may
result, eventually leading to convulsions, coma, and death. At concentrations below
12%, immediate unconsciousness may occur with no prior warning symptoms.
WARNING!
Lack of oxygen can lead to unconsciousness and asphyxiation.
As a preventative measure, the stack must be operated in a well-ventilated area in order
to compensate for the oxygen used within the fuel cells.
WARNING!
Always operate the stack in a well-ventilated area.