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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
autoignition 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.
Copyright Horizon Fuel Cell Technologies – T‐2.5KW_UM_V1.5
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