Combustible Gases Detector-Transmitter E2638-LEL
User Manual Annex 2 Properties of gases
Acetylene
Synonyms/Trade Names: Ethine, Ethyne
Colourless flammable gas lighter that air. Mixtures with air are explosive.
Results from the interaction of calcium carbide with water. In industrial production,
acetylene is mainly manufactured by the pyrolysis of light hydrocarbons.
Acetylene is widely used for welding and cutting of metals. The usage of acetylene
as a feedstock in chemical industry declines due to cost and environmental
considerations.
Chemical formula
HC≡CH
Molar weight
26
Relative gas density (to air)
0.90
Conversion
1 ppm = 1.06 mg/m
3
Boiling point
-84 °C
Low explosive limit (LEL), % vol in air
2.3* (2.5**)
Upper explosive limit (UEL), % vol in air
100
Odour
Odourless or with a faint ethereal
smell if pure. Commercial grade
may have garlic-like smell due to
impurities.
Hazards
Highly flammable.
Gas/air mixtures are explosive.
Asphyxiant. Non-toxic, but, when
generated from calcium carbide, it
can contain toxic impurities such
as traces of phosphine and arsine.
Exposure limits (NIOSH) REL C
2662 mg/m
3
/2500 ppm
Butane
Butane is colorless flammable gas heavier than air. The term “butane” is used for
any one of two structural isomers (n-butane or isobutane, with unbranched and
branched chain respectively) or for their mixture.
Occurs in light petroleum fractions.
Butane is used mainly as a fuel and as a feedstock in organic synthesis. It is
applied also as a propellant in aerosol sprays and may be used as ozone-friendly
refrigerant.
Mixtures of butane with propane and other hydrocarbons are referred to as LPG
(liquefied petroleum gas).
Chemical formula
n-butane
iso-butane
CH
3
CH
2
CH
2
CH
3
CH
3
CH(CH
3
)CH
3
Molar weight
58
Relative gas density (to air)
2.0
Conversion
1 ppm = 2.38 mg/m
3
Boiling point
-0.56 °C
−11.7 °C
Low explosive limit (LEL), % vol in air
1.4* (1.6**)
1.5* (1.8**)
Upper explosive limit (UEL), % vol in air 8.4
9.6
Odour
gasoline-like odour
Hazards
Highly flammable.
Inhalation of butane can cause
euphoria,
dssiness,
narcosis,
asphyxia,
cardiac
arrhythmia,
fluctuations in blood pressure and
temporary memory loss, when
abused directly from a highly
pressurised container, and can
result in death from asphyxiation
and ventricular fibrillation.
Exposure limits (NIOSH) TWA
1900 mg/m
3
/800 ppm
not established
Hydrogen
Colorless, odorless flammable gas much lighter that air. Mixtures with air are
explosive.
Results from the interaction of acids, bases and water with active metals and from
electrolysis of aqueous solutions. In industrial production, the main source of
hydrogen are hydrocarbons.
Chemical formula
H
2
Molar weight
2
Relative gas density (to air)
0.07
Conversion
1 ppm = 0.0818 mg/m
3
Boiling point
−252.88 °C
Low explosive limit (LEL), % vol in air
4.0
Upper explosive limit (UEL), % vol in air 75
Odour
Odourless
Hazards
Flammable, forms explosive
mixtures with air.
Asphyxiant.
Exposure limits
not established
Methane
Synonyms: Marsh Gas, Natural Gas, Carbon tetrahydride, Hydrogen carbide
Colourless flammable gas, main component of the natural gas, marsh gases.
Methane results from bacterial decomposition of plant and animal matter (landfill
gas).
Methane is widely used as a fuel and chemical feedstock.
Chemical formula
CH
4
Molar weight
16
Relative gas density (to air)
0.55
Conversion
1 ppm = 0.65 mg/m
3
Boiling point
−161.49 °C
Low explosive limit (LEL), % vol in air
4.4* (5.0**)
Upper explosive limit (UEL), % vol in air 15
Odour
Odourless when pure. Methane
used in the kitchens contains
odorant
Hazards
Highly flammable, mixtures with
air are explosive. Asphyxiant.
Exposure limits
not established
Propane
Propane is colorless flammable gas heavier than air.
Occurs in light petroleum fractions.
Propane is used mainly as a fuel and as a feedstock in organic synthesis. It is
applied also as a propellant in aerosol sprays and may be used as ozone-friendly
refrigerant.
Mixtures of propane with butane and other hydrocarbons are referred to as LPG
(liquefied petroleum gas).
Chemical formula
CH
8
CH
2
CH
8
Molar weight
44
Relative gas density (to air)
1.55
Conversion
1 ppm =1.80 mg/m
3
Boiling point
−42 °C
Low explosive limit (LEL), % vol in air
1.7* (2.1**)
Upper explosive limit (UEL), % vol in air
9.5
Odour
Odourless
when
pure.
Commercially available propane
for fuel purposes may contain
odorant (“gas smell”).
Hazards
Highly flammable, mixtures with air
are explosive.
Asphyxiant. May cause dizziness,
confusion, excitation when inhaled.
Exposure
limits
(NIOSH)
TWA
1800 mg/m
3
/1000 ppm
IDLH
2100 ppm [10%LEL]
Terms and abbreviations
TWA: time-weighted average concentration for up to a 8-hour workday during a 40-
hour workweek
STEL: 15-minute TWA exposure that should not be exceeded at any time during a
workday
IDLH (immediately dangerous to life or health): likely to cause death or immediate
or delayed permanent adverse health effects or prevent escape from such an
environment
PEL: permissible exposure limits
REL recommended exposure limits.
A ceiling REL is designated by "C" preceding the value; unless noted otherwise,
the ceiling value should not be exceeded at any time.
NIOSH (National Institute for Occupational Safety and Health): the United States
federal agency responsible for conducting research and making recommendations
for the prevention of work-related injury and illness.
NIOSH data are quoted in this manual where EU regulations are nor accessible.
Conversion of ppm to mg/m
3
is calculated for 25°C and 1 atm.
* according to new EU standards ('stirred' concentration of gas)
** according to US standard (‘still gas’ method)
