The flammability limits of ammonia at atmospheric pressure are 15-16% (LFL) and 25-28% (UFL) by volume in the air. These limits associated with low combustion heat greatly reduce the flammability potential of ammonia, which is classified by ASHRAE as a low flammable fluid (6). Several investigations carried out by IIAR (5), ASHRAE (8) and AIChE (9) showed that:
A. In open environments it is only possible to keep ammonia in flame when
evaporates very quickly and the fire is maintained. When ammonia is in the
liquid at atmospheric pressure and it is in equilibrium with the
environment (eg within an open vessel after a leak and already in equilibrium with
the atmosphere, or in the form of a puddle), it is impossible to obtain the ignition of the ammonia mixture
gas with air as its concentration is below the lower limit of
flammability (15-16%).
B. In closed rooms without adequate ventilation it is possible to obtain the ignition of
an ammonia-air mixture within the limits of flammability through a spark
or a constant flame. Therefore, a closed environment represents
a fire hazard, and in this case, the room must be designed for ventilation
which meets minimum dispersion requirements. The IIAR has prepared a technical
(7), with the necessary recommendations for a room ventilation project
machines indoors.
C. The combustion ratio is 50 times slower than a combustible gas (LPG) per
explosion is characterized as deflagration (in the case of LPG it is
characterized as detonation). Explosiveness is 1/7 compared to
explosion of the LPG.
D. The influence of the lubricating oil on the flammability limits will depend on the type of oil and the concentration of the oil in the ammonia. For mineral oils a slight reduction in the upper limit occurs, however, it considerably reduces the lower limit (LFL ~ 12%) to a concentration of 10% by weight of oil in the ammonia, which returns to a small increase to higher concentrations. Considering a synthetic oil with
polyol ester base the reduction is significant for both limits, even at high
oil concentrations (30%), but the range between the limits practically
keeps.
E. The presence of moisture reduces the possibility of ignition of ammonia in the air. The graph below shows the influence of water vapor on the flammability of mixtures
ammonia-air. The values indicate that at 25 ° C all mixtures with
of water vapor greater than 8.2% are non-flammable. So it is also
It is important to use water spray showers at strategic locations.
the installation.
