TABLE OF CONTENTS The explosion of a flammable mixture in a process vessel or pipework may be a deflagration or a detonation. These two types of explosion differ fundamentally and require different countermeasures. Both types, but particularly detonation, can be very destructive.
The conditions for a deflagration to occur are that the gas mixture is within the flammable range and that there is a source of ignition or that the mixture is heated to its auto-ignition temperature.
The conditions for a detonation to occur are similar except that in this case the mixture should be within the detonable range. If the source of ignition is sufficiently strong, detonation may be initiated directly. Alternatively, a deflagration may undergo transition to a detonation. This transition occurs in pipelines but is most unlikely to occur in vessels.
The sources of ignition usually considered are those outside the process plant, but ignition sources can occur inside vessels and pipework also. These include:
flames and hot surfaces;
sparks;
chemicals
unstable compounds,
reactive compounds and catalysts,
pyrophoric iron sulphide;
static electricity;
compression.
This list is sufficient to show that there is no shortage of possible ignition sources inside the plant. The wide variety of conditions which can cause ignition is illustrated by the fact that compressed air at 60 psig striking a suitably shaped depression in the end of a piece of wood can ignite the latter (W.G. High, 1976).
If a flammable...
