Page 399 - Chemical engineering design

SAFETY AND LOSS PREVENTION
Table 9.4.
MF Some typical material factors 373
Heat of combustion
Flash
point ° C MJ/kg
Acetaldehyde 24 39 24.4
Acetone 16 20 28.6
Acetylene 40 gas 48.2
Ammonia 4 gas 18.6
Benzene 16 11 40.2
Butane 21 gas 45.8
Chlorine 1 0.0
Cyclohexane 16 20 43.5
Ethyl alcohol 16 13 26.8
Hydrogen 21 gas 120.0
Nitroglycerine 40 18.2
Sulphur 4 9.3
Toluene 16 40 31.3
Vinyl Chloride 21 gas 18.6
A. Exothermic chemical reactions: the penalty varies from 0.3 for a mild exotherm, such
as hydrogenation, to 1.25 for a particularly sensitive exotherm, such as nitration.
B. Endothermic processes: a penalty of 0.2 is applied to reactors, only. It is increased
to 0.4 if the reactor is heated by the combustion of a fuel.
C. Materials handling and transfer: this penalty takes account of the hazard involved
in the handling, transfer and warehousing of the material.
D. Enclosed or indoor process units: accounts for the additional hazard where venti-
lation is restricted.
E. Access of emergency equipment: areas not having adequate access are penalised.
Minimum requirement is access from two sides.
F. Drainage and spill control: penalises design conditions that would cause large spills
of flammable material adjacent to process equipment; such as inadequate design of
drainage.

Special process hazards

The special process hazards are factors that are known from experience to contribute to
the probability of an incident involving loss.
Twelve factors are listed on the calculation form, Figure 9.2.
A. Toxic materials: the presence of toxic substances after an incident will make the
task of the emergency personnel more difficult. The factor applied ranges from
0 for non-toxic materials, to 0.8 for substances that can cause death after short
exposure.
B. Sub-atmospheric pressure: allows for the hazard of air leakage into equipment. It is
only applied for pressure less than 500 mmHg (9.5 bara).
C. Operation in or near flammable range: covers for the possibility of air mixing with
material in equipment or storage tanks, under conditions where the mixture will be
within the explosive range.