4.2  Special process hazard

The special process hazards are the factors that are known from experience to contribute to the probability of incident involving loss.

• a.  Toxic materials : after an incident the presence of toxic material at site will make the work of emergency personnel more difficult. The factor applied in this case ranges from 0 to 0.8. Zero implies for non toxic material and 0.8 for materials that can cause death after short exposure.

b.  Low pressure process operating at sub atmospheric conditions allows for the hazard of air leakage into equipments.

c.  Operation in or near flammable limits 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.

d.  Dust explosion risks may arise in processes which involve handling of materials that could create dust. The degree of risk is largely determined by the particle size and nature of the material .

e.  Relief pressure hazard results from the potentially large expansion of fluid to the atmosphere from elevated pressure. Equipment design and operation becomes more crucial as the operating pressure in increased. The factor to apply in this case depends on the relief device setting and physical nature of the process materials.

f.  Low temperature processes allows for the possibility of the embrittlement of carbon steel vessels, or other metals, at low temperatures.

g.  Quantity of flammable material the probable loss will be greater, if greater the quantity of the flammable material in the process or in storage.

h.  Corrosion and erosion of the process unit structure even with good design and material selection, some corrosion and problems may arise in the unit process, both internally and externally. Anticipated corrosion rate predicts the penalty factor. The severest factor is applied if stress corrosion is likely to occur.

i.  Leakage around packings and joints this factor allows for the possibility of leakage from gasket, pump and other shaft seals, and packed glands. The severity of the factor varies where there is a minor leak to the process that have sight glasses, bellows or other expansion joints.

j.  Use of fired heaters providing a ready ignition source boilers and furnaces are heated by the combustion of the fuel and the presence of such units increases the probability of ignition due to leak of combustible material from the process unit. The risk involved depends on the siting of the fired equipments and the flash point of the process material.

k.  Hot oil heat exchange systems in most of the cases heat exchange fluids are flammable and are often used above their flash points, therefore their use in the unit increases the risk of fire or explosions.

l.  Rotating equipment this covers the hazards that arise from the use of large pieces of rotating equipment: compressors, centrifuge, mixers.

Apart from these, in many cases equipment or instruments in the process fails due to thermocouple burnt out, loss of electrical power, steam or cooling water failure, plugging of lines or equipment, etc.