The purpose of the preliminary hazards analysis (PHA) is to identify early in the design process the potential hazards associated with, or inherent in a process design, thus eliminating cost and time consuming delays caused by design changes made later. This also eliminates potential hazard points at design stage itself.
An assessment of the conceptual design is conducted for the purpose of identifying and examining hazards related to feedstock materials, major process components, utility and support systems, environmental factors, proposed operations, facilities, and safeguards. In the proposed plant major hazard is fire due to the storage of chemicals in the tanks. The process related hazards are very rare as the process is carried out in closed reaction vessels and does not involve exothermic reactions. Other hazardous installation is the boiler where the steam is generated and used in the process at various stages.
3.4.6.1 Electrical hazards
Electrical hazards leading to fire and explosion in switchgear and other equipment mainly due to failure of circuit breakers, insulators, fuses, busbars, and poor maintenance. Accidents may also occur in transformer due to open arcing, flashover above oil level, insulator failure, overloading, failure of air cooling system, lighting etc. Nevertheless, all these hazards lead to localized accidents only.
3.4.6.2 Fire hazards
There could be other areas in the plant that have a potential for fire hazard and require adequate firefighting equipment for example, the raw material storages. These are considered here since uncontrolled fire may trigger the above emergencies due to domino effect. However for the proposed plant, safety guidelines will be as per Tariff Advisory Committee.
3.4.6.3
Cable galleries (DG room)
For containment of fire and preventing it from spreading in the cable galleries, unit wise fire barriers with self-closing fire resistant doors are planned. The ventilation system provided in the cable galleries will be interlocked with the fire alarm system so that, in the event of a fire alarm, the ventilation system is automatically switched off. Also to avoid spreading of fire, all cable entries/openings in cable galleries, tunnels, channels, floors, barriers etc., will be sealed with non-inflammable/fire resistant sealing material.
3.4.6.4 Toxic release
The proposed plant will use chorine, which is toxic. If not handled properly, will lead to toxicity. Self-contained breathing apparatus will be available in the plant premises in the event of leakage in case of emergency. Employees will be trained in handling these self-contained breathing apparatus. Since the quantity of toxic release will be on lower side, off site implications of release are not envisaged.
Table 3-17: Preliminary Hazard Analysis for Process/Storage Areas
Equipment Process/Storage Potential Hazard Provision
Turbine Converts pressure in the flue gas into mechanical energy.
Mechanical and fire hazards.
Layout of equipment/ machinery is done in accordance to plant and electrical inspectorate.
Equipment Process/Storage Potential Hazard Provision Generator Converts mechanical energy into electrical energy. Mechanical hazards and fire hazards in Lube oil system Cable galleries Short circuits
As above
Power Transformers
- Fire and explosion All electrical fittings and cables are provided as per the specified standards. Ensure that all electrical cabling in the area are properly insulated and covered. Foam / CO2 / dry
powder type fire extinguishers are to be provided.
Switch Yard Switch Yard Fire As above Switch Yard
control room
- Fire in cable galleries and switch
As above
Boilers - Fire (mainly near
burners), steam; Explosion
As above
DG set Fires in Cable
galleries, Short circuits in Control Rooms and Switch- gears
As above
Natural Gas pipeline
Fire and Explosion Frequent monitoring of valves and joints.
Sprinkling system shall be provided. Ensure that all electrical cabling in the area are properly insulated and covered. Foam / CO2 /
dry powder type fire extinguishers are to be provided. Pipeline design as per OISD norms. Chlorine Used for water
treatment in different phases in cooling water, potable water and raw water.
Toxic accidental release
Leak detection and neutralization system will be provided.
HFO storage (Heavy Fuel)
Combustion at
elevated temperature
LDO Storage Fire
Hydrogen Plant Explosion
HSD Fire
Leak detection and neutralization system will be provided.
Table 3-18: Preliminary Hazard Analysis for the Whole Plant in General PHA Category Description of Plausible Hazard Provision
If there is any leakage and eventuality of source of ignition.
All electrical fittings and cables are provided as per the specified standards. All motor starters are flame proof.
Environ- mental factors
Highly inflammable nature of the chemicals may cause fire hazard in the plant
A well designed fire protection including protein foam, dry powder, CO2 extinguisher should be
provided. Fire extinguisher of small size and big size are provided at all potential fire hazard places. In addition to the above, fire hydrant network is also provided to complete plant.
3.4.7 Safety measures
3.4.7.1 Maximum credible accident (MCA) analysis
Hazardous substances may be released as a result of failures or catastrophes, causing possible damage to the surrounding area. This section deals with the question of how the consequences of the release of such substances and the damage to the surrounding area can be determined. MCA analysis encompasses certain techniques to identify the hazards and calculate the consequent effects in terms of damage distances of heat radiation, toxic releases, vapour cloud explosion, etc. A host of probable or potential accidents of the major units in the complex arising due to use, storage and handling of the hazardous materials are examined to establish their credibility. Depending upon the effective hazardous attributes and their impact on the event, the maximum effect on the surrounding environment and the respective damage caused can be assessed.
Consequence analysis is basically a study of quantitative analysis of hazards due to various failure scenarios. It is that part of risk analysis, which considers failure cases and the damage caused by these failure cases. It is done in order to form an opinion on potentially serious hazardous outcome of accidents and their possible consequences. The reason and purpose of consequence analysis are many folds like:
̇ Part of Risk Assessment
̇ Plant Layout/Code Requirements ̇ Protection of other plants
̇ Protection of the public ̇ Emergency Planning
̇ Design Criteria (e.g. Loading on Control Room)
The results of consequence analysis are useful for getting information about all known and unknown effects that are of importance when some failure scenario occurs in the plant and also to get information as how to deal with the possible catastrophic events. It also gives the workers in the plant and people living in the vicinity of the plant, an understanding of their personal situation.