Introduction
Oil refineries hold various chemical substances, including flammables, combustibles, acids and bases in the form of liquids, gases, vapours or solids. Consequently, oil refineries are susceptible to fires due to the nature of these substances. A full surface fuel fire, which may be defined as an inferno that burns petroleum near the exterior of an oil tank, is a common type of fire in the storage areas of petrochemical industries. Full surface fires generate high amounts of radiated heat and induce the structural collapse of tanks. Such fires can spread to adjacent tanks, spill in the bund area, boil over or slop over. Therefore, it is important to extinguish fires promptly to minimise the loss of lives and destruction of property. This report describes the preplanning arrangement for full surface fuel fire at an oil tank refinery.
Operational Preplanning
Handling hazards on-site assumes the worst-case scenario and requires the initiation of the right measures. These precautions include determining the access and egress routes as well as RV points. It is necessary to determine holding areas and other fixed installations within site. Since the firefighting process requires vast resources, water and foam supplies in addition to other firefighting resources should be found. It is important to establish the drainage of water from the fire and the removal of toxic substances to ensure the safety of the firefighting crew. Command functions should also be activated to initiate the firefighting process.
Checking the Wind Direction
Checking the direction of the wind helps to determine the most appropriate firefighting strategies and prevent the inhalation of toxic gases. The wind direction also establishes the course of blazes and areas that are likely to be affected by radiative heat. This step also prevents the spread of fire.
Firefighting Tactics
A defensive firefighting mode is chosen to stabilise the fire and prevent it from worsening. A defensive operation is usually initiated when the fire conditions do not allow attacking the fire from the inside, for example, when a structure is unsafe, and no human lives can be saved. Thereafter, an offensive mode is used.
Offensive firefighting entails approaching the fire to remove its source. This process involves preventing the emission of flammable gases and closing the valve. The firefighting team organises itself into two equal groups in a straight line holding two fire hoses. The team leader stands between the two groups to guide them by tapping the shoulders of the two people at the front of the lines and urging them to move forward. Upon receiving the command, the team members spray the fire with water to protect themselves and their leader. The teams then move forward towards the valve, close it and step back while still facing the regulator. The rule of the operation is to avoid turning their backs towards the fire. Water sprays are used on products with high flash points instead of jets. Water lowers the temperature of the product, stops the vapour and extinguishes the fire. A combination of a jet and spray is appropriate because it projects adequately and offers maximum firefighter protection. Wide-angle sprays expose the valve and cool it, which allows the team to close the regulator and withdraw under spray protection.
Cooling Adjacent Tanks with Water Sprays
The most effective way to minimise tank damage due to fire is by using water spray cooling systems to lower the risk of fire acceleration. A large proportion of heat is conveyed to adjacent tanks by thermal radiation, which may destroy them. Therefore, cooling water is spread over the exterior shells of these tanks. The water absorbs the heat directed at the tanks, thereby lowering the temperature of the reservoirs and minimising the risk of escalation.
Cooling Dry Wall Areas with Water Sprays
The success of fire extinguishing attempts is often determined by the containment of the fire. Prevention of fire spread entails protecting tanks and other structures from radiating heat or direct flames by spraying them with cool water. Streams of cool water should be pointed towards the structures to provide adequate coverage while minimising waste.
Foam Attack onto Burning Surfaces
Covering unburnt oil pools with foam extinguishes the fire and prevents it from spreading. The amount of foam applied depends on the magnitude of the fire. It is important to apply the foam carefully to avoid disturbing the surface and dispersing the burning product.
Pumping Out Tank Inventory
The last step involves removing the fuel source to extinguish the inferno. The source of fuel may be displaced by water or inert substances such as nitrogen gas. However, the use of water to displace the fuel is only recommended if the temperature of the hydrocarbon is lower than the boiling point of water.
Slop Over and Boil Over Hazard
Thermal effects on the stored products can produce several hazardous conditions ranging from slop over to surface boiling due to thermal expansion. During boiling over, a heatwave is produced in the product, which then travels downwards from the burning surface at a rate of 380 to 500 mm per hour. This wave may reach 300 oC, which is above the boiling point of water. When the heatwave reaches the residual water in the bottom of a tank, it turns the water into steam at an expansion ratio of 1700:1. The burning fuel and steam are ejected from the tank violently. The potential spread of such an occurrence could exceed four tank diameters.
Conclusion
Fires present significant challenges for petrochemical facilities. Effective fire extinguishing efforts require the application of strategic procedures. Therefore, expert advice should be obtained from refinery fire workers who have extensive knowledge of the procedures and dangers involved.