1.2.1 Grouping of Class B Fire Risks
To determine the minimum recommended provision of suitable extinguishers it is convenient to assess premises in the following manner:
• Each room or enclosure should be considered separately.
• Fire risks more than 20 m apart should be considered separately.
• Fire risks sited within 20 m of another fire risk should be assessed either as undivided groups or as divided groups.
Note: Extinguishers should be sited as close as possible to the anticipated point of occurrence. It is undesirable to cover dispersed risks with the same extinguisher(s), with consequent excessive travel distances to reach the fire with an extinguisher. The distance apart of 0 m has been selected as reasonable in view of the danger of rapid spread inherent in class B fires.
1.2.2 Contained Fires
Single open topped containers: The minimum class B rating of an extinguisher or extinguishers recommended for a single open-topped container of flammable liquid (e.g. mixing vessel, spillage in bunded area) can be read directly, from Table 1. The surface area of the container is used to determine the rating.
Undivided group of containers: Containers less than 2 m apart should be considered as an undivided group, equivalent to a single container. The total surface area of all containers in the group is used to determine the recommended rating. The minimum class B rating recommended can be read from Table 1 using this value.
Divided group of containers: Containers more than 2 m, but less than 20 m apart, should be considered as forming a divided group. The surface area of the largest container (or aggregate surface area of the largest undivided group) or one-third of the aggregate surface area of all the containers in the group, whichever is the greater, is used to determine the recommended rating.
The minimum class B rating recommended can be read from Table 1 using this value.
Spillage: The recommended minimum rating of extinguisher to cover spillage of flammable liquid is calculated from the anticipated volume of spillage as follows:
Recommended minimum rating = 10 x volume (in litres) of spillage
The volume of spillage should be assessed according to the particular circumstances. In the case of non-spillproof movable containers it should be assumed that the whole contents of the largest moveable container may spill.
Large volume spillage into restricted areas such as bunds, silled rooms and gullies should not be assessed by the formula given in this clause, but should be regarded as a container fire of area equal to that of the restricted area.
1.2.3 Additional Provision of Extinguishers
It should be borne in mind that the recommendations given in Table 1 are minima and are intended to cover the more common flammable liquids. Where liquids have a low flash point or are especially difficult to extinguish, such as diethyl ether and carbon disulphide, higher rated extinguishers should be provided. In areas protected by fixed systems, portable extinguishers should be provided to cover the risk of spillage or fires originating outside the range of the fixed equipment. Similarly, where high rated extinguishers are installed it is advisable to provide additional low rated extinguishers for use on small fires in preference to the higher rated extinguishers to reduce contamination, replacement costs, etc. and should be sited close to anticipated point of occurrence. These additional extinguishers should be selected according to the recommendations given in Table 1.
1.2.4 Examples: Minimum Provision for Class B Fires (Single Containers)
1.2.4.1 A single tank of surface area 1.0 m² is situated in a room. The recommended minimum rating is found from Table 1 as follows:
• If only one extinguisher is to be installed, 183B (from columns 4 and 1).
• If two extinguishers are to be installed, 89B each (from columns 3 and 1).
• If three extinguishers (foam only) are to be installed, 55B each (from columns 2 and1).
1.2.4.2 A vessel containing a maximum of 200 litres of flammable liquid is positioned within a bund 1.3 m x 1.9 m of suitable depth
The recommended minimum rating is found from Table 1 as follows, using the area of the bund 1.3 x 1.9 = 2.47 m²:
• If only one extinguisher is to be installed, 377B (from columns 4 and 1).
• If two extinguishers are to be installed, 233B each (from columns 3 and 1).
• If three extinguishers (foam only) are to be installed, 144B each (from columns 2 and 1).
1.3. MIXED RATINGS
Where both class A and class B materials are present in the same area extinguishers should be provided to meet both recommendations. The installation of a single type of extinguisher(s), with both class A and class B ratings is recommended in preference to two types, one class A the other class B, taking note of the limitations of the various types.
1.4. RATING OF EXTINGUISHERS MANUFACTURED IN ACCORDANCE WITH OLD BRITISH STANDARDS
Such extinguishers which comply with obsolete standards may be regarded as having ratings not higher than those given below.
Extinguisher type Rating (max)
9 litre water extinguisher 13A
9 litre foam extinguisher 34B
1.5 kg halon 21B
2 kg carbon dioxide 21B
4.5 kg carbon dioxide 34B
3 kg powder 55B
9 kg powder 144B
14 kg powder 233B
Sizes not listed may be regarded as having ratings in general accordance with these values.
Appendix 15.01.04
1. LIMITING OF HALON EMISSIONS
Halons are regarded as ozone damaging chemicals and many countries are now imposing restrictions on their use. The following is recommended for all PETRONAS marketing operations.
The following approaches should be taken to reduce the emission of Halon 1301 and Halon 1211 into the atmosphere:
1.1. EXISTING SYSTEMS
• Stop all release of Halon during training (e.g. release from portable extinguishers); use an alternative such as CO2.
• Generally phase out mobile and portable Halon 1211 extinguishers (replacing by water/foam/CO2/dry powder as appropriate).
• Reduce any systems which are oversized (e.g. total room flooding where cabinet flooding would suffice, or enclosures which could be subdivided).
• Reinforce maintenance procedures to detect leakage from existing systems.
• Test fixed Halon systems without release of Halon 1301 or 1211 (this may require some modification of existing systems).
• Immediately put all automatic Halon 1211 and 1301 total flooding systems at normally manned locations on manual release, to avoid spurious trips and to give the possibility of manual intervention using less (or alternative) extinguishing media. Detection systems, e.g.
heat or smoke detectors, should be realistically tested for rapid response to the specific types of fire which may be expected, to minimise the additional damage which could result from this slower approach.
• Generally remove the Halon 1211 bottles from floating roof tank systems, but ensure adequate detection and alarm. Install fixed or semi-fixed dry riser foam systems on all floating roof tanks which do not already have them (for continuous fire attack). Floating roof tanks in areas where there is a high risk of lightning strikes may require special consideration.
• Generally phase out fixed Halon systems at times of major overhaul. For exceptional circumstances, where Halon is still considered to be essential, total flooding systems should be on manual release only, operated as a last defence, and should be refilled with safe disposal of the Halon, as soon as suitable alternatives become available.
1.2. NEW PROJECTS
• Do not install Halon 1211 mobile and portable extinguishers.
• Do not install fixed Halon systems (possible alternative for unmanned rooms containing major electric/electronic equipment is to use water sprinklers in the room and ceiling void, and CO2 in underfloor areas, after electrical isolation). Protection of unmanned rooms should be based upon manual intervention, with automatic detection and alarm, as appropriate.
For further information or advice please contact PETRONAS.
Appendix 15.01.05
1. FIXED COOLING FOR VERTICAL TANKS 1.1 APPLICATION RATE
For newly constructed tanks which require fixed cooling a minimum water application rate of 1.71/min/m² for the roof and 171/m length of shell circumference should be used (refer Section 15.02.01).
For existing tanks, upgrading of fixed cooling facilities should also be considered. This will be dependent upon:
• Actual tank spacings and general layout.
• Speed and reliability of back-up fire fighting support.
• Strategic importance of the storage facility/possibility of arranging suitable exchange product liftings.
1.2. TANK SEGMENT COOLING
Selective cooling of segments of the total circumference of large tanks may be achieved by installing two (or more) separate spray ring headers at the top of the tank Shell. Separate water delivery lines and valves will also be required. This arrangement will help to limit the required capacity of fire pumps and hydrant lines, and will also reduce the possibility of overloading of bund drainage facilities in the event of a major fire.
2. SPRAY RINGS
Tank cooling should be achieved using stainless steel spray nozzles located on one or more tank top headers as well as on the tank shell. The minimum spray orifice size should be 6 mm to avoid blockage. At this diameter, and at an application rate of 17 litre/m circumference, pressures of around 2.5 to 3.0 bar ex-hydrant will be required. Therefore a pressure reducing device (possibly a length of pipe of restricted diameter) will be needed.
Hot dip galvanized mild steel pipe is recommended for the spray system and all connections should be flanged, which avoids the potential for rusting if screwed connections are used.
A bucket type filter should be installed at each supply manifold with a stainless steel filter element with openings of 3 to 4 mm.
Each tank should have a spray ring header installed at the top of the tank shell with nozzles located up to 450 mm out from the shell plates. Additionally one or more ring headers are to be installed on the roof, as follows:
Tank diameter (m) Number of roof headers Up to 17.5 1
17.5 to 36 2 36 to 52 3
Numbers of spray nozzles on headers will depend on their flow rates and spray pattern characteristics. Including run-down of water from roof headers, all parts of the tank surface should receive 1.7 litres/min/m².
Tanks located 40 m or more from other tankage, pumphouses, loading facilities, etc. do not require fixed cooling arrangements.
2.1. TESTING OF WATER SPRAY SYSTEMS
A major problem associated with water spray systems is blockage of spray jets. Some of the main causes of these blockages are known to be debris left inside the pipes during installation and repairs, gravel and debris carried by the water and corrosion products which originate in the feed lines. The pipes used in water spray systems are hot-dip galvanised and, to preserve their corrosion resistance properties, should only be connected by flanges. This requirement is, however, often neglected. Pipes are cut and welded and, as a result, complete layers of zinc/zinc oxide become detached from the inner walls and form blockages in the system. See Figure 15.01.31 for Typical Dry Riser showing surface and flushing test connections.
The main cause of spray systems failure is, however, the gradual build-up of silt which, in time, hardens and then breaks into lumps large enough to block the nozzle. Frequent flushing of the lines helps to keep them clear but even well maintained systems can suffer blockages if the design of the system allows sediments to accumulate at critical points. The sediments usually enter the system through small, undetected leaks but the ingress of silt and small size gravel during water tests is thought to aggravate the situation. Blockages are often found where there are reductions in pipe diameter and in systems which utilise small bore (4 to 5 mm diameter nozzles).
It is recommended that the dry riser and spray system should be smoke tested every year and fully water tested every three years. The smoke being hydrocarbon generated has a corrosion inhibiting effect in the dry riser and spray rings.
Operation staff are not keen to test water spray systems with water for a number of reasons. In the first place, flooding an installation or depot with water grossly interferes with its normal functions. Even then it is considered a nuisance since all other work must be stopped and all delicate equipment must be protected. Full flow tests require large volumes of water which, in some installations or depots it means the introduction of back- up sea or brackish water into the service-water facility which therefore necessitates fresh water flushing. This can accelerate corrosion and wear in the system which, in the long term, increases the probability of blockages by corrosion products. Poorly drained sections will fill with water during a test and the standing water may subsequently freeze and block a complete section of the system. This problem may not exist in a well designed system but 'dead legs' can be introduced at any time when an installation undergoes repairs or modifications.
In some installations or depots the service water is dirty and will deposit silt and debris in low flow sections of the network. When the demand grows, as when spray systems are water tested, these may be carried by the increased flow and cause blockages. It is claimed that the water coming out of the nozzles leaves dirty stains on painted tank walls, others admit that the whole operation is alien to the normal functions of the plant and, consequently, not very popular. The idea of being able to dry-test water spray systems appeals to those responsible for their maintenance. Dry tests can indeed be very useful especially where water tests are genuinely impossible or difficult to conduct. However, in most cases they can only be considered as a tool which may complement wet tests, not replace them.
The latest development in testing spray systems by using smoke generating equipment produced by 'Acettain Ltd' of London, and is termed the 'PRO-MIST' package. Briefly the package comprises a smoke generator together with an electric motor driven for using mains current and when coupled to a connection in the spray piping can direct smoke over a distance of 150 metres to enable testing and detecting blocked jets in the system. The time taken from start up of the equipment until smoke reaches the jets is about 30 minutes.
The overall dimensions of the equipment is 850 x 50 x 350 mm, weighing 40 kilos. It is not intrinsically safe and must be used accordingly. It is recommended only suitably trained and supervised personnel should use this apparatus. Further details are obtainable from PETRONAS.
FIGURE 15.01.06