WO2023173160A1

WO2023173160A1 - Fire suppression system and method

Info

Publication number: WO2023173160A1
Application number: PCT/AU2023/050173
Authority: WO
Inventors: Andrew SPEAR; Stephen STANDLEY
Original assignee: Woodside Energy Technologies Pty Ltd
Priority date: 2022-03-15
Filing date: 2023-03-10
Publication date: 2023-09-21

Abstract

A method of providing fire suppression protection to a substation or electrical switch room (74) containing a plurality of electrical cabinets (16). The method includes installing in each cabinet (16) desired to be provided with fire suppression protection one or more spray nozzles (N). A supply of fire suppressant fluid is held in a tank (12) outside of the cabinets (16). A vessel (22) containing a pressurised propellant gas is connected to the tank (12) through a controllable propellant valve (24). One or more fluid communication paths (18, 20) are provided from the tank (12) to each nozzle (N) in each cabinet (16). In the method involves ongoing monitoring an interior of each cabinet for an indication of a fire or an imminent possibility of a fire. Upon making a positive determination of the existence of a fire or the imminent possibility of a fire in one or more specific cabinets, the propellant valve (24) is opened to force the fire suppressant fluid to flow through a selected one of the one or more fluid communication paths (18, 20) from the tank (12) into at least the one or more specific cabinets (16) and sprayed from the one or more nozzles (N) in the one or more specific cabinets. The method includes hydraulically balancing the fluid communication paths (18, 20), cabinets (16) and nozzles (20) so that a minimum required fire suppressant concentration can be supplied to a most hydraulically disadvantaged cabinet.

Description

FIRE SUPPRESSION SYSTEM AND METHOD

TECHNICAL FIELD

A fire suppression system and method are disclosed. The system and method are particularly well-suited for industrial application, including but not limited to, in relation to electrical risk such as in a substation or electrical switch room.

BACKGROUND ART

Current engineered fire suppression systems which use a gaseous clean agent for electrical risk are limited to room total flood systems. These are designed for fast initial discharge, followed by a 10-minute retention time. The systems are sized for the entire room volume, including any concealed spaces, at the minimum design concentration. The intent of these systems is to effectively extinguish any combustion within the room (smouldering or flame event) at the incipient stages through rapid response, minimising damage to critical or high value equipment. These systems are for asset protection, the intention being to protect property or ensure business continuity, as distinct from for the prevention of loss of life.

Total flood concept is effective where equipment is open, allowing for penetration of the suppression agent to the fire risk areas (e.g., cables, switch gear, battery modules etc.) where battery racks and equipment are open. However, where the fire risk is enclosed, such as compartmentalised IP rated cabinets, ingress of the gas from a room flood system to all cabinet areas at the required concentration can be difficult to achieve, especially in a timely manner. The slower the extinguishment of the fire event, the greater the damage to sensitive electrical equipment not only from heat, but also the acidic and corrosive effects of smoke residue. Existing design and testing of total room flood systems does not address these performance concerns. Other disadvantages with room total flood system are the requirements to maintain integrity of enclosure (room leakage rates) and the potential exposure of emergency response personnel to the extinguishing agent when entering the room post discharge. Also, as the fire risk is typically limited to internal areas of the electrical cabinets, in what may be a large volume room, this results in an unnecessarily large, high maintenance and costly fire suppression system.

The above references to the background art do not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the disclosed fire suppression system and method to any particular form of the fire suppression system and method. SUMMARY OF THE DISCLOSURE

The general idea embodied by the current disclosure is to provide a fire suppression system and method that is capable of delivering a fire suppressant directly into any one of a plurality of cabinets in a common room such as an electrical switch room or substation. The cabinets may include high voltage arc-fault rated cabinets. A benefit of this is the effectiveness of extinguishment is improved and also the overall volume of fire suppressant is reduced from that needed to flood an entire substation or electrical switch room containing the same cabinets. This substantially reduces capex on the fire suppressant itself, as well as opex particularly in the event of a false activation of the system.

A further idea embodied by the current disclosure is to provide a discharge nozzle for the fire suppressant that can be easily adjusted to suit the configuration and volume of the zone and associated cabinets to provide optimum discharge in terms of time, location and atomisation.

In one aspect there is disclosed a method of providing fire suppression protection to a substation or electrical switch room containing a plurality of electrical cabinets comprising: installing in each cabinet desired to be provided with fire suppression protection one or more spray nozzles; holding a supply of fire suppressant fluid outside of the cabinets; connecting a vessel containing a pressurised propellant gas to the supply of the fire suppressant fluid through a controllable propellant valve; providing one or more fluid communication paths from the supply of fire suppressant fluid to each nozzle in each cabinet; monitoring an interior of each cabinet for an indication of a fire or an imminent possibility of a fire; upon making a positive determination of the existence of a fire or the imminent possibility of a fire in one or more specific cabinets, opening the propellant valve to force the fire suppressant fluid to flow through a selected one of the one or more fluid communication paths from the supply into at least the one or more specific cabinets and be sprayed from the one or more nozzles in the one or more specific cabinets.

In one embodiment providing the one or more fluid communication paths comprises connecting the supply by a manifold having one or more branches to the one or more spray nozzles. In one embodiment the method comprises arranging the plurality of cabinets into a plurality of sub-groups of cabinets wherein each branch of the manifold provides a fluid communication path to a respective sub-group of cabinets.

In one embodiment the method comprises hydraulically balancing the fluid communication paths, cabinets and nozzles so that a minimum required fire suppressant concentration can be supplied to a most hydraulically disadvantaged cabinet.

In one embodiment the hydraulic balancing comprises arranging the manifolds so their volume and diameters, and the nozzle discharge flow rate for each fluid communication path from the supply to each of the cabinets will provide a fire suppression fluid flow rate, pressure and residence time of at least a minimum required to suppress a fire in every cabinet, irrespective of a volume of the cabinet or distance from the supply.

In one embodiment arranging the nozzle discharge flow rate comprises forming each nozzle as a body having a plurality of ports and connecting to the ports a selection of (a) one or more spray heads, and (b) none or one or more blank heads, wherein each spray head has at least one outlet opening, and each blank head has no outlet opening.

In one embodiment the method comprises spraying the fire suppressant fluid as a mist into the one or more specific cabinets for a period of at least 3 minutes.

In one embodiment the period is at least 4 minutes.

In one embodiment the period is up to 10 minutes.

In one embodiment the method comprises spraying the fire suppressant fluid to achieve a concentration of about 4.5% within the one or more specific cabinets.

In a second aspect there is provided a fire suppression system for a substation or electrical switch room containing a plurality of high-voltage arc-fault rated cabinets comprising: one or more tanks of a fire suppressant fluid located outside of the cabinets; one or more vessels of a pressurised propellant gas connected to the one or more tanks of fire suppressant fluid; a fire event monitoring system coupled to each of the cabinets for monitoring for an indication of a fire event in each cabinet; one or more spray nozzles in each cabinet; a fluid communication path arranged to enable a flow of the fire suppressant fluid from the one or more tanks of fire suppressant fluid to each spray nozzle; wherein the fire suppression system is arranged so that when the fire event monitoring system identifies a fire event in one or more specific cabinets, pressurised propellant gas is released from the one or more vessels to force the fire suppressant fluid from the one or more tanks and to flow thorough the fluid flow path to into at least the one or more specific cabinets and be sprayed from the one or more nozzles in the one or more specific cabinets.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the fire suppression system and method as set forth in the Summary, specific embodiments will now be described, by way of example only, with reference to becoming drawings in which:

Figure 1 is a representation of an embodiment of the disclosed fire suppression system arranged to provide fire suppression to a zone made up of a plurality of separate cabinets;

Figure 2 is a representation of a nozzle that may be used in an embodiment of the disclosed fire suppression system; and

Figure 3 illustrates an application of the disclosed fire suppression system to a substation housing a plurality of high voltage arc-fault rated cabinets.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Specific embodiments of the disclosed fire suppression system and method will now be described by way of example only. The terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the disclosed fire suppression system and method. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to pertaining to fire suppression system and method. In the drawings, it should be understood that like reference numbers refer to like parts.

Figure 1 is a schematic representation of a first embodiment of the disclosed fire suppression system 10 (hereinafter referred to in general as “system 10”).

The system 10 includes a main cylinder 12 containing a volume of a fire suppressant agent such as NOVEC™ 1230 fire protection fluid manufactured by the company 3M. When in the main cylinder the fire protection fluid is in the form of a liquid. The cylinder 12 may also contain a volume of a propellant gases such as nitrogen for delivering the fire suppressant to a discharge nozzle.

In Figure 1 the system 10 is in selectable fluid communication with each of four separate electrical cabinets 16a-16d (hereinafter referred to in general as cabinet 16 in the singular, or cabinets 16 in the plural), that are arranged to form a bank 14 of cabinets. The system 10 can direct fire suppressant to flow into a selection one or more of the four cabinets 16 in the bank 14. The selection of cabinets is on the basis of the system 10 detecting a fire or an imminent possibility of a fire (hereinafter “a fire event”) in the cabinets. So, the suppressant is only delivered into the cabinet 16 in which there is believed to be a fire event to the exclusion of other cabinets in the same bank 14. The cabinets 16 can be of the same or different internal volume. The capacity of the system 10 and in particular the main cylinder 12 is designed to meet the largest demand (i.e. , volume of the largest cabinet 16). For example, in this embodiment the volume of the main cylinder 12 is designed to be sufficient to continuously deliver the fire suppressant fluid for the desired time and to achieve a desired concentration for the purposes of extinguishing a fire in the largest one of the cabinets 16a-16d, which this case is either of cabinets 16c or 16d. As a consequence, if a fire is detected in one of the smaller cabinets connected to the same system 10/cylinder 12, the system 10 may provide the fire suppressant fluid for a longer period and/or a higher concentration.

A fire suppressant distribution manifold 18 provides fluid communication between the main cylinder 12 and each cabinet 16 in the group 14. The manifold is formed with a plurality of branches 20a-20d (hereinafter referred to in general as “branch 20”, or “branches 20”) each capable of delivering fire suppressant fluid to a respective cabinet 16a-16d. Located in each of branches 20a-20d outside of a corresponding cabinet 16 is a respective selector valve Va- Vd (hereinafter referred to in general as “valve V” or “valves V”). Inside each cabinet 16a- 16d, connected to an end of a corresponding branch 20 is a group of one or more nozzles Nij (hereinafter referred to in general as “nozzle N” or “nozzles N”). For cabinet 16a the nozzle group comprises only the single nozzle Na1; for cabinet 16b the nozzle group comprises Nb1 and Nb2; for cabinet 16c, the group comprises Nc1, Nc2, Nc3 and Nc4; and for cabinet 16d, the group comprises Nd1, Nd2, Nd3 and Nd4. The branches 20 pass into the cabinets 16 to supply fire suppressant fluid to the nozzle groups Nij either through existing penetrations or custom-made penetrations. This is dependent on the nature of the cabinets 16. The system 10 may incorporate any one or more known fire detection systems or mechanisms such, as but not limited to: an aspirated smoke detector system; and, a linear fibre-optic heat detection system. The specific nature of the fire detection system (s) incorporated in the system 10 is not a critical or essential feature of the overall system 10.

The system 10 includes a propellant cylinder 22 in fluid communication with the main cylinder 12. The propellant cylinder 22 contains a volume of an inert compressed gas. In this embodiment the propellant is compressed nitrogen and the fire suppressant fluid is NOVEC™ 1230 fire protection fluid.

The propellant cylinder 22 is fitted with a head valve 24 which includes a bursting safety disc. The head valve 24 is connected via a flexible hose 26, a pressure regulating orifice 27, and one-way valve 28 to the main cylinder 12. The head valve 24 is also connected to an activation unit 30, which can receive signals from an electronic control unit 32. A local manual release lever 34 is connected to the activation unit 30. Operation of the lever 34 facilitates operation of the system 10 in the event of a failure of the electronic control unit 32 to operate the activation unit 30. In one embodiment the cylinder 22 may have a volume of about 67 L and carry nitrogen pressurised to 124 barg.

The main cylinder 12 is fitted with a head valve 36 and is in fluid communication with a siphon tube 38 which extends into the cylinder 12, and a hose 40 which connects to the manifold 18 through a one-way valve 42. A pressure sensor Pm is placed in the manifold 18 upstream of a vent 44. In one embodiment the internal diameter of the manifold 18 may be in the order of 15 mm, with the internal diameter of the branches 20 being about 10 mm.

The operation of the system 10 is as follows. When the electric control unit 32 receives an activation signal (for example from a fire or smoke detection system which monitors the internal smoke /fire status of the cabinets 16), the activation unit 30 operates the valve head 24 mounted on the N2 cylinder 22. This releases N2 gas at a pressure of 124barg. The pressurised N2 gas flows through the hose 26, the pressure regulating orifice 27, and the one-way valve 28 into the main cylinder 12. Due to the operation of the orifice 27 the N2 gas pressurises the fire suppressant fluid in the main cylinder 12 to about 25-27 barg. The subsequently pressurised fire suppressant fluid in the main cylinder 12 is forced up the siphon tube 38 and through the valve 36 to the hose 40. The suppressant fluid then flows through the one-way valve 42 to the manifold 18. Pressure sensor Pm signals the release of agent to the control room. Depending on the location of the detected fire event, the appropriate valve Va-Vd will be automatically opened to allow the fire suppressant fluid to flow into the associated cabinet in which the fire event is detected. The associated nozzles Nij operate to discharge the fire suppressant fluid, atomised as a fine mist to vaporise the fluid and thereby protect space within the cabinet 16.

Figure 2 illustrates an embodiment of a nozzle N that may be incorporated in the system 10. In a general sense the nozzle N has a body 60 provided with a plurality of spaced ports 62. Each port 62 can receive either a spray head 64 or a blank head 66. The number of spray heads 64 and blank heads 66 used in the nozzle N can be varied having regard to the location of the nozzle N within a cabinet 16, the desired spray atomisation, and discharge rate to suit cabinet volume and layout of internal equipment and gear, ensuring minimum fire suppressant fluid concentrations for the purposes of fire suppression.

In this embodiment the body 60 has a hexagonal shape, in axial cross section, with six ports 62 evenly spaced about a central axis 68, and a single port 62 in one end face 70. Each spray head 64 is formed with a single central opening 72. An end of the nozzle N opposite the end face 70 forms an inlet and is provided with a threaded connector 73 for screw fitting to an associated manifold branch 20. The discharge flow rate for each nozzle N can be individually tuned by the connection of spray heads 64 and blank heads 66 to best suit the location of the nozzle within the cabinet as well as the pressure of the supply of the fire suppressant fluid. The tuning of the nozzles may also be affected by changing the size, number and configuration of the outlet openings 72 in the spray heads 64.

Figure 3 illustrates how embodiments of the disclosed system 10 may be used to provide fire protection to a high voltage electrical switch room 74. Significantly, instead of operating to suppress fire within the entirety of the volume of the switch room 74, respective systems 10a- 10d are installed to provide fire protection for specific groups 14a, 14b, 14c, and 14d of cabinets which are located within the switch room 74. Each system 10a-10d is of the substantially same construction and operation as the system 10 described above.

The system 10a operates to provide fire protection to a selected region or cabinet in the cabinet group 14a. The group 14a comprises two separate and spaced apart cabinets 16a1 and 16a2. The cabinet 16a1 encloses a relatively large volume and in this embodiment is notionally divided into two regions Rx and Ry. The manifold 18a feeds three branches 20x, 20y, 20z through respective selector valves Vx, Vy and Vz. Branches 20x and 20y provide a path for feeding feed fire suppressant to the regions Rx and Ry respectively in the cabinet 16a1. The branch 20z feeds fire suppressant to the cabinet 16a2. There are ten nozzles N for each of the branches 20x and 20y, and twelve nozzles N for the branch 20z. The system 10a is able to detect and suppress fire within the confines of its specific cabinet group 14a. When a fire event is sensed by the system 10a in one of the: region Rx; region Ry; or, the cabinet 16a2; the corresponding selector valve Vx, Vy, Vz is opened (the others remaining closed) and the fire suppressant fluid is pressurised by the compressed N2. The fire suppressant fluid flows through the manifold 18 to the opened selector valve and through the associated branch to be discharged into the region/cabinet as an atomised mist by the corresponding nozzles.

The system 10b provides fire protection to the cabinet group 14b. The group 14b comprises a bank of four cabinets 16b1-16b4 which are coupled together, each cabinet being of the same volume. In this embodiment there is no valve in the manifold 18b, so the manifold 18b of system 10b supplies fire suppressant fluid to all the nozzles N in all of cabinets 16b1-16b4 when smoke or fire is detected in any one of the cabinets 16b1-16b4. Although in a variation an optional valve Vb could be placed in the manifold 18 between the associated supply of fire suppressant fluid and the nozzles in the cabinets 16b1-16b4. The valve Vb is opened when a fire event is detected in any one of the cabinets 16b1-16b4.

The system 10c provides fire protection to the cabinet group 14c which comprises a single bank of thirty one connected cabinets. The system 10c has a manifold 18c which splits into two main branches 20v and 20w. The branch 20v is itself further branched to provide a fluid communication path from a supply fire suppressant fluid of the system 10c to each of fourteen cabinets in a first sub-group of cabinets 14csv, while branch 20w supplies fire suppressant fluid to each of seventeen cabinets in a second group of cabinets 14cw. Each of the cabinets in the group 14c has a single nozzle. It should also be noted that some of the cabinets within each of the sub-groups 14cv, 14cw are of different volume to the others.

The system 10d provides fire protection to the cabinet group 14d which comprises a single bank of thirty four connected cabinets which are arranged in three sub-groups 14dp, 14dq and 14dr. The manifold 18d of system 10d is split into three main branches 20p, 20q and 20r which supply fire suppressant fluid to each individual cabinet in the group 14dp-14dr respectively through corresponding valves Vp, Vq and Vr. To do so, each branch 20p, 20q, and 20r is itself further branched to provide a fluid communication path to individual nozzles in each cabinet within its sub-group.

To minimise the volume of the fire suppressant fluid required to be held in a cylinder 12 in each of the systems 10a, 10c and 10d described above there is an individual valve V for each branch that operates and is controlled in the same way as described above in relation to the system 10 illustrated in Fig 1. Each branch supplies fire suppressant to one or more cabinets or a region within a cabinet.

From the above description it should be appreciated that the system 10 enables a relatively large volume (for example the total volume of the cabinet banks 14a, 14c, 14d) to be segregated into smaller regions or areas (e.g., for bank 14a: the regions Rx, Ry and cabinet 16a2). The effect of this is that the relatively large volume is protected by a smaller volume of fire suppressant fluid than would otherwise be required. However, for very small areas such as in the cabinet bank 14b, no segregation is required.

Generally, high voltage cabinets 16 are not sealed and have relatively high fluid leakage rates. In this event, embodiments of the system 10 are arranged so that discharge of the fire suppressant fluid does not follow conventional total flood systems which advocate discharging within 10 seconds, but rather will provide a slow and controlled release. In one embodiment the system is configured and operated to provide a controlled continuous release of the fire suppressant fluid as an atomised mist for a specified minimum time, for example, but not limited to, 3 minutes, 5 minutes or 10 minutes and to provide a concentration required for extinguishment of about 4.5% to 6% for the cabinet or region in which a fire event has been detected. Thus, for example in one embodiment the fire suppressant fluid may be continuously released as an atomised mist for more than 5 minutes including up to about 10 minutes, with a fire suppressant concentration of say 5%.

The provision of multiple ports on the nozzles enables the selective placement of spray heads 64 and blanks 66 to target location of fuel within the cabinet. The duration of discharge can be supported by the addition of one or more optional reserve cylinders to achieve the required hold-up (i.e., release) time. The quantity of fire suppressant fluid held in the system 10, the number of fire suppressant cylinders 12 actuated and hydraulic balancing, can be arranged to ensure the minimum required fire suppressant concentration at the hydraulically most disadvantaged cabinet/region for the specified time. Hydraulic balancing may be achieved by using piping and tubing diameters, and the nozzle configuration (i.e., including the number and size of spray heads 64), and the pressure regulating orifice 27. Each fluid communication path from the supply to each of the cabinets 16 will provide a fire suppression fluid flow rate, pressure and residence time of at least the minimum required to suppress a fire in every cabinet, irrespective of its volume or distance from the supply 12. This is believed to provide a cost-effective option as the fire is dealt with at the source and at its incipient stage, preventing extensive damage to the most critical equipment and minimizing the need for extensive clean-up and time for return to service. Also, by virtue of the system 10 delivering the fire suppressant fluid directly to the enclosed zones/cabinets potential for personnel exposure to the released fluid is eliminated and therefore provides as low a risk as possible.

While several exemplary embodiments of the system and method have been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. For example, in the present embodiment if a fire event is detected in one cabinet, the system is operable to supply the fire suppressant gas to not only that one cabinet but every other cabinet that is fed via the same branch 20/valve V. So, with reference to Figure 3 and looking at the system 10b there are four separate cabinets in the cabinet bank 14b. On detection of a fire event in say the cabinet 16b1, fire suppressant is supplied to every cabinet. However, if desired, notwithstanding the added complexity, it would be possible to add an individual valve for each nozzle N in each of the four separate cabinets. In this way suppressant fluid would be discharged only into the cabinet in which the fire event is detected, to the exclusion of the other cabinets. In a more sophisticated arrangement, when a manifold 18 or branch 20 supplies multiple cabinets in a bank, it would be possible to operate the valves at each nozzle to supply the fire suppressant fluid to the cabinet in which a fire event is detected, and say one cabinet on either side. It should also be appreciated that the exemplary embodiments of the fire suppression system and method are only examples, and are not intended to limit the scope, applicability, or configuration of the present disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the disclosed fire suppression system and method.

In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word “comprise” and variations such as “comprises” or “comprising” are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the system and method as disclosed herein.

Claims

1. A method of providing fire suppression protection to a substation or electrical switch room containing a plurality of electrical cabinets comprising: installing in each cabinet desired to be provided with fire suppression protection one or more spray nozzles; holding a supply of fire suppressant fluid outside of the cabinets; connecting a vessel containing a pressurised propellant gas to the supply of the fire suppressant fluid through a controllable propellant valve; providing one or more fluid communication paths from the supply of a fire suppressant fluid to each nozzle in each cabinet; monitoring an interior of each cabinet for an indication of a fire or an imminent possibility of a fire; upon making a positive determination of the existence of a fire or the imminent possibility of a fire in one or more specific cabinets, opening the propellant valve to force the fire suppressant fluid to flow through a selected one of the one or more fluid communication paths from the supply into at least the one or more specific cabinets and be sprayed from the one or more nozzles in the one or more specific cabinets.

2. The method according to claim 1 wherein providing one or more fluid communication paths comprises connecting the supply by a manifold having one or more branches to the one or more spray nozzles.

3. The method according to claim 2 comprises arranging the plurality of cabinets into a plurality of sub-groups of cabinets wherein each branch of the manifold provides a fluid communication path to a respective sub-group of cabinets.

4. The method according to claim 3 comprising hydraulically balancing the fluid communication paths, cabinets and nozzles so that a minimum required fire suppressant concentration can be supplied to a most hydraulically disadvantaged cabinet.

5. The method according to claim 3 wherein hydraulic balancing comprises arranging the manifolds so their volume and diameters, and a nozzle discharge flow rate for each fluid communication path from the supply to each of the cabinets will provide a fire suppression fluid flow rate, pressure and residence time of at least a minimum required to suppress a fire in every cabinet, irrespective of a volume of the cabinet or distance from the supply. The method according to claim 5 wherein arranging the nozzle discharge flow rate comprises forming each nozzle as a body having a plurality of ports and connecting to the ports a selection of (a) one or more spray heads, and (b) none or one or more blank heads, wherein each spray head has at least one outlet opening from which the fire suppressant fluid can be sprayed, and each blank head has no outlet opening. The method according to any one of claims 1-6 comprising spraying the fire suppressant fluid as a mist into the one or more specific cabinets for a period of at least 3 minutes. The method according to claim 7 wherein the period is at least 4 minutes. The method according to claim 7 wherein the period is up to 10 minutes. The method according to any one of claims 1-9 comprising spraying the fire suppressant fluid to achieve a concentration of between 4.5% to 6% within the one or more specific cabinets. A fire suppression system for a substation or electrical switch room containing a plurality of high-voltage arc-fault rated cabinets comprising: one or more tanks of a fire suppressant fluid located outside of the cabinets; one or more vessels of a pressurised propellant gas connected to the one or more tanks of fire suppressant fluid; a fire event monitoring system coupled to each of the cabinets for monitoring for an indication of a fire event in each cabinet; one or more spray nozzles in each cabinet; a fluid communication path arranged to enable a flow of the fire suppressant fluid from the one or more tanks of fire suppressant fluid to each spray nozzle; wherein the fire suppression system arranged so that when the fire event monitoring system identifies a fire event in one or more specific cabinets, pressurised propellant gas is released from the one or more vessels to force the fire suppressant fluid from the one or more tanks and to flow thorough the fluid flow path into at least the one or more specific cabinets and sprayed from the one or more nozzles in the one or more specific cabinets.