The SABS has approved and is legislating the adoption of ISO 14520 as the clean agent gas extinguishing standard in South Africa. In this issue, we continue our comprehensive look at this standard.
Extinguishant
General
This clause sets out the requirements for the specifications, system flow calculations and extinguishant concentrations.
Specification, plans and approvals
Specifications
Specifications for gaseous fire-extinguishing systems shall be prepared under the supervision of a person fully experienced in the design of gaseous extinguishing systems and, where appropriate, with the advice of the authority. The specifications shall include all pertinent items necessary for the proper design of the system such as the designation of the authority, variances from the standard to be permitted by the authority, design criteria, system sequence of operations, the type and extent of the acceptance testing to be performed after installation of the system and owner training requirements. Extinguishant specifications are included in the various parts of ISO 14520 for the specific agent (ie Parts 2-15).
Working documents
Layout and system proposal documents shall be submitted for approval to the authority before installation or modification begins. The type of documentation required is specified below. Deviation from these documents shall require permission from the authority.
* Drawings, to an indicated scale of extinguishant distribution system, including containers, location of containers, piping and nozzles (any valves and pressure-reducing devices) and pipe hanger spacing.
* Name of owner and occupant.
* Location of building in which hazard is located.
* Location and construction of protected enclosure walls and partitions.
* Enclosure cross-section, full height or schematic diagram, including raised access floor and suspended ceiling.
* Type of extinguishant being used.
* Extinguishing or inerting concentration, design concentration and maximum concentration.
* Description of occupancies and hazards to be protected against.
* Specification of containers used, including capacity, storage pressure and mass including extinguishant.
* Description of nozzle(s), including inlet size, orifice port configuration, and orifice size/code and orifice size of pressure-reducing devices, if applicable.
* Description of pipes, valves and fittings used, including material specifications, grade and pressure rating.
* Equipment schedule or bill of materials for each piece of equipment or device, showing device name, manufacturer, model or part number, quantity and description.
* Isometric view of extinguishant distribution system, showing the length and diameter of each pipe segment and node reference numbers relating to the flow calculations.
* Enclosure pressurisation and venting calculations.
* Description of fire detection, actuation and control systems.
System flow calculations
General
System flow calculations shall be carried out at a nominal extinguishant storage temperature of 200°C, shall have been validated by an accredited approval authority by appropriate tests as described in ISO 14520, and shall be properly identified. The system design shall be within the manufacturer's specified limitations.
Balanced and unbalanced system
A balanced system shall be one in which:
* Each actual or equivalent pipe length from the container to each nozzle are all within 10% of each other;
* The discharge rate of each nozzle is equal.
Any system that does not meet these criteria shall be considered to be an unbalanced system.
Friction losses
Allowance shall be made for the friction losses in pipes and in container valves, dip tubes, flexible connectors, selector valves, time delay devices and other equipment within the flow line.
Pressure drop
The pressure drop shall be calculated using two-phase flow equations for liquified gases and single-phase flow equations for nonliquified gases.
Valves and fittings
Valves and fittings shall be rated for resistance coefficient or equivalent length in terms of pipe, or tubing sizes with which they will be used. The equivalent length of the cylinder valves shall be listed and shall include syphon tube (where fitted), valve, discharge head and flexible connector.
Piping length
The piping length and nozzles and fitting orientation shall be in accordance with the manufacturer's approved manual to ensure proper system performance.
Drawings
If the final installation varies from the prepared drawings and calculations, new as-installed drawings and calculations shall be prepared.
Liquified gases: specific requirements
Allowance shall be made for changes in elevation as specified in the relevant section of that part of ISO 14520 relating to the specific extinguishant. The minimum discharge rate for liquified extinguishants shall be sufficient to maintain the velocity required for turbulent flow to prevent separation.
Enclosures
The protected enclosure shall have sufficient structural strength and integrity to contain the extinguishant discharge. Venting shall be provided to prevent excessive over or under-pressurisation of the enclosure.
To prevent loss of extinguishant through openings to adjacent hazards or work areas, openings shall be permanently sealed or equipped with automatic closures. Where reasonable confinement of extinguishants is not practicable, protection shall be extended to include the adjacent connected hazards or work areas.
Forced-air ventilating systems shall be shut down or closed automatically where their continued operation would adversely affect the performance of the fire-extinguishing system or result in propagation of the fire. Ventilation systems necessary to ensure safety are not required to be shut down upon system activation. An extended extinguishant discharge shall be provided to maintain the design concentration for the required duration of protection. The volumes of both ventilation system ductworks shall be considered as part of the total hazard volume when determining extinguishant quantities.
All services within the protected enclosure (eg fuel and power supplied, heating appliances, paint spraying) that are likely to impair the performance of the extinguishing system should be shut down prior to, or simultaneously with, the discharge of the extinguishant.
To be continued in the next issue.
For further details contact the FDIA on tel: (011) 397 1618.
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