Design the MS227SP Extinguishing System-Part 2

3.1.4 Ventilation 

If the hazard enclosure has no means of adequate venting after discharge, consideration should be given to installing a normally closed means of ventilation with extraction arrangements which will discharge directly to open air. 

Air conditioning and/or forced ventilation can affect the system performance and the quantity of agent required. 

(i) Self-contained air conditioning unit

A self-contained unit conditions the air within the enclosure and does not rely on a fresh air supply or draw air from other parts of the building. 

If the hazard has a self-contained unit and it is located within the area without an outside air supply, no additional agent is required. It is not necessary to shut down the unit prior to a discharge as the mixing effect is beneficial. 

(ii) Central air conditioning unit

A central air conditioning unit relies on air from outside and is often linked by ducts to other parts of the building, therefore, prior to a discharge, the unit should be shut down and/or dampers operated to close the ducts. Sufficient time must be allowed for the plant to stop or dampers to close, before discharge occurs. Dampers should be installed in both supply and return air ducts, as close as possible to the area. The duct volume between the hazard and the damper must be added to the overall volume. 

3.1.5 Hazard Temperature 

Determine as accurately as possible the anticipated minimum and maximum temperatures likely to be experienced within the protected area. Minimum agent quantity requirements are based on minimum hazard. At maximum temperature, hazard concentration must not exceed the NOAEL/LOAEL values for normally occupied spaces, reference NFPA 2001, Section 1-6 "Safety." 

Once assembled, filled and pressurized the HFC-227ea extinguishing system should not be exposed to temperatures other than the storage / operating temperature range of 0 to 54 °C. (32 °F to 130 °F). This also includes while being in storage or transported. 

3.1.6 Hazard Fuels 

All fuels in the hazard must be identified and the corresponding agent concentration requirements. The design concentration (percent by volume) required for the hazard will be the highest concentration required by any one of the fuels presents in the hazard. 

3.1.7 Personnel Safety 

Natural Agent: To avoid possible injury, avoid any exposure to HFC-227ea in volume concentrations greater than 9% unless using self-contained breathing apparatus. Limit exposure times as in NFPA 2001, Section 1-6 "Safety." 

Symptoms of overexposure to concentrations greater than 10.5% may include dizziness, impaired coordination, 

reduced mental acuity, cardiac effects or unconsciousness. In the event of overexposure, remove to fresh air immediately and summon medical assistance. 

Frostbite: Direct skin contact with HFC-227ea in the immediate area of discharge may cause frostbite. 

3.1.8 Agent Quantities 

Normally the agent quantity is the weight required to produce the desired concentration at the lowest temperature within the hazard enclosure. 

3.1.9 Agent Storage 

HFC-227ea is stored as a liquefied compressed gas in appropriate containers to meet TPED requirements. Nitrogen in the container maintains a super-pressurization of 25 bar at 21°C (360 psi at 70°F) (for 25 bar system) and 42 bar at 21°C (600 psi at 70°F) (for 42 bar system). The chosen location should provide protection from severe weather, mechanical, chemical, or other types of damage. The ambient temperature of the storage area must be between 0℃ to 54°C (32°F to 130°F), the optimum temperature being 21℃(70℉). 

Once assembled, filled and pressurised the HFC-227ea extinguishing system should not be exposed to temperatures other than the storage / operating temperature range of 0 to 54 °C (32 °F to 130 °F). This also includes while being in storage or transported. 

Hydraulic calculations are made at 21°C (70°F). When the storage temperature varies by +5.5 °C (+10°F) from 21°C (70°F), there is a risk that the system will not supply the designed quantity of extinguishing agent. 

In the system design, the limitations for filling and storage of HFC-227ea agent: 

Cylinder fill density: Minimum 0.480 kg/L, Maximum 1.121 kg/L. 

3.1.10 Manifolds 

It may be necessary to manifold agent containers to provide the required amount of agent for a hazard, or to make available the proper increments of agent weight for the protection of multiple hazards. 

Whenever containers are manifolded, the following rules must be observed. 

1. All containers connected to the same manifold or pipe must be the same size and filled with the same agent weight, pressure and fill density. 

2. Agent containers must be located in a single row and spaced according to section.

3.     A connected reserve may be employed in some circumstances providing a secondary supply of agent.

4. Flexible discharge hoses and check valves must be used at each inlet.

In the system design, the limitations for Manifolds: 

Manifold dead volume ratio: Maximum 5.0%. 

3.1.11 Agent Distribution 

Distribution piping will be installed only with approved piping as indicated in Section 5. 

Pipe size reductions may be made by using reducing tees or reducing bushings or reducing couplings.