Design the MS227SP Extinguishing System-Part 1

3.1 System Design 

There are two main elements of system design. The first is the risk assessment; determining the type of protection required, considerations such as ventilation, openings and restrictions; equipment location. etc. The second is calculating the quantity of HFC-227ea required, including floor and/or ceiling voids, positioning of nozzles, electrical requirements, etc. 

A Site Survey / Request form is a useful tool to aidememory for addressing the relevant factors and can be used subsequently to substantiate the design criteria. All systems are designed in accordance with the NFPA 2001. 

3.1.1 Hazard Analysis 

The first, and one of the most important, exercises in planning an HFC-227ea extinguishing system is the hazard survey. The information derived from the survey should include risk assessment, environmental conditions, personnel considerations, system operation both in normal conditions and after a discharge, access and construction limitations, dimensions, volumes, and any special requirements. 

HFC-227ea systems are suitable for use in normal commercial and industrial environments. The Minimum Design Concentration for Class A fire is 6.7%, for Class B fire is 8.7% and for Class C fire is 7.0%. All design concentration calculations are based on extinguishing concentrations plus an additional 20% safety factor for Class A and 30% safety factor for Class B. The minimum design concentration for Class C shall be the flame extinguishing concentration of Class A plus an additional 35% safety factor. 

All system design calculations are calculated at minimum design concentration to determine agent quantity. Maximum design concentration should be at the maximum anticipated enclosure temperature, for comparison see NOAEL / LOAEL values. 

Table 3.1 HFC-227ea Cardiac Sensitization 

The flame extinguishing concentration for Class B fuels shall be determined by the cup burner method described in NFPA 2001. The HFC-227ea cup burner valve is 6.7% for commercial grade Heptane. 

The minimum design concentration for a Class B fuel hazard shall be the flame extinguishing concentration for Class B, times a safety factor of 1.3. 

The flame extinguishing concentration for Class A fuels shall be determined by test as part of a listing program. As a minimum, the listing program shall conform to ANSI/UL2127 or ANSI/UL 2166 or equivalent. 

The minimum design concentration for a Class A surface-fire hazard shall be determined by the greater of the following: 

(1) The flame extinguishing concentration for Class A fuels times a safety factor of 1.2.

(2) Equal to the minimum extinguishing concentration for heptane cup burner valve.

The minimum design concentration for a Class C hazard shall be the flame extinguishing concentration for Class A fuels times a safety factor of 1.35. 

The minimum design concentration for spaces containing energized electrical hazards supplied at greater than 480 volts that remain powered during and after discharge shall be determined by testing, as necessary, and a hazard analysis. 

Rugged environments, and those requiring intrinsically safe or flameproof equipment, require special consideration and should be discussed fully with our company before finalising a system design. HFC-227ea is suitable for use with the following materials: 

Class A    Fires involving solid materials usually of an organic nature, in which combustion normally                 takes place with the formation of glowing embers. 

Class B   Fires involving flammable liquids or liquefiable solids and flammable gases. 

Class C    Fires involving energized electrical equipment where the electrical no conductivity of the 

               extinguishing media is of importance. 

Caution. HFC-227ea is not effective on the following: 

Class A Deep seated fires. 

Class D Combustible metals.  

Chemicals capable of auto-thermal recomposition.  Chemicals capable of rapid oxidation.  

Enclosures with hot surfaces (>400 °C) (752 °F) 

3.1.2 Hazard Structure 

The protected enclosure shall be bounded by rigid elements of building construction. The ceiling should be not less than 0.3m (1.ft) above the hazard. The rigid elements should have a fire resistance of not less than 30 min when tested in accordance with BS476: Part 20, Part 21, Part 22 or Part 23 as appropriate. 

During agent discharge, the hazard enclosure will experience a pressure change. The hazard structure must be capable of withstanding a pressure of 1200 Pa (0.402 ft H2O) developed during discharge. 

3.1.3 Hazard Volume 

In total flooding applications the risk area must comprise an enclosed space with no significant openings so that the design concentration can be achieved and maintained. Generally, the calculation is based on an empty area; the subsequent furniture and fittings having little effect on the actual concentration. Similarly, large equipment cabinets and control panels should not be considered in the calculation as it is assumed that the internal area is required to be filled with agent. 

Each enclosed space is considered as a risk area and requires at least one nozzle. A floor void, ceiling void, cable duct, etc., is treated as a separate adjacent area and requires simultaneous discharge to occur. 

Ceiling obstructions such as beams that are less than 300 mm (12") below the slab need not be considered. Obstructions greater than 300 mm (12") can affect the distribution of agent and may require additional nozzles. Consult our company if in doubt. Please note that floor voids cannot be protected separately from the associated room. 

To determine the volume refer to the site drawings, ensuring that the scale is accurate and that heights are denoted, or make a sketch of the area adding dimensions and any relevant details. Calculate the volume of each area.