Design proposals must be prepared by qualified professionals to ensure that the proposed design does not exceed the toxicity threshold.

When studying gas‑fire suppression systems, the most challenging aspect is undoubtedly the myriad design parameters. It’s easy to get confused between design pressure, maximum operating pressure, and relief‑action pressure, while the distinctions among heptafluoropropane, IG‑541, and carbon dioxide can be equally perplexing. Today, Xinlin Fire Protection will break down these concepts in detail, highlighting the similarities and differences in the design parameters of various extinguishing agents, helping you clarify your thinking and learn through comparison.

I. Applicable Fire-Prone Areas

Heptafluoropropane and IG541 systems: ① Fires on solid surfaces; ② Liquid fires; ③ Gas fires where the gas supply can be shut off prior to extinguishing; ④ Electrical fires.

Carbon dioxide systems are suitable for: ① solid-surface fires and deep-seated fires involving certain solids such as cotton, wool, textiles, and paper; ② liquid fires or fires involving fusible solids like paraffin wax and asphalt; ③ gas fires where the gas supply can be shut off prior to extinguishing; and ④ electrical fires.

II. Places Not Subject to Fire Regulations

Heptafluoropropane and IG‑541 systems: ① Fires involving oxidizers such as nitrocellulose or sodium nitrate, or chemical products containing oxidizers; ② Fires involving reactive metals; ③ Fires involving metal hydrides such as potassium hydride or sodium hydride; ④ Fires involving chemically unstable substances that can decompose spontaneously, such as hydrogen peroxide or hydrazine; ⑤ Deep-seated fires of combustible solid materials.

Carbon dioxide systems are suitable for: ① fires involving oxidizing chemical substances such as nitrocellulose and gunpowder; ② fires involving reactive metals (Class D fires); ③ fires involving metal hydrides such as potassium hydride and sodium hydride.

III. Fire Extinguishing Mechanism

Heptafluoropropane: cooling, asphyxiation, and chemical inhibition; it has a greenhouse effect, and the extinguishing agent is stored in liquid form.

IG541: Asphyxiant, with no greenhouse effect; the extinguishing agent is stored in gaseous form.

Carbon dioxide: asphyxiant, cooling agent; exhibits a greenhouse effect; stored in the gas–liquid two-phase state.

IV. Extinguishing Agent Storage Pressure (at 20°C)

Heptafluoropropane: Class I, 2.5 MPa; Class II, 4.2 MPa; Class III, 5.6 MPa.

IG541: Primary stage 15 MPa, secondary stage 20 MPa

High-pressure carbon dioxide: 5.7 MPa; low-pressure carbon dioxide: 2.2 MPa (at −18°C)

5. Maximum Working Pressure of the System (at 50°C)

Heptafluoropropane: Class I, 4.2 MPa; Class II, 6.7 MPa; Class III, 7.2 MPa.

IG541: Primary stage 17.2 MPa, secondary stage 23.2 MPa;

High-pressure carbon dioxide: 12.1 MPa; Low-pressure carbon dioxide: will not reach 50°C, so this item does not apply;

VI. System Pressure-Relief Actuation Pressure

Heptafluoropropane: Class I, 5.0 MPa; Class II, welded, 7.0 MPa; Class II, seamless, 8.4 MPa; Class III, 10.0 MPa.

IG541: Primary stage 20.7 MPa, secondary stage 27.6 MPa;

High-pressure carbon dioxide: 19 ± 0.95 MPa; low-pressure carbon dioxide: 2.38 ± 0.12 MPa;

VII. Maximum Filling Capacity per Unit Volume

Heptafluoropropane: Class I, 1.12 kg/L; Class II welded, 0.95 kg/L; Class II seamless, 1.12 kg/L; Class III, 1.08 kg/L.

IG541: Primary stage 0.21 kg/L, secondary stage 0.28 kg/L;

High-pressure carbon dioxide: 0.60 kg/L; low-pressure carbon dioxide filling coefficient ≤ 0.95 (volume ratio);

VIII. Nozzle Operating Pressure

Heptafluoropropane: Class I ≥ 0.6 MPa, Class II ≥ 0.7 MPa, Class III ≥ 0.8 MPa.

IG541: Class I ≥ 2.0 MPa, Class II ≥ 2.1 MPa

Carbon dioxide: High-pressure system ≥ 1.4 MPa, low-pressure system ≥ 1.0 MPa

9. Design Concentration for Fire Suppression or Design Concentration for Inerting

Heptafluoropropane: The design extinguishing concentration shall be no less than 1.3 times the extinguishing concentration, and the design inerting concentration shall be no less than 1.1 times the inerting concentration; the extinguishing and inerting concentrations can be determined from relevant tables. Special requirements for the design extinguishing concentration are as follows: ① For libraries, archives, document storage rooms, and cultural relic repositories, a concentration of 10% is recommended; ② For oil-immersed transformer rooms, switchgear rooms containing oil‑filled switches, and standby generator rooms, a concentration of 9% is recommended; ③ For telecommunications equipment rooms and electronic computer rooms, a concentration of 8% is recommended.

IG541: The design concentration for fire suppression shall be no less than 1.3 times the extinguishing concentration, and the design concentration for inerting shall be no less than 1.1 times the inerting concentration; the extinguishing and inerting concentrations can be determined from the relevant tables.

Carbon dioxide systems: For total flooding applications, the design concentration shall be no less than 1.7 times the extinguishing concentration and shall not be lower than 34%; whereas for localized application fire suppression systems, either the area method or the volume method may be used for design.

X. NOAEL Concentration and LOAEL Concentration

Heptafluoropropane: NOAEL concentration 9%, LOAEL concentration 10.5%

IG541: NOAEL concentration 43%, LOAEL concentration 52%

Carbon dioxide system: NOAEL concentration < 5%, LOAEL concentration < 10%

XI. Ambient Temperature

Heptafluoropropane and IG541 systems: the ambient temperature in the protected area shall not be lower than –10°C, and the ambient temperature of the storage unit shall be between –10°C and 50°C.

Carbon dioxide system: Ambient temperature in the protected area: −20°C to 100°C; ambient temperature of the storage unit: high-pressure system, 0°C to 49°C; low-pressure system, −23°C to 49°C.

XII. Limits on the Area and Volume of Protection Zones

Heptafluoropropane and IG‑541: ① For piped‑network systems, the area should not exceed 800 m², and the volume should not exceed 3,600 m³; ② For pre‑fabricated systems, the area should not exceed 500 m², and the volume should not exceed 1,600 m³.

Carbon dioxide system: No specific requirements.

13. Design Spray Duration of the Extinguishing Agent

Heptafluoropropane: ① For protected areas such as telecommunications equipment rooms and computer rooms, the discharge time shall not exceed 8 seconds; ② For other protected areas, the discharge time shall not exceed 10 seconds.

IG541: When the extinguishing agent is discharged to 95% of the design quantity, the discharge time shall not exceed 60 seconds and shall not be less than 48 seconds.

Carbon dioxide systems: ① For total flooding fire suppression systems, the discharge time shall not exceed 60 seconds; when extinguishing deep‑seated solid fires, the discharge time shall not exceed 7 minutes, and the carbon dioxide concentration shall reach 30% within the first 2 minutes. ② For localized application fire suppression systems, the discharge time shall not be less than 30 seconds; for fires involving liquids with a flash point lower than their boiling point and for combustible solids that can melt, the discharge time shall not be less than 1.5 minutes.

XIV. Fire Extinguishing Impregnation (Inhibition) Time

Heptafluoropropane: ① For fires involving solid surfaces such as wood, paper, and textiles, a discharge time of 20 minutes is recommended; ② For other solid-surface fires, a discharge time of 10 minutes is recommended; ③ For electrical equipment fires in telecommunications equipment rooms and computer rooms, a discharge time of 5 minutes is recommended; ④ For gas and liquid fires, the discharge time shall not be less than 1 minute.

IG541: ① For fires on solid surfaces such as wood, paper, and textiles, a discharge time of 20 minutes is recommended; ② For other solid-surface fires, a discharge time of 10 minutes is recommended; ③ For electrical equipment fires in telecommunications rooms and computer rooms, a discharge time of 10 minutes is recommended.

Carbon dioxide: Total flooding fire suppression systems for solid deep‑seated fires: ① For cotton, wool, textiles, paper, data storage rooms, and data printing equipment rooms, the duration is 20 minutes; ② For computer rooms, electrical switchgear and distribution rooms, cable rooms, and cable trenches, the duration is 10 minutes.

XV. Types of Systems

Heptafluoropropane: Classified by application type as total flooding fire suppression systems; classified by protected zone as unit‑independent systems and combined distribution systems; classified by piping configuration as piped systems and cabinet‑type (pipeless) pre‑assembled systems; and classified by pressurization method as internally pressurized systems and externally pressurized systems.

IG541: By application type, it is a total flooding fire suppression system; by protected zone, it is classified as either a unit‑independent system or a combined distribution system; by piping network configuration, it is a piped network system; and by pressure‑storage method, it is a self‑pressurized system.

Carbon dioxide: Classified by application method into total flooding and local application; by pressure into high-pressure systems and low-pressure systems; by protected zone or protected object into unit‑independent systems and combined distribution systems; by piping network configuration into piped systems and cabinet‑type (pipeless) pre‑assembled systems; and by pressurization method, all are self‑pressurized.