The heptafluoropropane fire suppression system is currently the most widely used and one of the most mature modern firefighting systems, both domestically and internationally.

1 Overview

The heptafluoropropane fire suppression system is currently the most widely used and one of the most mature modern firefighting technologies, both domestically and internationally. The heptafluoropropane (HFC‑227ea) extinguishing agent is colorless, odorless, non‑conductive, and leaves no secondary contamination; it has an ozone depletion potential (ODP) of zero, meeting stringent environmental standards. Its toxicological and adverse effects are even lower than those of halon agents, making it a highly desirable alternative to halons. HFC‑227ea offers superior fire‑extinguishing performance, causes no damage to equipment, provides excellent electrical insulation, and delivers rapid suppression. It can effectively extinguish Class A (surface‑burning), B, C fires, as well as electrical fires, and is suitable for areas frequently occupied by personnel. It is particularly well suited for fire protection in critical facilities such as computer rooms, libraries, telecommunications centers, underground structures, vaults containing valuable items, and electrical distribution rooms.

In recent years, while traditional heptafluoropropane fire‑extinguishing systems have been widely adopted in industrial and civil fire‑protection projects, they have also increasingly revealed numerous shortcomings. Chief among these is insufficient propellant‑gas supply, which limits the delivery distance of the extinguishing agent. Typically, internally pressurized systems with a storage pressure of 2.5 MPa can deliver the agent over approximately 30 m; those at 4.2 MPa over about 50 m; and those at 5.6 MPa over roughly 60 m. This limitation significantly constrains the applicability of heptafluoropropane systems, particularly when the protected zones are widely spaced, as it precludes the use of combined‑distribution configurations that could reduce installation costs. Moreover, design calculations often result in excessively large main‑line diameters for large‑space protection areas, sometimes necessitating the installation of two separate main lines. For many high‑rise buildings, large‑scale fire‑protection projects, or situations where multiple protection zones are involved—or where the protected areas are located far from the cylinder room—conventional stored‑pressure heptafluoropropane systems can no longer meet the required protection standards. To address these challenges, externally pressurized heptafluoropropane fire‑extinguishing systems have been developed.

 

2 System Composition and Operating Principle

2.1 System Composition

The externally pressurized heptafluoropropane fire suppression system primarily comprises: a extinguishing agent cylinder assembly, a propellant gas cylinder assembly, a driver gas cylinder assembly, a pressure-reducing device, a selection valve, a check valve, a manifold, a safety relief device, a low‑leakage high‑seal valve, a signal feedback device, an actuation mechanism, a frame, nozzles, piping fittings, and a fire alarm and control system. Depending on the application requirements, it can be configured as either a unitary independent system or a combined distribution system. It is capable of providing total flooding protection for a single zone or multiple zones only.

1. Collector pipe 2. Check valve (for extinguishing agent delivery pipeline) 3. Extinguishing agent cylinder rack 4. Initiation pipeline 5. Connecting pipe 6. Pressure-reducing device 7. Liquid-level measuring device 8. Extinguishing agent cylinder assembly 9. Propellant gas cylinder assembly 10. Propellant gas cylinder rack 11. Propellant gas cylinder assembly 12. Low-leakage, high-seal valve 13. Electromagnetic actuator 14. Selective valve 15. Signal feedback device 16. Check valve (for propellant gas pipeline) 17. Safety relief device 18. Automatic fire alarm and gas‑extinguishing controller 19. Control wiring 20. Manual start control box 21. Gas‑release indicator light 22. Audible and visual alarm 23. Nozzle 24. Fire detector 25. Extinguishing agent delivery pipeline

2.1.2 Unit-Independent System

1. Collector pipe 2. Check valve (for extinguishing agent delivery pipeline) 3. Extinguishing agent cylinder rack 4. Initiation pipeline 5. Connecting pipe 6. Pressure-reducing device 7. Liquid-level measuring device 8. Extinguishing agent cylinder assembly 9. Propellant gas cylinder assembly 10. Actuating gas cylinder assembly 11. Low-leakage, high-seal valve 12. Electromagnetic actuator 13. Signal feedback device 14. Safety relief device 15. Automatic fire alarm and gas‑extinguishing controller 16. Control wiring 17. Manual start control box 18. Gas‑release indicator light 19. Audible‑visual alarm 20. Extinguishing agent delivery pipeline 21. Nozzle 22. Fire detector

 

2.2 Operating Principle

Compared with the conventional internally pressurized heptafluoropropane fire‑extinguishing system, the most significant difference of the externally pressurized system is that it stores the heptafluoropropane extinguishing agent and the propellant gas in separate containers. During discharge, the propellant gas is charged into the extinguishing‑agent storage cylinder, rapidly increasing the pressure inside the agent container and driving the agent at high velocity through the piping network to achieve fire suppression. The externally pressurized heptafluoropropane system offers three activation modes—automatic, electrically‑controlled manual, and mechanically‑emergency manual—identical to those of the internally pressurized system; further details will not be repeated here.

 

3 Product Features

Compared with internally pressurized heptafluoropropane fire suppression systems, externally pressurized heptafluoropropane fire suppression systems have the following characteristics:

3.1 Heptafluoropropane fire‑extinguishing agent has a long delivery distance, making it suitable for protecting remote and large‑space protected areas. In internally pressurized systems, insufficient power‑gas supply limits the delivery distance: for systems with an internal storage pressure of 2.5 MPa, the pipeline delivery distance is approximately 30 m; for 4.2 MPa systems, about 50 m; and for 5.6 MPa systems, roughly 60 m. Externally pressurized systems, equipped with a separate power‑gas cylinder bank, provide ample driving gas and power, enabling much longer delivery distances. Extensive testing has demonstrated that externally pressurized heptafluoropropane systems can achieve delivery distances exceeding 200 m.

3.2 The extinguishing agent has a high filling density, resulting in a reduced number of extinguishing‑agent cylinders required. In internally pressurized systems, nitrogen is used to boost the pressure within the extinguishing‑agent cylinders; under certain ambient temperatures, the storage pressure can rise sharply, posing a serious safety risk to the vessels, and thus limiting the allowable filling density. According to the national standard GB 25975‑2010 “Gas Fire‑Extinguishing Systems and Components,” the specified filling densities for internally pressurized heptafluoropropane fire‑extinguishing systems are as follows: for 2.5 MPa systems, no more than 1,120 kg/m³ (steel welded cylinders); for 4.2 MPa systems, no more than 950 kg/m³ (steel welded cylinders); and for 5.6 MPa systems, no more than 1,080 kg/m³ (steel seamless cylinders). By contrast, externally pressurized systems store the boosting nitrogen separately in a dedicated motive‑gas cylinder bank. Under normal operating conditions, the pressure in the extinguishing‑agent cylinders equals only the saturated vapor pressure of the extinguishing agent, and the gas‑phase space above the extinguishing‑agent cylinders need only occupy about 10% of the total volume of the agent cylinders (as stipulated in Clause 3 of Section 4.1.1 of CECS 386:2014). Consequently, the filling density of the vessel can be significantly increased—exceeding 1.3 times that of internally pressurized systems. Typically, domestic manufacturers set the maximum filling density at 1,250 kg/m³, which also leads to a substantial reduction in the number of extinguishing‑agent cylinders required.

3.3 The system’s piping exhibits superior flow characteristics, allowing for a reduction in pipe diameter and lower installation costs. In an internally pressurized system, nitrogen and the heptafluoropropane extinguishing agent are stored together under pressure, inevitably leading to some of the nitrogen dissolving into the liquid heptafluoropropane. During discharge, as the system pressure declines, the dissolved nitrogen is released, forming gas pockets and inducing two-phase flow in the delivery lines, which directly degrades the extinguishing agent’s flow performance. By contrast, an externally pressurized system stores the extinguishing agent and nitrogen separately in distinct vessels, eliminating the phenomenon of nitrogen dissolution in the agent. During discharge, the extinguishing agent flows as a single‑phase liquid through the piping, thereby preventing gas pockets and two‑phase flow. This results in improved flow characteristics, enabling the use of smaller‑diameter pipes to convey greater volumes of extinguishing agent, and reducing both the cost of the piping network and overall installation expenses.

3.4 A higher nozzle inlet pressure results in better atomization of the extinguishing agent, shorter discharge time, and improved fire‑extinguishing performance. In externally pressurized systems, by adjusting the pressure and optimizing the nitrogen charge, the nozzle inlet pressure can be increased, thereby enhancing the atomization of the extinguishing agent and boosting its fire‑extinguishing effectiveness. This also shortens the discharge duration, enabling rapid fire suppression and improving overall extinguishing efficiency.

3.5 Applicable to both new project construction and the retrofitting of existing facilities. In particular, when upgrading legacy halon‑based gas systems such as the 1301 system, an externally stored‑pressure system can directly leverage the existing piping network, thereby significantly reducing construction costs and time.

However, the internally pressurized system is limited by the transmission distance and cannot directly utilize the existing 1301 system’s piping network for the project’s retrofit.

 

4. Prospects for Product Application and Existing Shortcomings

4.1 Product Application Prospects

Since its introduction in the 1990s, heptafluoropropane fire‑extinguishing agent has been widely adopted both domestically and internationally, thanks to its excellent extinguishing performance, superior environmental compatibility, and relatively low storage pressure. The externally pressurized fire‑extinguishing system further addresses the limitations of conventional systems—namely, short pipeline transport distances and excessively large pipe diameters—while reducing the number of extinguishing‑agent cylinders and minimizing the floor space required between cylinders. It is energy‑efficient, highly effective, cost‑effective, and environmentally friendly, aligning with national policies on energy conservation and environmental protection. With societal progress and growing public emphasis on fire safety, its applications are expected to become increasingly widespread.

4.2 Existing Shortcomings

Because the externally pressurized heptafluoropropane fire‑extinguishing system stores a relatively large quantity of extinguishing agent in each individual cylinder, it can result in an excessively high discharge concentration when used to protect smaller protected zones within the same combined distribution system. When the extinguishing concentration in a protected zone exceeds 10.5%, it may pose a health risk to personnel and also represents a significant waste. Therefore, externally pressurized combined distribution systems are no longer suitable for protecting very small zones; for such small areas, it is recommended to employ cabinet‑type heptafluoropropane gas fire‑extinguishing units. The costs saved on initiating devices, selection valves, piping networks, and installation are comparable to the purchase price of a cabinet‑type heptafluoropropane gas fire‑extinguishing unit, so there is no net increase in overall project costs.

 

5 Product Model and Main Specifications

The externally stored‑pressure heptafluoropropane fire‑extinguishing system of Guangzhou Xinlin Fire Equipment Co., Ltd. is designed, manufactured, and inspected in accordance with the enterprise standard Q/LDHX 002-2020 “Externally Stored‑Pressure Heptafluoropropane Fire‑Extinguishing Systems and Components,” as well as the national and industry standards GB 25972-2010 “Gas Fire‑Extinguishing Systems and Components,” GB 50370-2005 “Code for Design of Gas Fire‑Extinguishing Systems,” and CECS 386:2014 “Technical Specification for Externally Stored‑Pressure Heptafluoropropane Fire‑Extinguishing Systems.” The system features complete and accurate design parameters, comprehensive functionality, reliable and precise operation, and excellent sealing performance. The product models and key technical specifications of our externally stored‑pressure heptafluoropropane fire‑extinguishing systems are listed in the table below.

Product model

20℃ Nominal working pressure of the device MPa

50℃ Maximum working pressure at the time MPa

At 0°C Minimum working pressure MPa

Fire extinguishing agent cylinder volume (L)

Maximum filling density of the extinguishing agent (kgL)

Volume of the propellant gas cylinder bank (L)

Storage pressure of the propellant gas cylinder bank MPa

Drive Gas Cylinder Bank Volume (L)

Stored pressure of the driver gas cylinder bank MPa

Using the annular wall temperature (°C)

Iodine injection time (5)

System startup power supply

Startup method

QMQ42/90W

4.2

53

3.6

90

1.25

70

13.5

4

6.0

0-50

≤10

AC220 DC 24±3V 1.1A

Automatic; electric manual; Mechanical emergency manual

QMQ4.2/120W

120

QMQ4.2/150W

150

QMQ42/180W

180