In-Cabinet Gaseous Fire Suppression
Systems

Design, System Selection and Key Considerations

TÜYAK Fire Engineering Journal  |  2026

Muhammed ÖZÇELİK
Business Development Manager | Rotarex Firetec

Introduction

In this article, I aim to provide a clear and practical reference on the types, design criteria, system selection principles, and maintenance requirements of in-cabinet gaseous fire suppression systems, which provide localized detection and suppression in electrical cabinets, industrial machinery, fume cupboards, and similar enclosed spaces where there is a high fire risk or where firefighting intervention may be difficult.

Before beginning, I would like to thank TÜYAK, which has contributed to shaping our professional and cultural memory since 1992 and has helped preserve and develop our collective knowledge around shared values, as well as Özlem Karadal, who provided the opportunity for us to create this resource.

Figure 1: Electrical cabinet room in an industrial facility

Why an In-Cabinet Fire Suppression System?

Research and statistics from various countries around the world demonstrate that electrical fires continue to be among the most common causes of fires in residential, commercial, and industrial facilities. According to data from the U.S. Fire Administration (USFA), approximately 7,400 fires caused by electrical malfunctions occurred in nonresidential buildings in 2023, resulting in USD 354 million in property losses. In the industrial sector, electrical fires account for approximately 22% of nonresidential building fires.

It should be noted that detailed institutional statistics identifying the specific causes of electrical fires in Türkiye are not sufficiently accessible. Nevertheless, statistics from the United States and European countries with established databases consistently demonstrate the significance of electrical fires.

When a fire occurs inside a largely enclosed space such as an electrical cabinet, fume cupboard, or industrial machine, the time required for the general fire detection and suppression systems protecting the surrounding area to activate can significantly restrict intervention opportunities. During this period, the fire may grow rapidly.

The fundamental objective of an in-cabinet system is simple: Detect and suppress the fire at its source, at the moment it starts.

In recent years, relevant ministries, consultants, and end users have significantly increased their demand for in-cabinet fire detection and suppression systems. However, an important issue associated with this growing demand should not be overlooked: in-cabinet suppression applications that are not based on any international standard are becoming increasingly common in industrial facilities due to their low cost. Some are even offered through e-commerce platforms with technical descriptions that have no recognized validity.

Furthermore, even when approved systems are used, the number of installations implemented outside their approved design limitations is considerably higher than might be expected. One of the primary objectives of this article is therefore to explain what designers and end users should consider when selecting a correct, reliable, and properly approved system.

Applicable Standards

In-cabinet gaseous fire suppression systems are designed internationally within the framework of the following principal standards and are approved by independent testing organizations:

• LPS 1666 – Published by the LPCB (Loss Prevention Certification Board), this standard defines performance testing and approval requirements specifically for Direct Low Pressure (DLP) local application systems. It is a primary reference standard for in-cabinet systems using FK-5-1-12 and HFC-227ea agents.
• NFPA 2001 – Standard on Clean Agent Fire Extinguishing Systems (USA).
• UL 2166 / FM 5600 – These standards from independent testing and approval organizations UL and FM govern independent testing and listing procedures for total flooding systems as well as Indirect Low Pressure (ILP) in-cabinet suppression systems.
• VdS 2093en – One of Europe's principal standards for the design and installation of CO₂ fire extinguishing systems.

At this point, a critical distinction must be emphasized:

A manufacturer's “declaration of compliance with a standard” and a system-level approval issued by an independent testing organization are fundamentally different concepts.

Certificates of conformity based solely on a manufacturer's declaration cannot substitute for independent performance testing. A genuinely reliable system should consist of products that have undergone system-level independent testing by organizations such as UL, FM, LPCB, VdS, or CNPP.

The fact that only a few individual components are certified does not mean that the complete system itself is reliable or approved.

Basic Operating Principle: Pneumatic Detection Tubing

The most characteristic and distinctive component of these systems is pneumatic detection tubing.

This red polymer tube, typically 6 mm in outside diameter and pressurized with nitrogen gas (N₂) or air, functions both as a continuous linear heat detector and as a triggering mechanism for the release of the extinguishing agent. The tubing is installed as close as practically possible to the components inside the cabinet. Depending on the tubing type selected, it bursts when exposed to the specified temperature range. When the tubing bursts, system pressure drops. This pressure drop activates the valve mechanism, which in turn releases the extinguishing agent.

The detection tubing must be UL Listed or independently approved specifically for fire protection applications. There are products on the market described simply as “heat-sensitive tubing” that have no independent approval and rely solely on manufacturers' declarations. Systems incorporating such products cannot be regarded as reliable.

For cabinets where detection tubing cannot be installed, point-type smoke and heat detectors may be used. In applications requiring a higher level of protection, air-sampling detection systems may also be considered. In such cases, the cylinder valves must be capable of electrical activation.

System Types and Selection Criteria

In-cabinet gaseous fire suppression systems can be divided into four principal types.

System selection is primarily based on three parameters:

1. Cabinet volume
2. Enclosure integrity
3. Size and quantity of openings that cannot be closed

Low-pressure systems use FK-5-1-12 or HFC-227ea as the extinguishing agent, while high-pressure systems use carbon dioxide (CO₂).

In very specific applications, inert gases may also be selected as the extinguishing agent for high-pressure systems. However, due to storage space requirements and the presence of openings that cannot be closed, the use of inert gases is extremely limited.

1. Direct Low Pressure System – DLP (FK-5-1-12 ve HFC-227ea)

The DLP system is the most commonly used type of in-cabinet suppression system.

Its operating principle is very straightforward: the red detection tubing functions directly as the extinguishing discharge line, meaning that no additional piping or nozzles are required. When the tubing bursts at the fire location, the FK-5-1-12 extinguishing agent is discharged directly from that point.

It is a pre-engineered system that does not require hydraulic flow calculations.

Main Parameters

• Maximum cabinet volume: 2 m³ under LPS 1666
• Maximum tubing length: 10 m under LPS 1666
• Operating pressure: 16.5 bar @ 21 °C
• Discharge time: 10 seconds
• Approval: LPCB
• Small ventilation openings may be permitted according to manufacturers' test results.

Figure 4: Electrical cabinet equipped with a DLP system

2. Indirect Low Pressure System – ILP (FK-5-1-12 ve HFC-227ea)

In an ILP system, the detection tubing functions only as the triggering mechanism. The extinguishing agent is discharged into the cabinet through stainless-steel piping and nozzles.By strategically positioning the nozzles, a homogeneous extinguishing concentration can be achieved in large-volume and multi-compartment cabinets. The system incorporates a manual release device, and a solenoid actuator is also available as an option.

Main Parameters

• Maximum cabinet volume: Varies according to manufacturer capacity; however, applications in cabinets larger than 2 m³ are possible.
• Maximum tubing length: Since the tubing is used only for detection, substantially more flexible limits than DLP systems may be possible, e.g. 35 m.
• Approvals: UL, FM
• Cabinets or protected spaces must be sufficiently sealed in accordance with UL and FM test criteria.

Figure 5: Electrical cabinet equipped with a ILP system

3. Direct High Pressure System – DHP (CO₂)

The DHP system uses CO₂ as the extinguishing agent, while the detection tubing functions both as the detector and the discharge line. Because CO₂ is stored at high pressure (60 bar @ 20 °C), DHP systems offer advantages over DLP systems in terms of tubing length and maximum protected volume.

They are particularly advantageous for cabinets where nozzle holes are undesirable and for cabinets with larger ventilation openings than those typically permitted for DLP systems.

Main Parameters

• Maximum cabinet volume: Varies according to manufacturers' test criteria, but applications in cabinets larger than 2 m³ are possible.
• Maximum tubing length: Due to the operating pressure of CO₂, more flexible limits than DLP systems are possible, e.g. 25 m.
• Maximum CO₂ capacity: Depends on the manufacturer's valve technology; products tested with capacities of up to 5 kg are available.
• Operating pressure: 60 bar @ 20 °C
• Discharge time: 60 seconds
• Design standard: VdS 2093en

Figure 6: Small electrical cabinet equipped with a CO₂ DHP system

4. İndirekt Yüksek Basınçlı Sistem – IHP (CO₂)

IHP sistemi, CO₂ kullanılan en kapsamlı pano içi söndürme çözümüdür. Büyük hacimli, birden fazla bölmesi olan ve bölmeler arası geçişlerin bulunduğu panolarda tercih edilir. Paslanmaz çelik boru hattı, esnek bağlantı hortumları ve çelik nozullardan oluşan dağıtım sistemi ile geniş alanlarda homojen söndürme sağlanır. CO₂ sistemlerinde, söndürme ajanının fiziksel yapısı gereği manometre kullanılamaz. Bunun yerine, sistemin aktif olarak ağırlık ölçümünü sağlayan dijital ölçüm çözümleri mevcuttur; bu sayede silindir ağırlığı gerçek zamanlı olarak uzaktan izlenebilmektedir.

• Maksimum pano hacmi: Üreticilerin çözümlerine göre çok daha büyük uygulama alanlarında kullanılabilir, 40 m³ vb.
• Maksimum tubing uzunluğu: Tubing sadece algılama işlevi için kullanıldığından DLP sistemlere göre çok daha esnek limitler belirlenebilir, 100 m vb.
• Maksimum CO₂ kapasitesi: Üreticilerin testlerine göre çok daha yüksek ağırlıkta çözümler sunmak mümkündür, 50 kg vb.
• Çalışma basıncı: 60 bar @ 20 °C
• Tasarım standardı: VdS 2093en

Görsel 7: Örnek IHP çok bölmeli pano uygulaması (Dijital izleme sistemi ile)

Silindir Setleri

Sistemlerde kullanılan basınçlı silindir setleri TPED (Taşınabilir Basınçlı Ekipman Direktifi) uyumlu, CE işaretli ve kırmızı kaplamalı çelik konstrüksiyondan oluşmalıdır. Üreticiler hem FK-5-1-12 sistemlerinde hem de CO₂ sistemlerinde ise uygulama büyüklüğüne göre geniş bir kapasite yelpazesi sunmaktadır.
 

Görsel 8: Örnek FK-5-1-12 silindir setleri

Görsel 9: Örnek CO₂ silindir setleri

Sistem Seçim Tablosu

Aşağıdaki tablo, mühendislerin sistem seçiminde başvurabileceği temel kriterleri özetlemektedir:

⁽¹⁾ FK-5-1-12 yerine HFC-227ea da kullanılabilir ancak son yasal kısıtlamalar sebebiyle yalnızca FK-5-1-12 belirtilmiştir.

⁽²⁾ Spesifik bir üreticinin limitleri doğrultusunda okuyucunun zihninde fikir oluşması açısından aralık belirtilmiştir, her üreticinin test ve limitleri farklılık gösterebilir.

⁽³⁾ LPS 1666 kapsamında izin verilen çok küçük açıklıklar mevcut olabilir, ilgili üreticiye danışılmalıdır.
⁽⁴⁾ Kapatılamayan açıklıklar varsa VdS 2093 hesaplarına dahil edilmelidir. Sızdırmazlık gerekmez tabirinin her zaman limitli olduğu unutulmamalıdır. Tasarım esnasında detaylı limitler için üreticilere başvurulmalıdır.

Tasarım Kriterleri ve Dikkat Edilmesi Gereken Hususlar

Tubing Güzergahı ve Yerleşimi

Algılama tubingi, yangın riskinin en yüksek olduğu noktalara — sigorta blokları, güç devreleri, kablo bağlantı noktaları — olabildiğince yakın geçirilmelidir. Doğru güzergah planlaması, hem erken algılamayı hem de etkin söndürmeyi doğrudan etkiler. Tubing pano içindeki bileşenlere sabitleme aparatlarıyla güvenli biçimde tutturulmalı; keskin kenarlara karşı panel geçiş koruyucuları kullanılmalıdır.

Görsel 10: Panel geçiş koruyucu fitting

Havalandırma

Boşaltma başladığında paneldeki tüm havalandırma cihazları kapatılmalıdır. Bu işlem basınç anahtarı vasıtasıyla otomatik olarak gerçekleştirilmelidir. Havalandırmaların açık kalması söndürücü ajan konsantrasyonunu düşürerek söndürmenin başarısız olmasına neden olabilir. Yeniden tutuşmaları önlemek için güç kaynakları da mümkünse boşalma sırasında kesilmelidir.

Manuel Başlatma ve İzleme

ILP ve IHP sistemlerinde manuel boşaltma butonu kullanılabilir. Bu sayede ilgili personel olası bir durumda sistemi elle devreye alabilir. Tüm sistem tiplerinde basınç anahtarı entegrasyonu sağlanmalı; boşalma anında merkezi adresli yangın alarm sistemine veya lokal sesli-ışıklı uyarı cihazlarına sinyal iletilmelidir.

Dolumlar

Sistemlerin ilk dolumu üreticinin kendi tesisinde veya yetkili dolum istasyonunda yapılmalıdır. Her silindir için dolum sertifikası — seri numarası, ajan miktarı, dolum tarihi ve dolum yeri bilgilerini içerecek şekilde — yetkili firma tarafından imzalı sunulmalıdır. Sistemin boşalması durumunda 48 saat içinde ilgili dolum istasyonuyla iletişime geçilmelidir.

Applications

In-cabinet gaseous fire suppression systems are not limited to electrical cabinets.

Typical applications include:

• Electrical cabinets
• Fume cupboards / laboratory cabinets
• CNC lathes and machinery

      Figure 13: Electrical cabinet                   Figure 14: Fume cupboard /                  Figure 15: CNC lathe                               
laboratory cabinet
   

Maintenance

The effectiveness of a fire suppression system depends not only on correct design but also on regular maintenance. The following simplified maintenance schedule, based on manufacturers' manuals, provides readers with an overview of the fundamental maintenance requirements:

Procurement and Technical Evaluation Guide

End users, consultants, and project designers should request the following documents from suppliers and evaluate the following criteria.

Mandatory Documentation

• System-level independent approval certificate: UL, FM, LPCB, VdS, CNPP, or a system certificate issued by another independent and reputable testing organization. Certification of individual components alone is not sufficient.
• Pre-engineered system design sheets and a manufacturer-approved preliminary calculation report.
• Technical data sheets and applicable CE and TPED documentation for all components.
• Independent UL/FM approval documentation for the chemical extinguishing agent (FK-5-1-12).
• Manufacturer-authorized partner certificate for the company performing the installation.
• Current manufacturer-issued training certificates for the installation team, preferably issued within the last three years.
• Filling certificate containing the cylinder serial number, quantity of extinguishing agent, filling date, and filling location.
• Availability of a filling facility within Türkiye and the relevant filling station's contact information.

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Equipment Quality Criteria

• Detection tubing should be UL Listed or independently approved by a reputable organization specifically for use in fire protection applications.
• The cylinder valve should comply with CE and TPED requirements.
• Piping and fittings should be manufactured from stainless steel, particularly to ensure long-term durability.
• All system components should be supplied by a single manufacturer.
• The pressure switch should comply with the applicable RoHS and LVD requirements.

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Technical Warnings

• System design should only be carried out by the manufacturer or a company authorized by the manufacturer.
• For CO₂ systems, the volumetric concentration calculation for occupied spaces should be performed with consideration of the 5% LOAEL limit. Following system discharge, the protected space must always be adequately ventilated, regardless of the concentration level.
• If the permitted opening limit or maximum volume limit for a DLP system is exceeded, a DHP or IHP system should be selected.
• For ILP systems, the cabinet must be fully sealed. Otherwise, IHP or DHP should be considered.
• After installation, the points where the tubing line connects to the cylinder should either be sealed in the open position or capable of being remotely monitored.
• Following installation of the system, personnel should receive operation and maintenance training, and the relevant training records should be retained.

Conclusion

In-cabinet gaseous fire suppression systems provide highly effective solutions for suppressing fires at their source and at the earliest possible stage.

Correct system selection depends on:

• Cabinet volume
• Enclosure integrity
• Size and quantity of openings

FK-5-1-12-based systems provide environmentally preferable, residue-free solutions suitable for use in occupied areas, while CO₂-based systems can provide cost advantages for larger-volume applications and applications with larger openings. However, the most critical consideration is this:

System effectiveness depends not only on correct design, but also on system-level approvals from independent testing organizations, qualified installation, and regular maintenance.

Selecting products that lack recognized standards approval or have not undergone independent testing may provide a short-term cost advantage, but it can create risks to life safety and property protection that far exceed any initial savings. Developing stronger awareness of these issues throughout our industry is vital to enabling both engineers and end users to make informed decisions. I hope this article makes even a small contribution toward achieving that objective.

References

1. U.S. Fire Administration (USFA). (2023). Nonresidential Building Electrical Malfunction Fire Trends 2014–2023. Federal Emergency Management Agency.
2. Rimkus Consulting Group. (2026, January). Industrial Electrical Fires: Causes, Signs, and Investigation Methods.
3. Rotarex Firetec S.A. (2026). FireDETEC® Direct Low Pressure (DLP) System for FK-5-1-12 – Instruction Manual B0700 EN (Index b, Rev. 2026/03/23).
4. Rotarex Firetec S.A. & Rotarex North America Inc. (2026). FireDETEC® Indirect Low Pressure (ILP) Total Flooding System for FK-5-1-12 – Instruction Manual B0701 EN (Index d, Rev. 2026/01/28).
5. Rotarex Firetec S.A. (2026). FireDETEC® Direct CO₂-System – Instruction Manual B0750 EN (Index h, Rev. 2026/05/20).
6. Rotarex Firetec S.A. & Rotarex North America Inc. (2026). FireDETEC® Indirect CO₂-System – Instruction Manual B0750 EN (Index b, Rev. 2026/05/22).
7. LPCB. (2017). LPS 1666 Issue 1: Requirements and Test Procedures for the LPCB Approval of Direct Low Pressure (DLP) Application Fixed Fire Suppression Systems.
8. NFPA. (2025). NFPA 2001: Standard on Clean Agent Fire Extinguishing Systems. National Fire Protection Association.
9. VdS Schadenverhütung. (2022). VdS 2093en: CO₂ Fire Extinguishing Systems – Planning and Installation.
10. FM Approvals. (2023). FM 5600: Examination Standard for Clean Agent Extinguishing Systems.
11. UL Standards. (2021). UL 2166: Standard for Safety – Halocarbon Clean Agent Extinguishing Systems Units.

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