An article detailing smoke duct fire prevention technology

With the government authorities in accordance with the 'building smoke and exhaust system technical standards' GB 51251-2017 specification of smoke and exhaust fire-resistant duct fire resistance limit design and implementation of further strict requirements, the current smoke and exhaust fire-resistant duct application form of good and bad, this paper is based on the smoke and exhaust duct engineering practice related to the thinking of the current market use of fireproof coatings, rock wool, the external cladding fireproofing materials, the integration of the air duct to analyze.

First of all, when steel plate ducts are used, whether or not fireproof coatings can be used as fire protection measures is an issue that has been highly controversial!


Normative adaptation is controversial:
1. The product standard of fireproof coating 'Steel Structure Fireproof Coating' (GB14907-2018) is to use Q235 steel as the test piece substrate (6.3.1), and apply fireproof coating on the bare substrate after thoroughly removing rust.

2. The Technical Code for Fire Protection of Building Steel Structures (GB51249-2017) mainly focuses on structural steel, which refers to low carbon structural steel and low alloy structural steel with a yield platform applied in large quantities in steel structure projects, including Q235 steel, Q345 steel, Q390 steel and Q420 steel.

3, smoke pipe is usually galvanized steel, the contact surface of the fireproof coating is galvanized layer, which is different from the bonded base layer mentioned above, and it is controversial whether it can be adapted to the above specifications.


Difficulty of actual construction and on-site protection:

1. High construction difficulty:

The adhesive force of fireproof coating is limited, and the boards coated with fireproof coating are easily damaged by collision and other external forces, so it is impossible to apply coating before installation, and it is only possible to apply coating after installation, and it is difficult to apply coating in place according to the specification under the influence of other kinds of building components, such as process piping, decoration materials, and so on, especially for the air ducts in wells or suspended ceilings, and basically do not have the conditions for construction.

2. High difficulty of on-site protection:

Anti-smoke pipe is usually mixed between pipes, materials and components of various professions such as water and electricity, air conditioning, decoration, etc., and it is easy to be damaged by other professions after the fireproof coating has been applied, which is almost unavoidable no matter whether it is at the stage of on-site construction, or in the future operation and maintenance!


Operational impacts are high and maintenance is difficult:

The commissioning, acceptance and subsequent regular maintenance of the smoke prevention and exhaust system require frequent startup of the smoke prevention and exhaust fan, the specification requires the fan to be located in the concrete or steel foundation, and should not be equipped with vibration damping devices (6.5.3), the fan startup, the system will produce a large vibration, which is bound to adversely affect the adhesion performance of the fireproofing coatings.


Fireproof coating volatilizes toxic and harmful gases at high temperatures

To summarize, fireproof coating should not be used as a fire protection measure when steel plate ducts are used for smoke prevention and exhaust ducts. The landmark requirement of external fireproof coating for metal ducts cannot be adopted:

(1) Interpretation of some technical issues in Yunnan Province regarding the Technical Standard for Building Smoke Prevention and Exhaust System (2019.05.17) Article 16: Spraying (coating) fireproof coating - can be used for steel structure warehouse, but should not be used for civil buildings and factories, the reasons are mainly:

First, the fireproof coating volatilizes toxic and harmful gases at high temperature;

Second, the fireproof coating expands and deforms under high temperature, which may hinder the normal action of the actuators such as dampers.

(2) In Suzhou Wujiang District Housing and Urban-Rural Development Bureau document [Wuzhujian Consumption (2020) No. 18], 'Some Guidelines on Common Problems in Fire Protection Design of Construction Projects', (14) Fireproof coating shall not be applied as a measure to meet the fire resistance limit of the air supply and smoke exhaust ducts.

(3) Xuzhou City Refrigeration Society Xuzhou City Civil Engineering Society HVAC Specialized Committee 'Building Smoke Prevention and Exhaust System Technical Standard' GB51251-2017 Xuzhou Regional Technical Seminar for Examiners (Version 2.0.2) Article 7: Spraying (coating) fireproofing coatings - can be used in steel structure warehouses, but should not be used in civil buildings and factories, the reason is mainly:

First,Fireproof coating volatilizes toxic and harmful gases at high temperature;

Second,  Fireproof coating expands and deforms under high temperature, which may hinder the normal operation of the actuators such as dampers.

Second, we analyze why centrifugal glass wool is not recommended for use in smoke evacuation ducts fire resistance limit wording.


Is glass wool suitable for fireproof cladding of smoke exhaust ducts?

Glass wool is a common insulation material, widely used in building insulation and thermal insulation. So can glass wool be applied to the fireproof cladding of smoke exhaust ducts?

According to the current GB/T13350-2017 'insulation with glass wool and its products' for the definition of glass wool products: normal glass wool productnormal glass wool product for working temperature is not higher than 250 ℃ glass wool products.

High temperature glass wool product glass wool product used in high temperature can be used in high temperature working conditions (hot surface temperature greater than 250 degrees Celsius) and through the highest use temperature assessment.

High temperature glass wool product used in high temperature working conditions (hot surface temperature greater than 250 degrees Celsius), and through the highest use temperature assessment of glass wool products. So what is the maximum service temperature for high temperature glass wool products? According to the world's several well-known glass wool manufacturer's website, Owens Corning OWENS CORNING, Jiesman Johns Manville its announced high temperature insulation glass wool products are in the highest use temperature of 300 ~ 500 degrees Celsius:

Glass wool materials and products, why its use of temperature range, especially high temperature resistance are in the range of 300-500 degrees Celsius, it is difficult to break through? This is due to the material composition of glass wool products and production processes decided.

Glass wool is a molten glass fibrillated and thermosetting resin-based binder processed into products, its main component is glass fiber. Glass fiber itself is non-combustible, and has a certain high temperature resistance.

But the glass fiber made of glass wool products must be added to the resin binder, play a role in bonding glass fibers and maintain structural support.

In the event of high temperatures (usually 300-500 degrees Celsius), the resin binder will be carbonized and melted, the glass wool will lose the structural support, which is the glass wool can not withstand high temperatures of more than 500 degrees Celsius, the key factor.


The low melting point of glass wool does not meet the requirements of fire protection

According to the following figure, the temperature rise curve of the national standard GB9978 building fire standard is also the temperature rise curve used in GB17428-2009 ventilation duct fire resistance test. The temperature rises very rapidly at the beginning of the fire, reaching 842 degrees Celsius in 0.5 hours and 945 degrees Celsius in 1.0 hour.


Usually the melting point of glass wool is about 565 degrees Celsius, through the fire standard temperature rise curve fitting: when the fire occurs in about 6 minutes, the glass wool will melt and sinter. When the insulation material melting and sintering, its structure, size, color and other huge changes. Its physical properties such as thermal conductivity, thermal resistance, etc. will change abruptly.


Duct insulation materials to be used above the melting point of 800 ℃ non-combustible materials

Refer to Article 4.3.10 of the Shanghai Landmark Smoke Prevention and Exhaustion Guidelines, which states that duct insulation materials should be non-combustible materials with a melting point of 800℃ or above:


4.3.10 In order to prevent the high temperature of the smoke exhaust pipe itself from igniting the combustible materials in the ceiling, the provisions of this article stipulate that the smoke exhaust ducts installed in the ceiling have thermal insulation measures. According to the requirements of this standard, smoke exhaust pipe at least half an hour of fire-resistant limit requirements, and combustibles with a distance of not less than 150mm; then we need to check the smoke exhaust pipe insulation thickness, the general requirement is not less than 35mm thick rock wool insulation, or other heat-resistant 800 ℃ temperature above the insulation material.


Centrifugal glass wool products are not recommended

Centrifugal glass surface manufacturers in the current market, why can get a qualified type inspection report? Reason many manufacturers of centrifugal glass wool test report, galvanized iron and glass wool between the large dose of high temperature adhesive coating.

Therefore, it is not recommended to use centrifugal glass wool products as fire-resistant limit fireproof cladding material for air ducts.

Thirdly, we analyze the analysis of technical solutions about fireproof and heat-insulating materials wrapped around the outside of tin air ducts.


Galvanized iron + rock wool + fireproof board made on site


Galvanized iron + rock wool + fire prevention board belongs to the original traditional way of fire duct production, as shown in Figure 1. Early through the firewall or partition wall has been used, galvanized iron duct production, iron outside the paste rock wool, rock wool exterior and then laying fire prevention board.

The body of all on-site production, the site workload is huge; rock wool thickness of 50mm, fire prevention board for 8-12mm, occupying a large space, the structure is not solid; due to on-site production, there may be safety hazards; fire prevention board exposed, not adapt to the humid environment; due to all on-site production, the assembly rate is very low, the high cost of labor, the cost is high.


Galvanized iron + thermal insulation adhesive + flexible high-temperature centrifugal cotton

This way of galvanized iron made on site, iron outside the high-temperature centrifugal cotton, centrifugal cotton thickness of 50mm, occupying a large space, the site of the workload, centrifugal glass wool outside and then wrapped in aluminum foil veneer, the production method is similar to the air-conditioning ducts + centrifugal glass wool + aluminum foil.

If set in the underground garage and other exposed space, the aluminum foil is easily damaged, resulting in exposed heat insulation layer, poor durability, and affects the appearance, the production process of artificial workload.

The product test report shows that the weight of the specimen is obviously too heavy unreasonable, for example, 1.0mm thick steel plate is 8kg / ㎡, 50mm thick glass wool weight 2.5-4kg / ㎡, why the specimen in the test report on the weight of up to 30kg / ㎡? One can't help but question whether so much heat-insulating adhesive is also applied during on-site production, and whether it can pass the re-inspection.











Double-sided color steel composite duct

Can only factory assembly finished products, can not site processing, can not be flexible to face the site changes, color steel plate thickness of 0.3-0.5mm or so, the strength in the application to the large diameter duct is slightly insufficient. Fireproof insulation for the sandwich material, the intermediate sandwich material, thickness, full of degree can not visually check, the material can not be replaced in a timely manner after the decay of moisture.

To sum up, whether it is fireproof coating or glass wool products directly as a smoke pipe fireproof material can not stand up to scrutiny; fire insulation outside the parcel material is also subject to the cost of labor, the material itself, the limitations; integration of composite air ducts are a mixed bag of good and bad, should be from the characteristics of the material, the type of inspection and other aspects of strict control. The market is in urgent need of a fireproof and heat insulation performance is stable under the premise of meeting the national standards, the site can be flexibly processed, low-cost fireproof air duct solutions.


The product is an assembled integrated composite fireproof smoke exhaust duct, the core layer of which is 400kg/m³ Ankuang fireproof duct board, the structure of the duct is Ankuang fireproof duct board plus flange, and the connectors are assembled with the integrated duct to form a solid finished duct.


 Configuration table of fireproof imitation smoke exhaust duct of Dansn


Product Solutions

Duration of fire protection



Outer color steel + inner aluminum foil scheme

Customized Ducts


Ankang Fireproof Duct Board 14400



Ankang Fireproof Duct Board 20400



Ankang Fireproof Duct Board 40400


Double-sided aluminum foil solution

Customized Ducts


Ankang Fireproof Duct Board 14400



Ankang Fireproof Duct Board 20400



Ankang Fireproof Duct Board 40400


Ankang Fireproof Duct Board

Ankang fireproof air duct board is A1 grade fireproof new material, the single board can withstand high temperature of 1200℃, which has excellent fire resistance; the density is only 0.4g/cm³, under the same volume, the weight is about 1/3 of traditional calcium silicate; the thermal conductivity is 0.13W/(m-K), the ultra-low thermal conductivity ensures good heat insulation. At the same time, Ankang fireproof duct board adopts factory prefabrication method, which is convenient for on-site installation and can be installed by two workers, greatly reducing labor cost and comprehensive cost.

Ankang Fireproof Duct Board vs. Conventional Fireproof Duct Board


Traditional fireproof duct board

Ankang Fireproof Duct Board





60% reduction in mass

thermal conductivity



35% improvement in thermal insulation

wetting rate



70% reduction in wet rise rate

Veneer Soundproofing



30% improvement in noise reduction

Ankang fireproof duct board is the lightest and thinnest integrated structure on the market, which systematically solves the problems of fireproofing and heat insulation.