An article detailing smoke duct fire prevention technology

2023-01-12

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.

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