1.What are the basic fire protection characteristics of galvanized cable trays?
High temperature resistance of steel: Steel is a non-combustible material (combustion performance grade is A grade) and has stable mechanical properties at room temperature. When the ambient temperature rises, the strength of steel will change with the temperature rise:
When the temperature is ≤300℃, the strength of steel remains basically stable;
When the temperature reaches 400-500℃, the strength drops significantly (about 60%-70% of the strength at room temperature);
When the temperature exceeds 600℃, the strength is almost lost, and the steel will deform and collapse due to softening.
This feature makes the galvanized bridge itself non-combustible and non-flammable gas, and can provide structural support for the cable at the beginning of the fire.
High temperature performance of the galvanized layer: The melting point of zinc is about 419℃ and the boiling point is about 907℃. When the ambient temperature exceeds 419℃, the zinc layer will gradually melt and drip. At this time, the anti-corrosion effect of the galvanized layer will fail, but it will not aggravate the fire (zinc itself is non-combustible, and the melting process does not produce combustion-supporting substances).
2.What are the fire protection limitations of galvanized cable trays?
Insufficient structural stability at high temperatures:
When pure galvanized bridges are not treated with fireproof reinforcement, they can only rely on the steel's own high temperature resistance to maintain their structure during a fire. When the fire temperature exceeds 500℃ and lasts for a long time, the bridge may deform and collapse due to the softening of the steel, and it may no longer be able to support the cables, or even compress the cables to aggravate the spread of the fire (such as the cable insulation layer falling off after burning).
No heat insulation ability, accelerated cable heating:
The metal material of the galvanized bridge has strong thermal conductivity. The high temperature in a fire will be quickly transferred to the internal cables through the bridge, causing the cable insulation layer (such as polyvinyl chloride, cross-linked polyethylene) to reach the ignition point (usually 200-300℃) in a short time, accelerating cable combustion and short circuit.
3.What are the key measures to improve the fire resistance of galvanized cable trays?
Apply fire retardant coating
Principle: Apply fire retardant coating (such as intumescent fire retardant coating) on the surface of galvanized bridge. In case of fire, the coating will expand due to heat to form a honeycomb insulation layer, which will block heat transfer and slow down the heating rate of steel.
Effect: According to the coating thickness and fire resistance level, the bridge can maintain structural stability within the specified time, which can provide time for cable evacuation or power outage.
Fireproof sealing and separation
Internal sealing of the cable tray: Use fireproof bags, fireproof mud and other materials to seal the gaps where the cable tray passes through the floor slab, firewall and other parts to prevent the spread of flames and smoke.
Choose fire-resistant galvanized bridge frame
Special process: Some manufacturers produce "fire-resistant galvanized bridge frame" by thickening the steel thickness and composite insulation layer, and its fire resistance can reach a specific level after testing.
4.What are the fire performance requirements in different scenarios?
Civil buildings: According to the "Architectural Design Fire Protection Code", bridges that pass through fire partitions must be fireproof and blocked, and the fire resistance limit is consistent with the wall where they are located (for example, the fire resistance limit of the fire wall is not less than 3 hours).
Industrial plant: In flammable and explosive places such as chemical and metallurgical industries, bridges must reach a higher fire resistance level and cooperate with explosion-proof design.
Underground projects: In underground garages, tunnels and other scenes, bridges must have the ability to resist smoke and heat radiation, and usually require a combination of fire retardant coatings and blocking measures.
5.In summary, what is the fire resistance performance of galvanized cable tray?
The basic fireproof performance of galvanized cable trays comes from the non-combustibility of steel, but its metal thermal conductivity and strength attenuation at high temperatures are natural shortcomings. In practical applications, measures such as applying fire-retardant coatings, fire-proof blocking, and fire-resistant design are required, combined with the fireproof characteristics of the cable itself, to meet the fire protection requirements of different scenarios. When selecting, it is necessary to balance cost and performance based on the fire protection level standards of the specific project to ensure that the cable safety can be protected in a fire, and the spread of the fire can be delayed, buying time for personnel evacuation and fire fighting and rescue.