The key role of magnesium hydroxide flame-retardant cable in high-rise building fire protection system
With the acceleration of urbanization, the number of high-rise buildings has increased dramatically, and fire safety issues have become the focus of social attention. In the fire protection system of high-rise buildings, the fire resistance of cables is directly related to the emergency response capability and personnel evacuation safety when a fire occurs. In recent years, magnesium hydroxide flame-retardant cables have gradually become the "invisible guard" of high-rise building fire protection systems due to their unique fire protection characteristics. This article will deeply explore the technical advantages, application scenarios and great significance of magnesium hydroxide flame-retardant cables to the fire safety of high-rise buildings.
1. Special challenges of high-rise building fire protection systems
High-rise buildings (usually buildings with a height of more than 24 meters) have significantly higher fire risks than ordinary buildings due to their high floors, dense population and complex evacuation passages. According to statistics, about 35% of the fires caused by electrical lines worldwide each year occur in high-rise buildings. Such fires are often caused by cable short circuits, overloads or external fire sources. The fire spreads quickly and is difficult to extinguish, which can easily cause major casualties and property losses.
The core requirements of the fire protection system for cables:
1. Flame retardant performance: no combustion or delayed combustion under high temperature or open flame;
2. Low smoke and non-toxicity: the smoke and gas released during combustion must meet safety standards;
3. High temperature resistance: maintain circuit integrity for a certain period of time in a fire to ensure the normal operation of emergency equipment (such as smoke exhaust systems, fire elevators).
2. Technical principle of magnesium hydroxide flame retardant cable
Magnesium hydroxide (Mg(OH)₂) is an inorganic flame retardant, and its flame retardant mechanism is based on the following three aspects:
1. Endothermic decomposition: At high temperature (about 340℃), magnesium hydroxide decomposes into magnesium oxide and water vapor, absorbing a large amount of heat and reducing the surface temperature of the material;
2. Dilute oxygen: The released water vapor can dilute the surrounding oxygen concentration and inhibit the combustion reaction;
3. Form a protective layer: The generated magnesium oxide covers the surface of the cable to isolate the combustible from the fire source.
Compared with traditional halogen flame retardants, magnesium hydroxide has significant environmental advantages:
- Non-toxic and harmless: the decomposition products are water and magnesium oxide, and no toxic gases such as hydrogen chloride and dioxins are released;
- High filling capacity: the addition amount can reach 40%-60%, and the flame retardant efficiency is high;
- Strong temperature resistance: the decomposition temperature is highly matched with the combustion temperature of the cable material (300℃-500℃).
3. Application scenarios of magnesium hydroxide flame-retardant cables in fire protection systems
In high-rise buildings, the cables of the fire protection system need to run through multiple functional areas, including emergency lighting, smoke exhaust fans, fire pumps, alarm systems, etc. Magnesium hydroxide flame-retardant cables, with their characteristics, are particularly outstanding in the following scenarios:
1. Fire power supply lines
When a fire occurs, ordinary cables may fail within minutes, causing emergency equipment to be paralyzed. Magnesium hydroxide cables can maintain circuit integrity for more than 90 minutes at a high temperature of 800℃, buying valuable time for personnel evacuation and fire rescue. For example, after a super high-rise complex in Shanghai adopted this type of cable during renovation, the fire resistance time of the fire power supply system increased from 30 minutes to 105 minutes.
2. Smoke detection and alarm system
The low smoke characteristics of magnesium hydroxide cable can ensure that the smoke detector accurately detects the fire in the early stage of the fire, avoiding false alarms caused by the release of smoke from the burning of the cable itself. The measured data shows that its smoke density level (SDR) is less than 15, which is far lower than the national standard requirement of ≤60.
3. Shafts and cable trays
The cable shaft of a high-rise building is the main channel for the vertical spread of fire. The flame retardant layer of magnesium hydroxide cable can effectively prevent the flame from spreading along the line. In a tower project in Dubai, an international hotel group successfully reduced the speed of fire spread by 70% by laying such cables in the shaft.
IV. Four core advantages of magnesium hydroxide cable
1. Higher safety level
Certified by GB/T 19666 (China) and IEC 60332 (International) dual flame retardant standards, some models can reach Class A flame retardant (non-combustible materials).
2. Environmental compliance
Complies with the EU RoHS Directive and REACH regulations, and is suitable for commercial buildings with strict environmental requirements.
3. Long life and stability
The magnesium oxide protective layer can slow down the aging of the cable, and its service life is extended by 8-10 years compared with ordinary flame-retardant cables.
4. Significant economic benefits
Although the initial cost is 20%-30% higher than that of PVC cables, it reduces the hidden costs such as maintenance and compensation caused by fire risks. Calculations of an office building project in Beijing show that after using magnesium hydroxide cables, the life cycle cost is reduced by 18%.
V. Selection and installation recommendations
To ensure the maximum performance of magnesium hydroxide flame-retardant cables, the following points should be noted:
- Matching fire rating: Select the corresponding fire resistance time according to the building height (for example, it is recommended to use a fire-resistant model of 120 minutes for buildings over 100 meters);
- Reasonable wiring: Avoid cross-laying with high-temperature pipes to prevent long-term heat radiation from affecting the flame-retardant layer;
- Joint protection: Use fire-resistant sealant to perform secondary sealing on the joints;
- Regular inspection: Use infrared thermal imagers to detect abnormal cable temperature points every two years.
VI. Industry Trends and Future Outlook
With the mandatory implementation of GB 51348-2019 "Electrical Design Standard for Civil Buildings", China's flame retardant requirements for high-rise building cables have been raised to a new level. It is expected that by 2025, the market share of magnesium hydroxide flame retardant cables in the domestic fire protection field will exceed 60%. At the same time, innovative directions such as nano-magnesium hydroxide modification technology and intelligent temperature-sensitive flame retardant coatings will further promote the application of this material in super high-rise buildings.