How Long Can Ordinary Cables Withstand a Fire? Understanding the 90-Minute Lifeline of NH-VV Cables

2025-09-28 02:18:51

PVC Materials: The continuous operating temperature is only 70-90°C. When the fire temperature exceeds 150°C, PVC begins to soften and melt; when the temperature surpasses 250°C, the insulation layer decomposes rapidly, releasing toxic gases such as hydrogen chloride (HCl), while losing its insulating properties, causing the cable to short-circuit and lose power. If directly exposed to flames, ordinary PVC Cables typically maintain effective functionality for no more than 5-10 minutes before being completely burned, and may even trigger a "secondary fire"—molten plastic drips can ignite combustibles below, accelerating the spread of the fire.

PE Materials: PE has even poorer heat resistance, with a continuous operating temperature of only 60-80°C. In a fire, it begins to soften at around 120°C and melts and decomposes above 200°C. Its effective resistance time is shorter than that of PVC cables, often failing in just 3-5 minutes.

Emergency System Paralysis: If ordinary cables are connected to emergency lighting, evacuation signs, fire pumps, and smoke exhaust fans, their failure will plunge escape routes into darkness, render fire-fighting systems inoperable, leave people unable to find evacuation directions, and make it difficult for rescuers to carry out fire suppression and search-and-rescue operations.

Toxic Gas Diffusion: Materials like PVC release highly toxic gases such as hydrogen chloride and carbon monoxide when burned. Hydrogen chloride irritates the respiratory tract and causes pulmonary edema; carbon monoxide quickly binds to hemoglobin, leading to oxygen deprivation and suffocation. Over 70% of casualties in fires are related to toxic gases.

Closure of Rescue Time Windows: The 5-10 minute failure time of ordinary cables is far shorter than the golden escape time (usually recommended as 5-15 minutes) and initial rescue time in building fires. If cables fail prematurely, not only is personnel evacuation hindered, but fire departments may also be unable to use elevators, fire control systems, and other equipment due to power outages, missing the optimal fire suppression opportunity.

The "High-Temperature Resistance Magic" of Mica Tape: Mica is a natural mineral with extremely strong high-temperature resistance—its melting point exceeds 1200°C. Even in intense flames of 800-1000°C, it maintains structural stability without melting or burning. NH-VV cables are wrapped with 1-2 layers of mica tape (usually gold mica or synthetic mica) around the conductors. This mica tape acts like "fire-resistant armor," isolating high temperatures and flames during a fire, protecting the conductors from burning, and ensuring normal current transmission.

"Anti-Oxidation Design" of Conductors: Copper Conductors are prone to oxidation at high temperatures, forming an oxide layer (CuO), which increases resistance and reduces conductivity. The copper conductors of NH-VV cables have higher purity (over 99.95%), and some models have tinned or nickel-plated conductor surfaces to slow down oxidation, ensuring stable conductivity of the conductors within 90 minutes.

Flame-Retardant Modification: High-efficiency flame retardants (such as magnesium hydroxide, aluminum hydroxide, and intumescent flame retardants) are added to PVC. These flame retardants decompose and absorb heat at high temperatures, or form an intumescent carbon layer that covers the surface of the insulation layer, isolating oxygen and flames and preventing continuous combustion of the insulation. The oxygen index (LOI) of ordinary PVC is only about 24% (the higher the oxygen index, the more difficult it is to burn), while the oxygen index of the insulation layer of NH-VV cables can reach over 32%, making it a "flame-retardant material" that self-extinguishes quickly even when away from flames.

Low-Smoke Zero-Halogen Optimization: Traditional PVC releases a large amount of toxic gases and thick smoke when burned. In contrast, modified LSZH-PVC reduces halogen (chlorine, bromine) content, producing extremely low smoke density when burned (meeting GB/T 17651 standards, with a minimum light transmittance of ≥60%) and significantly reducing toxic gas emissions (hydrogen chloride emissions ≤5mg/g). This reduces harm to personnel from toxic gases in fires and ensures visibility in escape routes and rescue sites.

Enhanced Mechanical Strength: During a fire, building structures may collapse or fall. The thick sheathing and reinforcement layers can protect the internal structure of the cable from being damaged by falling objects, preventing the conductors and insulation layer from being directly exposed to flames.

Extended Fire Resistance Time: The thick sheathing slows down the penetration of flames and high temperatures into the interior. Combined with the flame-retardant effect of the insulation layer, it further extends the effective working time of the cable, ensuring no failure within 90 minutes.

Test Conditions: Cable samples are placed in a simulated fire environment, continuously burned with flames at temperatures as high as 950-1000°C, while rated voltage is applied to the cables to monitor their conductive performance.

Qualification Criteria: Within the 90-minute burning period, the cables must maintain "no breakdown or open circuit," meaning they can continuously transmit current without failure of insulation performance. Only after passing this rigorous test can a cable be recognized as a "90-minute fire-resistant cable."

Escape routes remain brightly lit, allowing people to clearly see evacuation directions and avoid danger due to getting lost;

Emergency broadcasting systems operate normally, enabling management personnel to guide evacuation via broadcasts and avoid panic and crowding;

The Emergency Power Supply for elevators (if NH-VV cables are used) remains operational, facilitating the evacuation of people with limited mobility (the elderly, disabled individuals) (Note: Elevators are generally not recommended for ordinary personnel during fires, but emergency elevators rely on fire-resistant cables for power supply).

Fire Pumps: If the Power Cables for fire pumps are NH-VV cables, the pumps can operate continuously for 90 minutes, delivering fire-fighting water to the fire area and controlling the spread of the fire;

Smoke Exhaust Fans: Smoke exhaust fans can discharge thick smoke generated by the fire to the outside, improving visibility and air quality at the rescue site. NH-VV cables ensure the continuous operation of smoke exhaust fans, creating a safe environment for firefighters to extinguish the fire;

Fire Control Rooms: Fire control rooms are the "command centers" for fire rescue. If the power supply and signal Transmission Cables of the control room are NH-VV cables, the control room can normally monitor the fire situation and operate fire-fighting equipment within 90 minutes, avoiding "command failure" due to power outages.

Data Centers: If the power supply and data transmission cables of servers are NH-VV cables, staff can complete the backup of important data within 90 minutes, avoiding permanent data loss due to the fire and reducing economic losses for enterprises;

Chemical Factories: If the Control cables of chemical equipment are NH-VV cables, operators can activate emergency shutdown procedures within 90 minutes, closing valves and cutting off hazard sources to avoid more serious accidents such as explosions and toxic substance leaks caused by equipment malfunction.

Public Buildings: Shopping malls, supermarkets, cinemas, stadiums, and exhibition halls. These locations have large numbers of people and high evacuation difficulty. Emergency lighting, evacuation signs, and fire pumps must use NH-VV cables to ensure safe evacuation of personnel during fires;

Residential Buildings: For high-rise residential buildings (≥10 floors), NH-VV cables must be used for lighting in evacuation stairwells, power supply for elevator machine rooms, and power supply for fire control rooms. For low-rise residential buildings, NH-VV cables are also recommended for fire pumps and emergency broadcasting systems.

Transportation Hubs: Airport terminals, railway station waiting halls, and subway platforms. These locations not only have dense personnel but also involve transportation scheduling systems (such as subway signal systems and airport flight scheduling systems). NH-VV cables ensure the normal operation of scheduling systems during fires, avoiding transportation paralysis;

Medical Buildings: Operating rooms, ICUs (Intensive Care Units), and emergency rooms in hospitals. The medical equipment (such as ventilators and ECG monitors), emergency lighting, and backup power supply in these areas must use NH-VV cables to ensure uninterrupted operation of medical equipment during fires and protect the lives of patients.

Chemical Enterprises: Production workshops and storage tank areas in chemical factories. These areas contain flammable and explosive substances, posing high fire risks. Equipment control cables and fire-fighting system cables must use NH-VV cables to avoid secondary explosions caused by fires;

Data Centers: Power Supply Cables and data transmission cables in server rooms. NH-VV cables are recommended to ensure data backup can be completed during fires and reduce losses for enterprises.