Comparison Between Normally Open and Normally Closed Fire Doors: Control and Compliance
According to GB50045-95 Code for Fire Protection Design of Tall Buildings, Article 5.4.2, fire doors installed in evacuation corridors, stairwells, and antechambers should possess an automatic closing function. For normally open fire doors, it is mandatory that they automatically close during a fire and provide feedback signals. This regulation was once included in the mandatory construction standards of 2000 (although omitted in the 2002 edition). Furthermore, the GB50116-98 Code for Design of Automatic Fire Alarm Systems, Article 6.3.7, specifies the requirements for the control of normally open fire doors by fire control equipment:
- 6.3.7.1: Upon detection of a fire by any fire detector on either side of the door, the fire door should automatically close.
- 6.3.7.2: The closing signal of the fire door should be transmitted to the fire control room.
Despite these clear regulations, many high-rise buildings do not adhere to them. Through years of engineering review, I have noticed that while many high-rise buildings incorporate normally open fire doors, their design drawings rarely comply with the above standards. Construction teams working on fire alarm systems often claim to have never installed fire door control systems, and many are unfamiliar with fire door release switches. Alarm equipment sales representatives echo this, noting that design drawings rarely include automatic control features for fire doors. Even in completed projects, such as luxury hotels, it is rare to find release switches installed for normally open fire doors.
According to manufacturers of fire door release switches, there is minimal demand for these components in many cities. This widespread disregard for regulations raises concerns about fire safety in smaller urban areas, where it seems that the relevant standards are often neglected.
Why Are Fire Door Standards Not Being Followed?
Is the problem due to insufficiently strict standards? Clearly not. The language in the standards indicates that compliance is mandatory. Is it because normally open fire doors are uncommon in high-rise buildings? On the contrary, they are quite prevalent, as I will explain. Is the cost too high? Again, no. A fire door release switch costs about 350 RMB per unit (with imported products being more expensive), which is only slightly more than the cost of a detector. Compared to motorized fire shutters, the expense is negligible. So, where does the problem lie, and what can be done about it?
One primary issue is the lack of clarity in architectural design drawings, which often do not specify which fire doors are normally open and which are normally closed. Electrical designers, who might not thoroughly analyze the building’s functional needs, tend to overlook normally open fire doors. Additionally, some electrical designers may not be fully familiar with the relevant codes.
Another factor is that fire alarm equipment manufacturers typically do not produce fire door release switches, and their product catalogs rarely feature examples of automatic closing mechanisms for normally open fire doors. As a result, designers are unfamiliar with the necessary methods for incorporating such systems.
Moreover, domestic manufacturers of fire door release switches have not effectively promoted their products. They often focus their marketing efforts on fire doors and door closers, leaving electrical designers unaware of the existence of these switches. This lack of awareness is a significant contributor to the problem.
Finally, some designers may have misconceptions, believing that the control system for a normally open fire door is as complex as that of a fire shutter, or that motorized fire doors require a complicated motorized system similar to automatic doors, leading them to mistakenly think that such systems are prohibitively expensive or require high-voltage power supplies. This misunderstanding can cause designers to deliberately avoid specifying these systems.
By addressing these misconceptions and ensuring that design teams are familiar with the relevant standards, we can improve compliance and ensure that fire doors function as required, providing the necessary protection in the event of a fire.
From the above two examples, it’s clear that normally open fire doors are commonly found in high-rise buildings. Some may wonder, “Why not just convert normally open fire doors into normally closed ones to avoid automatic control?” The author believes this approach is absolutely inappropriate for several reasons.
Firstly, operating fire doors manually can be inconvenient, particularly in high-traffic areas, where frequent opening and closing may reduce the lifespan of the doors and their components. Over time, this could lead to doors being propped open, compromising fire safety. In an emergency, people in panic are unlikely to remember to close these doors, leaving evacuation routes unprotected. Even if someone attempts to shut the door, it may have been wedged or damaged, rendering it ineffective in preventing the spread of fire and smoke.
When the self-closing mechanism is compromised, the door loses its resilience to withstand the pressure of hot air during a fire, allowing smoke and flames to breach critical areas such as stairwells and corridors. This not only endangers the lives of evacuees but also hampers firefighters’ access to the scene, leading to catastrophic consequences. Thus, it’s essential that normally open fire doors remain as such and are automatically controlled to ensure they close during emergencies.
Normally closed fire doors typically consist of the door leaf, frame, door closer, and seals. For double or multi-leaf doors, sequence selectors are also installed to ensure proper closure. In contrast, normally open fire doors require an additional fire door release switch, which works to automatically close the door in case of a fire.
Fire Door Release Switch Operation
The fire door release switch (example model: ZDK-905) weighs approximately 1kg with dimensions of 150x150x50mm, similar to a standard 86-series switch panel. It is typically mounted on a wall or a custom bracket at a height of around 1.5 meters, and its installation resembles that of a conventional wall switch. However, a dedicated and securely embedded junction box is required to withstand the impact of the door leaf.
The switch panel includes a recessed slot where a metal latch from the door leaf fits, holding the door in the open position. A chain or button on the switch allows for manual release in case of an emergency, relying on the door closer and sequence selector to ensure the door shuts tightly. The holding force of the metal latch can be adjusted between 10 and 50 kg.
The release switch is typically operated electromagnetically, powered by a 24V DC external control power source from the fire alarm system, with a working current of less than 0.3A. Once triggered, the switch cuts power to the electromagnetic holding device, allowing the door to close automatically. A feedback system ensures the status of the door is relayed to the fire control center.
Alternatively, some switches use temperature-sensitive components, such as memory alloys, that release the latch when the ambient temperature reaches 70°C, mimicking the operation of fire dampers. Hybrid models, like the ZDK-902, combine both electric and thermal control for enhanced functionality.
Automatic Control of Normally Open Fire Doors
In most residential buildings, normally open fire doors are typically installed as single or double-leaf swing doors. Smoke detectors installed nearby trigger the release of the door via the fire alarm system, allowing the door to close automatically during an emergency.
Firefighters can also control these doors manually from the fire control room. After the fire, the doors must be manually reset on-site, with feedback signals sent to the control room to confirm the reset.
In contrast, sliding fire doors, like those produced by Beijing New Fire Equipment Factory, are held open by magnetic forces. When a fire is detected, power is cut to the magnets, and the door closes under its own weight. This system can operate independently or be integrated with a building’s fire alarm system.
Automatic Control of Normally Closed Fire Doors with Security Functions
For fire doors with security requirements, electromagnetic locks are used to secure normally closed doors, requiring a key for entry. During a fire, these locks are automatically disengaged via the fire alarm system, allowing evacuees to push the door open for escape.
The conflict between fire safety and security is an issue that needs to be addressed in modern buildings. Fire doors, especially those with automatic controls, must strike a balance between facilitating safe evacuation and maintaining security.
Conclusion
In conclusion, fire codes impose strict requirements for the automatic control of fire doors. Electric design professionals should not overlook this aspect when designing fire safety systems. Both normally open and normally closed fire doors play a critical role in maintaining the integrity of fire compartments and ensuring safe evacuation routes. Building designers and owners should prioritize automatic fire door control to meet regulatory requirements and enhance overall safety.
With automatic control mechanisms being both cost-effective and reliable, proper implementation of fire doors is essential for effective fire safety management.
