In the USA, fires cause around $10 billion in property damage each year, while injuring or killing thousands of people. When a fire breaks out in a building, it can threaten occupants both directly and indirectly; occupants can be harmed even if they are not exposed to the heat:
Fire can weaken building elements, causing them to collapse.
Exposure to large amounts of smoke can be lethal: it contains carbon monoxide, a gas that is very toxic for humans.
If there is fire inside a building, it must be detected and extinguished as soon as possible. Therefore, having a fully-functional fire alarm system is of the highest importance. These installations can be enhanced with wireless capabilities, as long as they meet a series of key requirements. In New York City, requirements for all fire alarm systems are set forth by the following standards:
New York City Building Code, Chapter 9 – Fire Protection Systems
New York City Fire Code
New York City Electrical Code
NFPA 72: National Fire Alarm and Signaling Code, as modified by Appendix Q of the NYC Building Code.
1 RCNY §3616-04, which introduces further amendments to NFPA 72.
Low-Power Wide-Area Networks (LPWAN) are a very promising technology to deploy with fire alarm systems. The technology is not as fast as Wi-Fi, but can go across structural elements with much less attenuation; in urban settings, the range of LPWAN can exceed one mile, while Wi-Fi is weakened considerably with just a few walls.
Obtaining Fire Department Approval for a Wireless Fire Alarm System
All fire alarm systems in New York City are required to have a supervising station that is approved by the fire commissioner and compliant with NFPA 72. The initial testing procedure is carried out according to NFPA 72, and periodic maintenance and tests should be carried out according to the NYC Fire Code.
NFPA 72 Specific Requirements for Wireless Fire Alarms
The testing procedure for fire alarm systems that deploy low-power radio for wireless communication is the following:
Basic Documentation: NFPA 13 requires the delivery of as-built drawings and the manufacturer’s published instructions.
The system is set in the normal operating condition according to the instructions, and then tested for both alarm conditions and trouble conditions.
Batteries require a monthly inspection. However, if the control unit of the wireless fire alarm system monitors them automatically each day, the monthly inspection is not required.
Other than the initial testing procedure, NFPA 72 requires that the forward and reflected radio power of all wireless signals be tested once per year.
In addition to the testing procedure above, NFPA 72 provides a list of special requirements for all low-power radio systems, which is summarized in the following table:
Any low-power radio equipment used with fire alarm systems must be listed as suitable for that purpose.
A dry cell can be used as the only power supply of radio transmitters, but it must meet the requirements established in NFPA 13.16.2.
In general, the battery should be able to power the device for at least one year, and automatic notifications must be generated when it is about to be depleted (7 days in advance) or if it experiences any type of failure.
Alarm signals must be transmitted automatically and repeated at intervals of 60 seconds or less.
These signals must take priority over all others, and the control unit must display alarm activation in 10 seconds or less. When an alarm is triggered, it is required to latch in the ON position until it is reset manually.
Radio transmitters should be specifically listed as having a transmission method that is resistant to misinterpretation and interference.
The system must identify system faults appropriately, without causing a false fire alarm. For example, interference must generate a trouble signal, and removal of a transmitter must be indicated as such by the control system (NFPA article 23.16.4).
If remote appliances are used, they are also subject to requirements in terms of power supply , response time, latching and signal integrity (NFPA 23.16.5)
Wireless Network Requirements in NFPA13
When wireless communications are deployed in fire alarm systems, they must meet all applicable standards from the Federal Communications Commission (FCC) and the National Telecommunications and Information Administration (NTIA). In addition, the following requirements apply:
Unlicensed radio frequencies are not allowed.
The same radio frequency may carry fire alarm signals, integrity monitoring signals and other emergency alarm signals, but it must be used exclusively for those purposes.
NFPA 13 also establishes limits on the number of alarm boxes that can use the same radio frequency:
Networks with one-way transmission from the alarm box to the supervising station can have up to 500 alarm boxes using the same radio frequency.
Networks with two-way communication can use up to 250 alarm boxes on a single radio frequency.
If a network uses two-way communication, but the radio frequency is different for receiving and transmitting information, up to 500 alarm boxes can be used, just like in networks that use one-way communications.
In the case of public emergency alarm signals, a dedicated frequency must be designated for two purposes: reporting alarm signals and system integrity signals.
LoRaWAN Networks: A Promising Communication Tool for Fire Alarm Systems
LoRa stands for Long Range, and it is a wireless networking technology with three key characteristics:
Low energy consumption
Longer range than Wi-Fi: around one mile in crowded urban settings, around 10 miles in rural locations. When LoRa transmitters have been hanged from balloons, ranges in the hundreds of miles have been achieved.
Lower data rate than Wi-Fi: LoRa sacrifices data transmission speed to achieve increased range.
LoRaWAN is the networking standard that deals with LoRa appliances, and its characteristics make it well suited for the use with wireless fire alarm systems:
Data transmission needs are relatively low. For example, wireless fire alarm systems do not stream high-definition video signals.
Standards requires wireless fire alarm boxes to have a long battery life, and the low power consumption of LoRa devices helps optimize energy consumption. LoRa fire sensors can offer a battery life of up to 20 years!
The long range of LoRa devices allows their signal to cross floors, walls and other building elements with much less attenuation that Wi-Fi devices.
When a LoRaWAN network is deployed, signals from individual sensors are gathered in a gateway and sent to a network server for processing. The network server can then relay key information to the NYC Fire Department.
The use of wireless communications with fire alarm systems greatly reduces the upfront cost, potentially eliminating thousands of feet of wiring. In addition, wireless fire alarm systems are less susceptible to the fire itself – wired installations are taken offline if the fire melts a key power circuit or communication line.
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