Building and Construction

London Highrise Blaze Highlights Fire Systems and Codes

14 June 2017

At least 12 people died after a fire engulfed a 24-story-tall apartment building in London on June 13-14. Police initially expected the number of victims to rise.

Initial reports said the fire began on the fourth floor of Grenfell Tower, although the exact cause had yet to be determined. The fire reportedly spread quickly and engulfed virtually the entire building.

The BBC says that Grenfell Tower was built in 1974 by Kensington and Chelsea Borough Council. A two-year £10 million ($12.8 million) refurbishment was completed by Rydon Construction in 2016. Work reportedly included new exterior cladding, replacement windows and a communal heating system. The BBC says "extensive remodeling of the bottom four floors" was completed, creating nine additional homes, and improvements to communal facilities.

Multiple systems are typically used to detect, report, and suppress fires in commercial and residential buildings. In addition, multiple local and international building codes and standards exist and apply to virtually all new construction.

Learn more about fire detection and suppression systems, suppliers, and standards here.

Fire Alarm Control Panels

Fire alarm control panels (FACPs) relay fire detection and response communications between detectors, alarms, suppression systems, and monitoring stations.

Traditional FACPs are hardwired to each device in the system. The panel recognizes when the current or resistance on a circuit increases from the activation of a detection appliance, such as a smoke, heat, or flame detector or a manual call station. Wireless panels and accompanying devices are radio-linked.

A panel accordingly triggers visual, auditory, and occasionally other types of notification devices to alert inhabitants of an emergency situation; this most often results in the building's evacuation.

Important and invaluable structures will have a fire suppression system consisting of water sprinklers, dry or wet chemical dispersal systems, or a gas blanketing system. Simultaneously the panel informs a monitoring center of the alarm status and individuals at the receiving location determine ensuing procedures. The panel can also control HVAC systems, building automation controllers, access points, and elevators to isolate the fire or route personnel during an emergency.

Components

An FACP usually contains these components.

Interface: Provides keys so operators can input commands to the FACP, often in response to updates supplied by an integral display.

Battery: Used as a short-term power supply in the event the main power supply is interrupted.

SLC loops: Provides communication to addressable input and output alarm appliances.

Notification appliance circuits (NACs): Circuits explicitly used to initiate auditory and visual alarms.

Relays: Typically used to interface the FACP with other building systems, but can also be used to link appliances.

Phone jacks: Links the FACP to a digital communicator which will sever all phone connections not related to the FACP.

Power conditioner: Protects the FACP from electrical surges, spikes, sags, overvoltages, brownouts, and electrical noise.

Cabinet: This mounted, metal casing shields internal components but typically allows access to the display, and possibly the keypad. The cabinet is easy to visually identify and protects the FACP from tampering and mild environmental threats (dust, moisture, etc.).

Main circuit board: Consists of the FACP's microprocessor, power supply, primary components, and wiring connections.

The following fire alarm system components are typically linked to a fire alarm control panel via SLC loops, NACs, and relays: flame detectors; heat detectors; smoke detectors (ionization, photoelectric, etc.); CO detectors; fire sprinklers; radio repeaters; signal translators; node panels; and fire suppression systems. Emergency call systems are usually hardwired via phone lines.

Modern FACPs are distinguished by how fire alarm devices are wired to the panel, which also indicates how the panel identifies the location of a fire.

Addressable FACPs

FACP alarm types: This type of FACP terminal pinpoints which component or components of the fire alarm system have been activated, significantly narrowing the probable location of the fire and providing responders a better chance to extinguish the fire before it spreads.

Addressable FACPs connect all system appliances using a signaling line circuit with both ends terminating at the panel. It is more reliable than a conventional FACP due to the fact that if one side of the wire is severed, loop isolation modules ensure the device can communicate with the control panel.

Addressable FACPs are more expensive but are easier to install, and their complete versatility may prove efficient in the long run, especially for medium- to large-sized buildings.

Wireless FACPs: Wireless FACPs are short-range devices that are a common, modern, and credible alternative to hardwired FACPs.

Panel and appliances communicate at a low transmission power level in accordance with legislation. This communication can be unidirectional (transmitter→receiver) or bidirectional (transceiver).

System appliances are typically battery powered, and there is a low chance FACPs will create or receive RF interference. The most common modulation schemes and data transmission protocols are amplitude shift keying (ASK), frequency modulation (FM), and frequency shift keying (FSK). Wireless detection and alarm devices have a maximum range of 250 m, but signal repeaters, networked panels, and additional nodes extend this matrix. Several hundred devices can be uniquely identified by some wireless FACPs.

Conventional FACPs: Also known as collective FACPs, this type of control panel sections the structure into zones. Each zone has devices wired in parallel, and therefore the panel serves to identify which zone of detection equipment has been triggered; the panel only displays the alarm or fault status of the circuit, but this type of protection is usually sufficient for smaller-sized buildings.

Since each zone is individually wired to the panel, if the circuit is broken integrated devices will become unresponsive. Conventional FACPs have less capital expense than the addressable variety, but have longer and more costly installations.

Networking

Large buildings and campuses are best protected by multiple panels that have been linked within a local area network and communicate via a proprietary protocol (BACnet, Arcnet, etc.). All integrated detection systems can be addressed and monitored from a single panel or monitoring station. The redundancy prevents system downtime from failures or maintenance. Network hierarchies determine which panel has priority during an alarm.

Wireless panels are often linked via mesh networking, a system where each appliance is outfitted with a transceiver and can communicate with other local devices. This is useful in complex, large, and unpredictable environments. Hardwired panel networks must determine with which layout topography to wire panels.

A comprehensive FACP will provide these capabilities:

Selecting fire alarm panel functions Acknowledge (Ack): A user-input command to indicate the receipt of an alarm, trouble, or supervisory signal.

Circuit supervision: By applying a pulsed or time-dependent variable voltage to the circuit, the panel and operator can determine if there is a fault in the alarm circuit.

DC power: The panel has an integrated battery or capacitor to run the panel in the event AC power has been discontinued.

Disable mode: Appliances in zones or circuits of the system can be temporarily suspended from activating.

Drill: Activates alarm appliances only for the purposes of conducting a building evacuation exercise.

Flash test: Tests the status of LED indicators on the panel.

Reset: All system appliances and the panel are reverted to monitoring status.

Silence: During an alarm status, it eliminates all audible alarm devices, but may or may not shut off strobes or other visual alarms.

Supervisory: Communicates that a portion of the fire alarm system has been disabled, or that a low-priority detector has been activated.

Trouble: This indicates that a device, circuit, or power supply has been compromised.

Walk test: Alarm inputs will operate notification appliances for a predetermined increment. This allows personnel to inspect devices without having to continually trigger the alarm.

Features

Alarm type: Panel is compatible with continuous, march time, temporal, California, two-stage, slow whoop-style, or verbalized audio notifications.

Alternative operations: The panel can elicit security personnel or alert building inhabitants of localized, non-fire threats, such as a tornado or flood. Audible notifications are usually limited or disabled.

Annunciator: LEDs visually indicate the status of devices wired to the FACP, which is integral or connected to the panel.

Auto-program: This mode will automatically identify all devices on the circuit and assigns each an address, as well as determine appliance activation sequences.

Connectivity: Panel has ports or configurations for plug-in external keyboards or printers.

Display: FACP contains a touchscreen or LED backlit display.

Flash memory: Panel recalls system history.

Pre-alarm: A two-stage alarm that requires more than one device to be activated or a preconfigured amount of time to pass before initiating the notification phase.

Remote access: Panel can be programmed or interrogated from a central control station.

Second priority: Allows a secondary monitoring system, such as a security or building control system, to have an input into the FACP. This may or may not result in an alarm triggered by the FACP.

Monitoring

An essential component to most commercial, networked, or large-scale FACPs is a centralized monitoring station where the FACP reports its operational status.

This station can be an on-campus security or management office; a contracted third-party monitoring center; or, rarely, municipal emergency services. Furthermore, the panel can be operated from this remote location.

This operational redundancy ensures that the alarm panel can be addressed even if inaccessible due to smoke or flames, and that appropriate individuals are notified. Older-style FACPs and those located in rural settings typically link to control centers via POTS (plain old telephone service). More recent FACPs link via web access, cellular networks, or RF transmission.

Standards

Local and regional governments often adopt codes that have been outlined by trade and standards organizations as official policy, such as the International Building Code or National Building Code of Canada.

Fire alarms and associated instruments are typically regulated by a specialized body or panel, and the aforementioned codes utilize National Fire Protection Association 72. Underwriters Laboratories evaluates fire alarm products and records conclusions in an effort to provide code-making bodies with the most relevant and up-to-date data regarding life safety code.

As a result, there are several important documents to reference when considering fire alarm control panels, and they have been listed according to priority.

International Building Code: Dominant building code in the United States

National Building Code of Canada: Construction regulations in Canada

Approved Document B: Fire safety regulations for buildings in England, Wales

NFPA 72: Regards all aspects of fire alarm performance (composed for North America)

ISO 7240: Fire safety standards developed by ISO (used in Australia, China, Russia)

Fire Suppression Systems

Fire suppression systems are used to suppress flames in the event of a fire. There are several types of suppression systems including:

  • Wet sprinkler systems
  • Dry sprinkler systems
  • Deluge sprinkler systems
  • Dry chemical suppression systems

These systems work in conjunction with heat sensors, smoke detectors, and fire alarm systems to improve and increase public safety. They are used to protect art treasures, architectural landmarks, oil tankers, data centers, factories, offices libraries, vehicles, and restaurants.

The working principle of fire suppression systems differ for various types, though generally these systems employ a combination of the removal of oxygen and the lowering of the ignition temperature. Removal of fuel from an active area is seldom practical or even feasible.

The most common method of fire suppression is the lowering of the ignition temperature with large quantities of water. Normal atmospheric oxygen content is approximately 21%. If the percentage falls below 15%, the quantity of oxygen available will no longer support combustion.

Different types of fire suppression systems include:

  • Dry fire suppression systems that extinguish fire by interrupting chemical reaction at the fire triangle
  • Carbon dioxide systems that extinguish fire by removing oxygen and heat with a cold discharge
  • Clean agent fire suppression systems that utilize halogenated extinguishers to suppress the fire by interrupting the chemical reaction at the fire triangle
  • Inert fire suppression systems that utilize inert gases as agents, which are non-toxic, non- corrosive, and odorless
  • Restaurant fire suppression systems that mainly utilize portable liquid agent systems
  • Vehicle fire suppression systems where mobile equipment serves all types of vehicles
  • Water atomizing fire suppressing systems where a pair can produce 1.5 trillion water droplets per second equivalent to cover a soccer field in a minute
  • Wet chemical fire suppression systems that prevent fire by creating a barrier between fuel and oxygen
  • Water and foam fire suppression systems that extinguish fire by taking away the heat and separating oxygen from other elements

Fire suppression systems serve as life and property protection. Users should be well trained to use the equipment. Operating these systems without proper training can cause damage to the equipment, property, and people.

To contact the author of this article, email david.wagman@ieeeglobalspec.com


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Discussion – 2 comments

By posting a comment you confirm that you have read and accept our Posting Rules and Terms of Use.
Re: London Highrise Blaze Highlights Fire Systems and Codes
#1
2017-Jun-15 9:09 AM

The article has a lot of information about various types of fire detection systems and components, but says nothing about how all this information may have related to the London fire. Nor does it say anything about the specific codes in effect regarding London England (the ones cited were for other locations, primarily in North America). In a publication such as CR4, with its international audience, I would have expected better.

--JMM

Re: London Highrise Blaze Highlights Fire Systems and Codes
#2
In reply to #1
2017-Jul-14 8:14 AM

I fully agree, whats the point of this article and it's relation to the London Highrise fire.

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