Fire alarm system

A fire alarm system is a specialized building network designed for safety. Its primary purpose is to detect the presence of fire, smoke, or carbon monoxide. Once a threat is found, the system must alert the people inside the building. It also alerts emergency forces so they can respond quickly. Most commercial buildings are required by law to have these systems installed.

The system operates through a precise sequence of communication. It begins with initiating devices, which act as the system's inputs. These devices can be activated automatically by sensors or manually by people. Once an input is triggered, the signal travels to the Fire Alarm Control Panel (FACP). The FACP is the central hub of the entire network. It monitors the integrity of the system and manages all outputs.

There are two main types of initiating devices. Manually actuated devices are often called pull stations or call points. These are placed near exits so people can operate them by pulling a lever or breaking glass.

Automatically actuated devices respond to physical changes in the environment. Heat detectors sense thermal energy, while smoke detectors find products of combustion. Some advanced systems use cameras and computer algorithms to analyze fire and movement. Even water-flow detectors can trigger an alarm if they sense a sprinkler has activated.

Once the control panel receives a signal, it activates notification appliances. These devices use various stimuli to ensure occupants take action. Common methods include strobe lights, horns, sirens, and bells. Some systems use speaker strobes that combine sound with voice evacuation messages.

These messages can be pre-recorded or live broadcasts from trained personnel. In the United States, the standard audible signal is known as Temporal Code 3. This consists of a repeated three-pulse cycle with specific on and off timings.

Reliability is critical, so these systems include multiple power sources. The primary power usually comes from a 120 or 240-volt alternating current utility source. This is delivered through a dedicated branch circuit for the system. To prevent failure during a power outage, systems include secondary power supplies. These are often sealed lead-acid storage batteries or emergency generators.

These backup sources ensure the alarm works even if the building loses electricity.

Designing these systems requires following strict international and national standards. Engineers must reference specific building codes and insurance requirements. For example, ISO 7240-14 is an international standard for design and service published in August 2013. In the United States, installers follow NFPA 72, also known as the National Fire Alarm Code. Canada uses the Underwriters' Laboratories of Canada (ULC) standards. Many European countries have their own specific rules, such as VdS 2095 in Germany or BS 5839 in the United Kingdom.

In large or complex buildings, specialized communication tools are used. Emergency Voice Alarm Communication systems, or EVAC, are common in high-rise buildings and hospitals. These systems use high-reliability speakers to provide clear instructions. This is vital in "defend-in-place" occupancies where total evacuation is difficult.

In these cases, the system can play different messages on different floors. For instance, a floor with an active fire might be told to evacuate immediately. Meanwhile, floors far from the fire might be told to stand by.

Finally, fire alarm systems can interact with the building itself through safety interfaces. These interfaces allow the system to control the built environment during an emergency. They can influence air movement to control the spread of smoke. They can also manage lighting or human transport systems. Some systems even disable elevators because they can be unsafe to use during a fire. This integration helps prepare the entire building for an emergency response.