Refer below shared Fire and Gas System Interview Questions for your interview preparation.
Typically, a fire alarm system is made up of the following components:
A typical fire alarm system has numerous initiating devices divided among separate zones – each connected via an initiating device circuit to a central control panel.
The control panel performs supervisory functions over the initiating devices, indicating appliances, all associated field wiring, telephone ties, and its own internal wiring and circuit cards.
The Fire Alarm Control Panel (FACP). The FACP should be located where it can be responded to as necessary either around the clock or during operating hours.
This can be at building security headquarters, adjacent to a telephone switchboard or in a maintenance office – whichever location offers maximum coverage.
It should also be positioned in a fairly central location because if the system goes into alarm, a person needs to be able to race to the location and verify fire status before the alarm is silenced.
Also Read : Fire/Smoke/Flame/Heat/Gas Detectors
A fire alarm system operates in one of three (or more) states: normal, alarm, and trouble. The state is reported at all times on the alphanumeric display.
If the system goes into alarm, the indicating appliances throughout the building go off. These could be very loud horns for some occupancies, or softer chimes in others, such as a nursing home.
The control panel monitors the initiating device circuits at all times for shorts and open wiring by means of the applied DC voltage. The initiating devices are normally open.
In the event of a fire they become conductive at close to zero ohms. How, then, is it possible for the control panel to differentiate between a non-alarm state and an open wiring fault? This is accomplished by means of an end-of-line resistor.
The control panel also monitors the functionality of its own wiring and zone cards, and trouble is reported in the display.
Another capability of the fire alarm system is to call out in case of alarm. Two dedicated phone lines are connected, and the system performs test calls periodically in accordance with programmed instructions. If either phone line won’t connect, the system goes into the trouble state, so repairs can be made.
The essence of a fire alarm system, as opposed to individual smoke detectors, even if they are wired to indicate in concert, is that it is supervised from a central location. The whole notion of supervision is critical.
It does not mean that a person sits at the console and watches it at all times. What it means is that a supervisory voltage is applied to all circuitry, and current flow is monitored electronically to verify that equipment and wiring are intact.
If the system goes into alarm and won’t silence due to touchpad malfunction, for example, it can be disarmed after the zone is checked for fire by cutting off the power.
First, unhook one side of the battery array, then unhook the black-white-green incoming power connector. If a fire alarm system is disabled, maintenance and security personnel should initiate fire patrols throughout the building.
The telephone monitoring agency should be informed, and the insurance company contacted to verify that coverage is not voided.
Traditional fire alarm panels installed prior to 1998 were conventional zone panels.
In a zoned system, fire alarm devices in a common area or floor of a facility are connected to the same alarm initiating circuit.
Each zone requires its own circuit conductor.
This arrangement allows alarm annunciation to be reported by areas of the building to identify which device is in alarm.
Conventional panels are often used in small facilities where a few zones can provide sufficient alarm annunciation.
With the advent of microprocessors and digital electronics, addressable fire alarm control panels and devices have become more common than conventional systems for medium and large-sized facilities.
They have become more cost effective in some small applications as well.
Addressable fire alarm systems use digital encoding and multiplex technology to more accurately identify alarm locations and device conditions.
Each fire alarm device in a system is programmed with a unique address.
The fire alarm control panel is capable of communicating with a single address or a group of addresses depending on the functions required.
The communication is often multiplexed over a common cable, sometimes referred to as the signaling line circuit (SLC).
This arrangement significantly reduces the amount of cabling necessary to install the system. The communication channel allows two-way communication, thus enabling the fire alarm control panel to control as well as monitor fire alarm devices.
A significant component of addressable fire alarm system is the software programming necessary to make the system function correctly.
The programming allows for flexible applications where you want to have specific control over the inputs and outputs.
The communication technologies employed in addressable systems allow for advanced features to accommodate sensitivity changes due to age and accumulation of dust prior to maintenance.
These features are not available with the standard conventional system.
The ionization smoke detector is widely used. Its capability to detect smoke originating from fire is best utilized for clean-burning fires that produce small particles during combustion.
The ionization smoke detector consists of an alpha particle producing a radioactive source, a smoke chamber, and charged detector plates.
Also Read : Point IR Vs Open Path IR Detectors
A photoelectric smoke detector is the most common smoke detector used today. It detects smoke by using either the principle of light obscuration or light scattering.
Its capability to detect smoke originating from fire is best utilized for fires that produce large particles during combustion.
Spot type photoelectric smoke detectors using the light obscuration principle have a light emitting device, usually a light-emitting diode (LED), a smoke chamber, and a photosensitive device that receives the light directly from the light source and produces a monitored current.
Smoke that enters the smoke chamber reduces the intensity of tech light reaching the photosensitive device, which reduces the monitored current.
When the intensity drops below a certain level, the sensor control circuitry detects a drop in the current produced by the photosensitive device. When the current falls below a preset threshold, the smoke alarm is triggered.
Spot type photoelectric smoke detectors that use the light scattering principle are constructed similarly to the detectors that use the light obscuration principle except that the photosensitive device is set so that it cannot see the light source directly.
When smoke enters the chamber, the smoke particles reflect the light from the source into the photosensitive receiver. When sufficient light intensity is detected, the alarm is triggered.
Beam detectors are line-type photoelectric detectors consisting of a separate light source and photosensitive receiver.
These devices are usually installed in large open areas where there is an unobstructed line of sight between the light source and the receiver and where the use of spot-type detectors would be economically unfeasible due to the number of detectors required.
For environments where detection of smoke is most critical, an air-sampling system provides the earliest possible detection.
An air sampling or aspirating type fire detection system is a self-contained smoke detection package compromised of five primary components:
It uses a network of pipes to continuously draw air samples and direct them to a central smoke detector.
The system operates with a network of sampling pipes that extend into the protected area. The pipes are usually made of a thermoplastic material.
An internal aspirator continuously draws air into the piping network. The systems use either a filter assembly or laser particle counting technology to filter out airborne dust and debris particles, which helps to eliminate false readings.
Typical locations or hazards for Air-Sampling smoke detectors:
Fixed Temperature Thermal Detectors can respond to:
Typical fixed temperature spot-type smoke detectors contain a bimetallic switch element that closes at a specified temperature limit. The switch is normally composed of two metals, each having a different temperature coefficient of expansion.
As this bimetallic element heats the metal with higher coefficient of expansion, it causes the switch to bend or curve, closing the switch; thus indicating an alarm condition.
Line type thermal detectors are cables that detect heat along their entire length. A line type thermal detector may consist of two wires that are separated by an insulator.
After the heat builds to a certain level the insulation melts, allowing the wires to touch and current to flow, initiating an alarm.
Bimetallic spot and coaxial style thermal detectors are self restoring. Fusible link and melting insulation types of line thermal detectors are not self-restoring.
Rate-of-Rise Thermal Detectors measure the rate at which the air temperature changes during a fire event. Measuring the change in temperature provides a faster alarm response than measuring the temperature level in a space.
The rate-of-rise detector measures the change in the temperature of the space through the use of a differential pressure switch. This switch contains an air chamber separated for the air in the ambient space by a flexible diaphragm.
As air in the ambient space changes temperature, the air pressure increases, creating a differential pressure across the diaphragm.
The air chamber is constructed with a calibrated leak so that normal temperature and pressure fluctuations within the room space adjust across both sides of the diaphragm and will not cause the alarm contacts to close.
During a fire, the air temperature rises at a rate faster than normal, causing an increase on the room side of the diaphragm diaphragm. The leak cannot compensate, and therefore the diaphragm moves and closes the detector contacts.
Combination rate-of-rise and fixed temperature thermal detectors are also manufactured and have both technologies built in.
Rate-compensated thermal detectors are devices that are designed to activate at a predetermined temperature in a space regardless of the rate at which the temperature in the space increases.
This is accomplished by compensating for the thermal lag between the room temperature and the interior of the device.
Construction consists of an outer metal tube that expands at a fixed rate. Within this tube, alarm contacts close when a certain expansion distance is reached, but this expansion is opposed by another metal device.
At a slow rate-of-rise in temperature, the outer tube expands drawing the contacts closer together.
The inner metal device exerts a counter force, keeping the contacts separated until the entire device has been heated to its rated temperature.
At a rapid rate-of-rise in temperature, the outer tube expands faster than the inner device can compensate.
Therefore, the alarm contacts close when the entire device has been heated to a lower level, thus compensating for thermal lag.
Flame detectors are used to detect the light radiation component of a fire.
Typical detectors of this type detect the wavelength of either IR or UV or a combination of the two.
These detectors are extremely fast acting and are used in areas where rapidly occurring fires or explosions could occur.
Also Read : Probability for a Safety System
These detectors respond to the various gases produced during the combustion process.
The Fire-Gas detector employs two types of technology to predict the fire. One method uses a semiconductor material that changes the metals conducting potential in a fire situation.
The other method uses a catalytic element encased in an aluminum bead.
Carbon monoxide is a colorless, odorless gas that is produced by certain gas-powered appliances and engines.
If a gas leak occurs, carbon monoxide can build up in certain areas. If a person is exposed to the gas for an extended period of time, he or she can suffer serious complications.
For this reason, many residences and commercial buildings have carbon monoxide detectors, similar to smoke detectors, installed to prevent injury to occupants.
Fire safety inspectors check safety equipment and alarms to ensure that they are in compliance with codes and regulations and will keep people and property safe in the event of a fire or other accident.
Sometimes, firefighters are called to buildings because of a malfunction in the automatic fire alarm system or because the system is triggered by something other than a fire.
Since a false alarm, also known as a preventable response, causes such a drain on resources, city fire departments may fine the owners of buildings for these preventable false alarms.
These fees are meant to encourage building owners to keep their systems in top working order through regular inspections by a certified inspection service.
They also help fire departments increase their resources for responses to actual emergencies.
With regular service and maintenance, you can prevent false alarms with your fire prevention systems.
A flow test is a procedure performed by fire safety inspectors to ensure that fire sprinkler systems are working properly.
This test is required in order to make sure that a fire sprinkler system will be able to supply enough water during a fire.
Even if primary water supply systems fail during a fire, fire sprinkler systems should still be able to deliver enough water to contain a fire.
The NFPA is the National Fire Protection Association, a fire prevention and safety organization.
The NFPA creates and publishes fire safety codes and standards to reduce the risk of fire.
The NFPA has standards for each building’s sprinkler systems and alarm systems.
Fire safety inspectors will check sprinkler heads, pipes, flow water, pressure, valves, smoke detectors, pull stations, and batteries so that they comply with these codes and standards.
Without these standards and codes, buildings would be at a high risk of fire danger.
Whether you live in a high rise apartment or work in an industrial setting, it is important to understand how to operate a fire extinguisher.
Most occupational settings with high fire risks should go through safety training to show employees how to properly use a fire extinguisher.
Even if you have had no proper training, you can learn the “PASS” method:
There exist several different types of fire extinguishers, each designed to fight particular types of fires.
They are organized into different classes of fires, including:
Water cannot put out all fires – in fact, it can make some fires even worse. Your workplace should have the proper type of fire extinguisher installed to help fight the type of fire most likely to occur.
Depending on the agent that fuels the fire, fires are classified into different categories:
Different fire extinguishers are specially designed to fight different classes of fires. Fire safety is absolutely essential for protecting both human life and property investments.
Each sprinkler head is held closed by a small piece of heat-sensitive material. This piece acts as a plug to prevent water from flowing at normal temperatures.
When heated by a fire, the sprinkler heads near the fire are activated and release water to put out the fire.
To keep the pressure steady and avoid overwhelming local water suppliers, the entire system is powered by a fire pump, which pumps water at large volumes from a separate water source.
A fire pump is an integral part of fire sprinkler protection systems in large buildings. Local water systems do not have the capacity to provide a steady stream of water throughout a fire sprinkler system in the event of a fire.
The fire pump is connected to a separate source of water and has the power to pump large volumes of water, even to the top floor of a very tall building, in a continuous flow.
Fire pumps require regular inspection and maintenance in order to ensure that the entire sprinkler system will function properly in the event of a fire.
Different types of fire sprinkler systems have been designed to meet the optimum needs of your commercial building, no matter what your business or industry.
Types of fire sprinkler systems include
Each type of system has its own set of advantages and disadvantages.
If a person intentionally sets a fire to a structure, they can be charged with the crime of arson.
Businesses and restaurants, as well as residential buildings, are all at risk for arson.
A clean agent is a fire-suppressing chemical in a gaseous form that will not harm electrical equipment or other objects that are easily damaged by water.
Clean agents are also easier to clean up than other types of fire suppression systems.
A clean agent fire suppression system is a good option for use in areas that can be harmed by water or other types of fire suppression chemicals.
Active fire protection is a method which uses automatic or manual systems to detect and suppress fires.
Active fire protection includes fire suppression efforts with fire extinguishers, sprinkler systems, and fire detection equipment such as smoke alarms.
Any active fire suppression system must be properly installed and maintained to comply with local building and fire codes.
HazMat is an abbreviation of “hazardous materials.”
A HazMat Operations certificate shows that we have had the special training necessary to recognize hazardous materials and dangerous goods.
It is necessary for those working with water lines and fire prevention systems to have a complete understanding of hazardous materials and how to protect nearby people, property, and the environment from the effects of exposure.
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