Fire Alarm System Interview Questions

Fire Alarm System Interview Questions

What is the difference between a real and false alarm?

None. All alarms are real and are caused by a break in the electrical current passing through the alarm system. Alarms can be sounded by someone activating a pull station, by something as simple as toast burning near a smoke detector, or by an actual fire.

If an alarm sounds, something caused it. It might not be a fire, but don’t bet your life on it. All alarms should be treated as though they were caused by fire until it can be determined otherwise by a competent authority, such as the responding Fire Department. Over the years we have developed a dangerous complacency in response to fire alarms due to the overuse of the term “false alarm” to characterize an alarm not caused by actual fire.

What should you do if I hear a fire alarm?

Evacuate your building immediately and go to the area your supervisor has designated as a meeting point. For safety reasons, you should evacuate if you hear any alarm, even if it is not in your zone.

Why do we need NFPA 72 compliance?

NFPA 72 is a prescriptive standard that applies to Fire Alarm Systems. While the NFPA 72 standard makes no mention of gas detection, many clients are applying NFPA 72 standards and requirements to both fire and gas detection systems. There are several advantages to NFPA 72 certified systems that include:

  • Allows for the combining of both fire alarm and gas detection functions into a single safety system
  • Ensures that local “authorities having jurisdiction” like fire marshals or fire authorities have assurance that the system complies with the applicable codes and standards
  • Allows the end-user to lower their insurance costs because they are using a certified system
  • A NFPA 72 certified solution ensures that you are complying with the best practices in the industry as drafted by the NFPA

When should we use a PLC vs. a Controller-based solution for F&G ?

The choice between a PLC and Controller-based system is primarily driven by the size of the application.

PLCs are best suited for medium to large size gas detection systems (25+ points of gas detection). For very large systems, PLCs have the advantage of scaling fairly inexpensively to accommodate large point counts. PLCs offer the added benefit of extensive connectivity options for communicating with other DCS or ESD systems.

Controller-based gas detection lends itself to small to medium sized systems very effectively. A controller-based gas detection system is relatively easy to implement, and does not require software programming tools. The hardwired nature of a controller-based solution makes it inherently simple to troubleshoot and support.

What is the difference between fail-safe operation and the supervision requirements of the fire codes and NFPA 72?

The underlying principle of fail-safe design assumes that a process or item of equipment can be designed to take the process to a safe status on equipment failure or power interruption. This approach requires that the switch to “safe state” be possible without power and that the “normal operating state” of the equipment utilize energized control circuits.

Almost all detection, extinguishing and notification circuits of a Fire Alarm system are not normally energized and are not “fail-safe”. In order to be sure these fire circuits are intact and ready for use when needed these circuits are “supervised”. Supervision is normally done using a small current or voltage passed through a field circuit device called an “end of line device”. This small current or voltage is continuously monitored to verify that the circuit is intact and ready for operation.

Fire Alarm systems in many cases need to activate suppression or notification equipment in the event of a hazardous condition and these systems require power be available to do so. This is the primary arguments behind the NFPA 72 requirements associated with backup power systems and batteries.

Should we take addressable fire alarm communications in to process areas?

Addressable fire alarm communication devices can be used in process areas when the operating specifications of the devices are compatible with the electrical and environmental conditions found in these process areas.

Most commercial addressable fire alarm equipment are normally rated for operation in general purpose environments with ambient temperatures between 0 and 50°C. Most process area environments have operating temperature ranges outside the 0-50°C range. Many process area environments require devices suitable for Division 1 or Division 2 areas.

When using commercial addressable fire alarm equipment we normally recommend that the addressable equipment be located only in environmentally controlled areas such as crew quarters, control rooms, office areas. If devices to be connected to the addressable fire alarm system are to be located outside these environmentally controlled areas, we recommend the use of an addressable to conventional circuit converter to be installed inside the environmentally controlled area with a conventional circuit interface to the process area located device.

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