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Back to: Advanced Physical Security Integration (APSI)

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Lesson 6.3: The Fire Alarm Interface (FAI)

Module: 6 – Unified Integration Logic

Prerequisites: Lesson 6.1 (Relays) & Lesson 4.3 (Life Safety)

Estimated Time: 45–60 Minutes

1. Learning Objectives

By the end of this lesson, you will be able to:

  • Interpret NFPA 72 and Life Safety Code requirements for unlocking doors during a fire.
  • Compare the two methods of FAI: Power Supply Cut (Hardware) vs. Input Trigger (Software).
  • Explain why software-based unlocking is generally not code compliant for maglocks.
  • Wire a supervised latching relay system that requires a manual reset after a fire alarm.

2. The Code Requirement (NFPA 101 / 72)

When a fire alarm pulls, or a smoke detector trips, all Fail-Safe locking devices (Maglocks) on the egress path MUST unlock immediately.

The Three Critical Rules:

  1. Immediate: No delays. No “wait 3 seconds.”
  2. Positive Release: The release must be a physical cut of power, not dependent on a computer processor making a decision.
  3. Latching (Manual Reset): If the fire alarm silences (e.g., the strobes stop flashing), the doors must NOT automatically re-lock. A human must physically go to the access panel and push a button to re-secure the building.
    • Why: The fire might flare up again, or firefighters might still be moving through.

3. Method 1: The “Power Cut” (The Right Way)

This is the industry standard for Maglocks.

The Hardware:

  • Fire Panel (FACP): Provides a Dry Contact Relay (NC) that opens on alarm.
  • Access Power Supply: Most modern power supplies (e.g., Altronix, LifeSafety Power) have a dedicated “FAI Input” terminal.

The Wiring:

  1. Run a 2-conductor cable from the FACP Relay to the FAI Input on your Power Supply.
  2. Set the Power Supply logic to “Cut Power on Open”.
  3. Wire all Maglocks to the power supply outputs.

The Sequence:

  • Fire: FACP Relay Opens -> FAI Input triggers -> Power Supply physically cuts 12V to all lock outputs -> Doors Open.
  • Benefit: It is bulletproof. Even if the Access Controller processor is fried or frozen, the power supply cuts the voltage.

4. Method 2: The “Input Trigger” (The Wrong Way)

Warning: Many inexperienced integrators do this, and inspectors will fail you.

The Scenario:

You wire the Fire Alarm into an Input on the Access Controller (e.g., Input 1).

You program the software: “If Input 1 = Active, Then Unlock All Doors.”

Why it fails code:

  1. Dependency: It relies on the processor. If the controller is rebooting or the firmware crashes during the fire, the doors stay locked.
  2. Latency: Software logic takes milliseconds to process. Code usually requires instantaneous electromechanical release.
  3. Verdict: Acceptable for “Free Egress” doors (Electric Strikes), but Illegal for Maglocks in most jurisdictions.

5. Latching Logic & Reset

After the fire department gives the “All Clear,” how do you lock the building?

Key Switch Reset:

  • The Problem: The Fire Panel resets automatically when the smoke clears. If your power supply follows the fire panel, the doors lock immediately.
  • The Solution: The FAI logic on the Power Supply should be set to “Latch”.
  • The Reset: You install a physical Key Switch (or button) next to the power supply. The Security Director must walk to the closet, verify the building is empty, and turn the key to reset the FAI and re-energize the magnets.