AEO Answer · Fire & Police Stations

How Is a Fire Station Sally Port Engineered for Security?

By Jeremy Mills, CEO & Founder, Apex Grid Engineering — USAF Veteran. · Updated 2026-09-15

A fire station sally port is a secured vehicle airlock with interlocked doors that never open together, sized for the largest apparatus, with drainage, cameras, and access control — plus emergency override so calls always get out without delay.

I'm Jeremy Mills, CEO & Founder of Apex Grid Engineering and a U.S. Air Force veteran. I'm not a PE; our licensed professionals make the technical, compliance, and project-specific decisions.

Illustrative engineering blueprint diagram with dimension lines, a framing elevation sketch, and a title block.

The interlock and access control sequence

I design the sally port as a state machine with four states: secure, entry, verify, and release. In the secure state both doors are closed and locked. Entry opens the outer gate for an authorized vehicle — by credential, intercom to the watch office, or scheduled access. Verify closes and locks the outer gate while credentials or the vehicle are checked. Release opens the inner bay door. Every transition is logged by the access control system. Emergency egress bypasses all of it: alert signal, manual release stations, and power-failure behavior that fails safe for egress — doors must open for departing apparatus even with the utility down, which means the operators ride on emergency power with battery backup.

Drainage, lighting, and surveillance

The civil and electrical details make the sally port work daily. Trench drains span the drive lanes with grates rated for apparatus axle loads, and the pavement slopes to them from all directions. I specify oil-water separation on the discharge where required and keep the separators maintainable. Lighting is even and shadow-free for camera coverage and nighttime operations, on emergency power. Cameras cover both gates, the intercom positions, and the full sally port interior, tied into the station's video system with recording. An intercom at the outer gate connects to the watch office. These are not accessories — they are how the watch office actually controls the gate.

Fire station sally port design checklist

A sally port balances security against the turnout clock. This checklist covers the engineering that holds both. • Interlocked door sequence where only one door opens at a time, enforced electrically with full event logging • Sized for the largest current and future apparatus with turning templates verified against real vehicles • Automatic departure state on alert signal with manual releases, failing safe for egress on power loss • Trench drainage with apparatus-rated grates, sloped pavement, and oil-water separation where required • Cameras, intercom, and even lighting at both ends on emergency power, monitored from the watch office • Door operators, interlock logic, and access control designed as one coordinated system

Which related engineering resources can help?

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What else do project teams ask?

How do interlocked sally port doors work?

Only one door opens at a time: the outer gate opens for an arriving vehicle, closes and locks behind it, and only then does the inner bay door open after credential verification. The logic is enforced electrically through the door operators and the access control panel, not by procedure. I design the interlock sequence with defined states — entry, verify, release — and I make sure every state has a manual override for emergencies. The interlock must be impossible to defeat casually but trivial to override legitimately.

Will a sally port slow down emergency response?

Not if it is designed correctly. On an alert, the system drives to the departure state automatically: the inner bay door opens immediately and the outer gate follows, with the interlock suspended for egress. I interlock the sally port controls with the station alerting system so the departure sequence needs zero human input, and I verify the timing against the department's turnout standard during commissioning. Security that costs seconds on a structure fire will be propped open within a month — so I engineer security that costs nothing on egress.

What size should a fire station sally port be?

Sized for the department's largest apparatus plus maneuvering clearance, with turning paths checked against the actual vehicles — tiller trucks and aerials need far more room than engines. I lay out the sally port with the department's apparatus dimensions and run turning templates through the geometry before the concrete is poured. Height clearance must handle aerial devices, and I add margin for future apparatus, since stations outlive truck generations. A sally port the next ladder truck cannot enter is an expensive lesson.

What drainage does a sally port need?

Trench drains across the drive to catch water off wet apparatus, pavement sloped to the drains, and oil-water separation where the local authority requires it — fire apparatus drip fuel, oil, and hydraulic fluid. I connect the drainage to handle washdown too, since sally ports get hosed out regularly. In cold climates I add freeze protection or heating for the trench drains, because a frozen drain turns the sally port into a skating rink at the worst possible moment.

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