If you're specifying earthquake protection for a building's gas supply, you'll encounter two fundamentally different approaches: passive mechanical shutoff valves and active electronic trigger systems. They look superficially similar — both close a gas valve when an earthquake occurs — but they work differently, respond differently, and have very different implications for reliability and compliance.

How Mechanical Shutoff Valves Work

A mechanical seismic shutoff valve uses a simple physical mechanism — typically a steel ball balanced on a pedestal inside the valve body. When shaking exceeds a certain level, the ball is displaced, trips a lever, and the valve closes. No power required. No electronics.

The appeal is simplicity. There's nothing to fail electronically, no batteries to replace, no settings to configure.

The limitations are significant, however:

• They respond to the S-waves — the damaging lateral shaking — not the earlier P-waves. By the time the valve closes, the shaking that might have ruptured a pipe has already occurred.
• They can't distinguish earthquake from other vibration. Heavy machinery, nearby construction, or a vehicle strike can trip a mechanical valve — causing unexpected gas outages with no obvious cause.
• There's no record of activations. If a mechanical valve trips while a building is unoccupied, you may not know until someone notices there's no gas. There's no way to verify when it tripped or why.
• Manual reset required. Once tripped, someone must physically attend the valve to reset it. In a building with limited access — a plant room in a basement, a remote substation — this takes time.

How Electronic Trigger Systems Work

An electronic seismic trigger uses accelerometers to continuously monitor ground motion. Rather than waiting for physical displacement to trip a mechanism, it measures acceleration directly and compares it against a pre-set threshold.

The key advantage is P-wave detection. P-waves travel faster than the destructive S-waves and arrive seconds earlier. An electronic trigger that detects P-wave acceleration can fire its relay before the damaging shaking arrives — giving connected systems a head start on shutdown.

The MK6 Earthquake Trigger Recorder fires its output relay within 10 milliseconds of the threshold being exceeded. Sensitivity is field-adjustable from 0.012g to 0.200g, so it can be calibrated to the specific environment — a hospital has different tolerance for false triggers than a heavy industrial site. A 6-digit event counter records every activation, giving building managers an auditable log of every trigger event.

Which Is Right for Your Building?

For simple, low-risk installations where gas usage is minimal and the building is easily accessible, a mechanical valve may be adequate.

For commercial buildings, multi-unit residential, hospitals, or industrial facilities — anywhere that gas runs are long, occupants can't quickly self-evacuate, or an auditable compliance record is required — an electronic trigger provides significantly better protection. The combination of P-wave detection, adjustable sensitivity, event logging, and relay outputs capable of triggering multiple connected systems simultaneously is simply not achievable with a passive mechanical valve.

See the MK6 Earthquake Trigger Recorder → or contact us to discuss the right solution for your building.