Quick answer
A facility should choose fixed detectors for continuous area monitoring and automatic alarm linkage, and portable detectors for entry checks, patrols and confined-space work — and most industrial sites need both, because the two types do different jobs. Fixed detectors watch the area around the clock and raise the alarm automatically; portable detectors verify conditions where and when people enter, and can be carried to the point of a suspected release.
What a fixed detector does
A fixed detector is installed at a chosen monitoring point and samples the atmosphere continuously, 24 hours a day. In a typical system design, the detectors report to an alarm controller, so a leak raises audible and visual alarms automatically — including overnight and in unmanned areas — and the controller can activate ventilation or interlocks as part of the site's safety plan.
Its limitation is that it is static: point count and placement are decided during layout planning, not by the detector itself.
What a portable detector does
A portable detector is hand-held or body-worn. A worker carries it to check a location before entry, to patrol for leaks, or to survey an area during maintenance. It is the standard instrument for confined-space entry checks and for verifying an atmosphere before hot work.
Its limitation is coverage: it only samples where the person carrying it is, so there is no monitoring when nobody is patrolling. Portable instruments also depend on operator discipline — charging, bump testing before use and regular calibration.
When each is the right choice
Fixed detectors are the right foundation wherever gas is used or stored continuously and areas may be unmanned — for example LPG storage areas, boiler rooms and fuel gas trains in a typical scenario. If a leak can develop at 3 a.m. with nobody on site, only fixed detection with automatic alarms can catch it.
Portable detectors answer the question a fixed point cannot — "is it safe for a person to enter here, right now?"
For the full side-by-side comparison, see our fixed vs portable detector guide for Malaysia.
Why most Malaysian plants end up with both
An alarm raised by a fixed detector is typically investigated with a portable instrument carried to the suspected release point.
Choosing only one leaves a visible gap. A plant with only portable detectors has no monitoring when nobody is present; a plant with only fixed detectors cannot verify a vessel interior before a worker climbs in. Safety reviewers and insurers generally expect both layers for gas-hazard areas.
When planning coverage, see the combustible gas detector range and gas detector selection page, and confirm placement with a layout review before ordering equipment.