Safety Systems Built Around What Your Process Actually Handles

A chemical plant is not one hazard. It is a dozen of them sharing a fence line — a light hydrocarbon in one unit, a heavy solvent vapour in the next, a toxic gas in the third, and a hydrogen line running past all of them. Fire and gas detection designed against the site as a category rather than against the inventory as a list will always leave something uncovered.

ZE-Tronics designs, supplies and maintains detection, suppression, notification and safety control systems for petrochemical and chemical facilities, and starts from the substances the process actually handles, the conditions they are handled under, and the area classification that follows from both.

Start with the classification, not with the catalogue

Hazardous areas are classified by what is present, how much of it, and how often. NFPA 70 Article 500 divides them into Class I for flammable gases and vapours, Class II for combustible dust and Class III for ignitable fibres and flyings, each split into Division 1 and Division 2. Article 505 offers the Zone system aligned with IEC 60079 — Zone 0 where a flammable atmosphere is present continuously or for long periods, Zone 1 where it is likely in normal operation, Zone 2 where it is unlikely and short-lived.

That classification decides everything downstream: which protection concept the equipment must use, which temperature class it must carry, and which certificate is acceptable. Electrical equipment is itself an ignition source, so where it cannot be kept out of the classified area it has to be explosion-proof, purged and pressurised, or intrinsically safe. We work in both the Division and the Zone systems and will state plainly which one a given certificate satisfies.

Gas detection matched to the inventory

Gas detection is the first line of defence, because it warns before there is anything to ignite. Which technology to use is a per-area decision, not a site-wide one.

• Point infrared — stable, immune to poisoning, fails safe on optics, and the default for hydrocarbon service. It cannot detect hydrogen.
• Catalytic bead — detects effectively every known combustible gas including hydrogen, at the cost of drift and vulnerability to silicone and sulphur poisoning. Specified with dust caps or flame arrestors where the environment demands it.
• Electrochemical — for toxic gases: hydrogen sulphide, ammonia, chlorine, carbon monoxide and process-specific species.
• Open-path infrared — a continuous beam across a corridor, a perimeter or a loading area. A complement to point detection, not a replacement for it.
• Ultrasonic — hears a pressurised release directly, which matters where ventilation would disperse a cloud before it reached a sensor.

Placement follows the gas, not the drawing. Vapours heavier than air collect in pits, trenches, sumps, bunds and under equipment skids; detection mounted at head height will report clean air while a flammable layer builds below it. Lighter gases do the reverse. Toxic detection is placed where people breathe; combustible detection is placed where an ignitable accumulation forms. They are rarely the same height.

Flame detection where speed decides the outcome

Where a fire develops fast and the consequence of a delayed response is severe, radiant energy detection is specified alongside gas detection. NFPA 72 lists what has to be considered when selecting and siting flame detectors: the size of fire to be detected, the fuel involved, detector sensitivity and field of view, the distance between fire and detector, atmospheric absorption of radiant energy, and the presence of external radiation sources that could cause a false alarm.

That last point is what separates a working installation from a disabled one. A plant with flare stacks, hot surfaces, arc welding and direct sun has plenty of sources that look like fire to a poorly chosen detector. Multi-spectrum infrared and UV/IR combinations exist precisely to discriminate between them, and we select and orient detectors so the system keeps its credibility.

Suppression, notification and shutdown

Detection has to lead to action. We engineer the release logic as carefully as the detection layout — confirmed voting arrangements so a single sensor fault cannot dump an agent, clear manual override, and interfaces to the process shutdown and emergency shutdown hierarchy that are documented and testable.

• Clean agent suppression for control rooms, analyser houses, MCC and electrical rooms
• Foam and water spray for tanks, bunds, pump areas and loading racks
• Ex-rated beacons, sounders and voice notification sized for the actual noise level
• Cause-and-effect matrices developed with operations, not handed to them
• Hardwired trips where the action must not depend on a communication link

Certified equipment, verified performance

Third-party certification matters more in this sector than almost any other. A manufacturer’s self-declaration says the product met an internal test; an accredited certification body’s mark says an independent laboratory verified it. For performance, that means FM, UL and other nationally recognised testing laboratories; for functional safety, exida, TÜV Rheinland and UL. We supply original equipment from authorised manufacturer partnerships and provide the certificates against the specification, rather than an equivalent that will be argued about at handover.

Keeping it credible over its life

The failure mode of a chemical plant fire and gas system is rarely dramatic. It is a slow accumulation of bypassed loops, overdue calibrations and alarms nobody trusts. Our in-house AZS ISO/IEC 17025:2020 accredited laboratory calibrates both fixed and portable gas detection with traceable results, our electronics repair bench restores detectors and controllers in country, and our maintenance regimes are built around drift history rather than a generic calendar.

Explore our engineering and calibration services, or send us your area classification drawings for review.