Detection & Alarms

Detection & Alarms covers the instruments that sense a hazard on a rig and raise the alarm: fixed flammable gas and hydrogen sulphide (H2S) detectors, flame, smoke and heat detectors with their fire and gas panels, and personal gas monitors.

The fixed items work as one system under an approved cause and effect logic. A used detector therefore has to match your panel, your hazardous area zoning and your class approval, not just the gas it measures.

How the three sub-Categories differ

Sub-Category	What it senses	Where the signal goes
Gas and H2S detection	Flammable gas in %LEL, H2S in ppm, sometimes oxygen	Fire and gas panel or safety PLC
Fire detection systems	Flame radiation, smoke, heat, manual call points	Fire and gas panel or fire alarm panel
Portable gas detectors	Two to five gases at the wearer's breathing zone	The wearer, through alarms, and a docking station log

Fixed detection protects an area around the clock and can act without a person. It closes dampers, trips ventilation, isolates ignition sources and starts deluge. A personal monitor protects one person and goes into places the fixed heads never see, such as a tank or a mud pit before entry. You need both, and a class surveyor treats them separately.

Hazardous area marking across the group

Every fixed head and every personal monitor used in a classified area carries an explosion protection marking. Read it before anything else.

Zone suitability, shown as an equipment protection level (EPL Ga, Gb or Gc for Zones 0, 1 and 2).
Protection concept, such as Ex d (flameproof), Ex e (increased safety) or Ex ia (intrinsic safety).
Gas group IIA, IIB or IIC. IIC covers hydrogen and acetylene and is the safe default offshore.
Temperature class T1 to T6. T4 or better suits most hydrocarbon service.

ATEX marking follows EU Directive 2014/34/EU. IECEx certificates can be checked in the public IECEx online database by certificate number. North American equipment may carry Class I, Division 1 or Zone listings under the NEC instead. A unit without a legible nameplate or a traceable certificate cannot go back into a hazardous area.

Standards that apply to the whole group

IEC 60079-29-1 sets the performance requirements for flammable gas detectors. IEC 60079-29-4 does the same for open path detectors.
IEC 60079-29-2 gives the rules for selecting, installing, using and maintaining them.
EN 45544 covers detectors for toxic gases such as H2S and carbon monoxide.
The EN 54 series covers fire detectors, panels and power supplies.
The IMO Fire Safety Systems (FSS) Code, Chapter 9, governs fixed fire detection and alarm systems on vessels and many mobile offshore units.
DNV-OS-D301 and the matching ABS rules set fire and gas detection requirements for classed offshore units.
IEC 61508 and IEC 61511 apply where the fire and gas system performs safety instrumented functions with a SIL target.

What ages on the shelf

The electronics and enclosure of a detector can last decades. The sensing element cannot.

Sensor	Ages by	Treat a surplus unit as
Electrochemical (H2S, CO, O2)	Electrolyte drying and consumption, even unpowered	Needs a new cell
Catalytic bead	Poisoning by silicones, lead and some lubricants	Needs a new sensor if history is unknown
Infrared	Optics fouling, source drift	Usable after cleaning and calibration
Metal oxide semiconductor	Drift without heater power	Needs a full calibration and response test
UV and IR flame	Window contamination, UV tube wear	Needs window cleaning and a test lamp check

Treat every sensor of unknown date on a used or surplus detector as a consumable. Budget for new cells, certified calibration gas with a valid expiry date, and the calibration kit the maker specifies.

Integration questions that cut across the group

Replacing a head is simple only when the signal and the logic are unchanged. Check these before you commit.

Output. A 4 to 20 mA signal, with or without HART, connects to most panels. Addressable loop devices usually work only with the same maker's panel.
Fault signalling. Many detectors indicate a fault below 4 mA, often to NAMUR NE 43 levels, and your panel must read that as a fault rather than zero gas.
Supply voltage and power draw. Flameproof IR and flame detectors with heated optics draw more than a catalytic head.
Cable entries. Thread type (metric or NPT) and the certified gland or stopping plug must match the enclosure.
Cause and effect. A different detector type can change voting, alarm levels and response time, so the safety case and the class approval may need updating.

Sourcing used detection equipment

Panels, flameproof enclosures, flame detectors and IR heads from a decommissioned rig often have years of life left. Spares for a system the maker no longer builds are the strongest reason to look at used units. Never reuse a sealed disposable monitor, an expired electrochemical cell or any sensor without a manufacture date.

Ask for the model and part number, the Ex certificate, the type approval, the last calibration record and, for panels, the software version and cause and effect. Naventr can pass your questions to the Seller and arrange an independent inspection on request.

FAQ

Frequently asked questions

Is it safe to buy used gas detectors for an offshore rig?

Yes, provided the enclosure, electronics and Ex certificate are sound and you fit new sensors and recalibrate before service. Sensors are the wearing part, so treat a used detector as a body that needs re-sensoring. Never put one into service on its previous calibration.

What certification do gas and fire detectors need offshore?

Detectors in hazardous areas need ATEX or IECEx certification for the zone, gas group and temperature class, or a North American Class and Division listing. Flammable gas detectors are performance tested to IEC 60079-29-1. Classed units usually also need DNV, ABS or equivalent type approval.

Can I mix detectors from different manufacturers on one fire and gas panel?

Often yes, when the detectors use a standard 4 to 20 mA or relay output. Addressable devices on a proprietary loop generally work only with that maker's panel. Check the panel's approved device list, the fault current levels and the class approval before mixing brands.

Fixed or portable gas detection, which do I need?

You need both, because they cover different risks. Fixed heads watch an area continuously and can trigger shutdowns through the panel. Personal monitors protect each worker during confined space entry, hot work and tasks away from the fixed heads.

Which detection items should never be bought used?

Never buy used disposable single-gas monitors, expired electrochemical cells or calibration gas past its expiry date. Their remaining life cannot be restored or verified. Enclosures, panels and optical detectors are different, since a calibration and function test can prove them.

Looking for detection & alarms?

Tell us what you need and we will find out what is available. We reply within one business day.

Enquire