Fire & Gas Detection

Quick pick (TL;DR)

Match detector to hazard: hydrocarbon gas → IR point (no poisoning) or open-path IR for wide areas; H₂/some gases → catalytic; toxic (H₂S, CO) → electrochemical (ppm); fire → UV/IR flame, plus smoke/heat indoors.
Lay out for ≥ 90% geographic coverage (or scenario/dispersion mapping).
Use 2ooN voting to confirm before tripping.
Set 20% LEL alarm / 40% LEL executive action (ESD, deluge) and design the F&G to the required SIL.

Step 1 — Detector by hazard

Hazard	Detector	Why
HC gas	IR point / open-path	No poisoning
H₂ / others	Catalytic	IR blind to H₂
Toxic	Electrochemical	ppm sensitivity
Fire	Flame + smoke/heat	Flame & smoke

Step 2 — Coverage & action

HC gas area layout

Step 1 — Detector & coverage HC gas → IR point detectors geographic coverage target ≥ 90% point radius ~5–7 m → grid to cover area Step 2 — Voting 2ooN to confirm before executive action 1ooN for alarm (sensitive) Step 3 — Action levels 20% LEL → alarm (investigate) 40% LEL (2ooN) → ESD + deluge Step 4 — Integrity F&G logic to required SIL (IEC 61511)

Coverage (not fixed spacing) drives layout; 2ooN voting avoids false trips; two-stage alarm/trip.

Step 3 — Integration & integrity

F&G is a safety system — design to SIL.
Cause-and-effect matrix for actions.
Ex-rated; open-path for large areas.

Common mistakes

Catalytic where it gets poisoned.
Fixed spacing → blind spots.
1ooN on executive action.

Requisition & datasheet

Hazard, detector, range, coverage.
Voting, levels, action, SIL.

Frequently asked questions

What should I know about Fire & Gas Detection?

Match detector to hazard: hydrocarbon gas → IR point (no poisoning) or open-path IR for wide areas; H₂/some gases → catalytic; toxic (H₂S, CO) → electrochemical (ppm); fire → UV/IR flame, plus smoke/heat indoors. Lay out for ≥ 90% geographic coverage (or scenario/dispersion mapping). Use 2ooN voting to confirm before tripping. Set 20% LEL alarm / 40% LEL executive action (ESD, deluge) and design the F&G to the required SIL.

Which standards or codes apply?

IEC 60079-29 (gas detectors), ISA 84 / IEC 61511 (F&G integrity), NFPA 72 (fire alarm), EN 50402, ISA TR84.00.07 (F&G effectiveness).

Standards — IEC 60079-29; ISA 84 / IEC 61511; NFPA 72.