Deciding quota pricing of combustible gas alarms across systems: the split between the industrial-instrument "safety monitoring device" (per set) and the fire "point-type detector" (per unit), the code basis and the unit difference

Topic Positioning

The system attribution and item selection for combustible gas alarms (combustible gas detectors) in quota and bill pricing - the split between the industrial instrument basis (safety monitoring device, per "set") and the fire basis (point-type detector of the automatic fire alarm system, per "unit") - and the audit consequences of borrowing quotas across systems. For cross-discipline pricing disputes, settlement review and tender price ceiling compiling.

Core Conclusions

1. The gauges (all three must match) (1) system attribution: which controller receives the signal (DCS / PLC or the fire alarm panel); (2) device make-up: a lone sensor head, or head plus combustible gas alarm controller as a set; (3) whether the quota item's unit and work content match the works.

Scenario	Owning system	Pricing basis	Unit	Work content
Gas alarms on industrial plants, process piping and reactors, signals to DCS / PLC for process interlocks (feed cut-off, emergency shutdown)	automatic control instruments (instrument discipline, "industrial plant" system)	safety monitoring device - combustible gas alarm	set	counting, unit checks, adjustment, installation, system test (integral head plus alarm installation and commissioning)
In civil / building works, signals to the fire alarm panel, used only for warning and fire interlocks	fire protection (automatic fire alarm system)	point-type detector - combustible gas	unit	wire check, tinning, base and head installation, addressing, cleaning, testing (in-situ commissioning)

2. Code basis (why the fire point-type default is wrong) GB 50116-2013 Code for Design of Automatic Fire Alarm Systems, clause 8.1.2: "the combustible gas detection and alarm system shall stand alone, and combustible gas detectors shall not connect into the detector loops of the fire alarm panel; where the gas alarm signal must enter the automatic fire alarm system, it shall be brought in through the combustible gas alarm controller." Clause 8.1.1: "the combustible gas detection and alarm system shall comprise the combustible gas alarm controller, combustible gas detectors and audible-visual fire alarms" (giving early warning at gas concentrations below the lower explosive limit). The commentary gives four reasons: (1) gas detectors draw tens of milliamps, loading the bus unfavourably; (2) service life is only 3-4 years, after which they impair the fire detectors on the same bus; (3) annual calibration disturbs the same-bus fire detectors; (4) gas and fire alarm signals differ in timing and meaning and are handled differently. The system needs independent power, with supply reliability equal to the system's when tapped locally.

• With both the system make-up and the signal handling different, "both are called combustible gas" is no ground for interchangeable pricing.

3. The bill (measurement standard) bases also run in parallel, split by scenario GB/T 50856-2024 Annex J table J.4.1 (automatic fire alarm system, code 030904), note 3: "point-type detectors include flame, smoke, heat, infrared beam and combustible gas detectors"; note 1: "the conduits, wiring and junction boxes of fire alarm systems list under Annex D electrical equipment installation"; note 5: "cabinets are bare; devices within list under the corresponding items". GB/T 50856-2024 Annex K table K.6.1 (gas appliances and others, code 031006), note 5: "combustible gas detection alarms and solenoid valves list under the corresponding items of Annex K.2 pipe attachments" - a third port (as pipe attachments) in the gas-works context. Notes 2 and 4 of the same J.4.1 group (fire PA and telephone hosts including amplifiers, recorders, distributors, control cabinets; fire bells coded as audible-visual alarms) help bound the listing of set equipment.

4. Quota comparison (two bases within one standard, order-of-magnitude gap) DB11/T 2382-2024 as the example:

• Instrument basis (section 6.6 automation and control instruments, VI safety, video and control systems; Annex C table C.6.21 safety monitoring devices): item C6-5-1 "combustible gas alarm", unit "set", work content "counting, unit checks, adjustment, installation, system test etc.", labour 1.6250 workdays (all-in Grade II), with multi-function signal calibrators, precision resistance boxes, motorised calibration benches and radios; clause 6.6.31 item 6 states "combustible and multi-point gas alarms shall include the integral installation and commissioning of head and alarm"; 6.6.33 "safety, video and control systems are preferably compiled as complete sets", quantities by design-shown count.
• Fire basis (Annex G urban rail transit, table G.6.13 point-type detector installation): item G6-3-5 "conventional-wiring point-type detector, combustible gas", unit "unit", work content "wire check, tinning, base and head installation, addressing, cleaning, testing", labour 0.2260 workday.
• The two differ by over seven times (1.6250 / 0.2260 is about 7.2; the gap widens once the instrument items band by size), and with the set alarm hardware and system test on top, the all-in rates differ markedly. (DB11/T 2382-2024 chapter 6.9 automatic fire alarm carries items 6.9.42 to 6.9.49 of the fire basis, coexisting with the 6.6 instrument basis in one standard.) Corroborating: TB/T 10829-2024 Railway Works Budget Quota Manual, Volume 8 power works, automatic systems - automatic fire alarm, lists "field detector installation and commissioning, combustible gas type" (DY-1290) per "unit", smoke and heat types alike - the "into the fire alarm system, per unit" route.

5. Audit conclusion Writing the instrument basis down to fire point-type detectors (or the reverse) is mis-application or unsupported cross-system borrowing; without design support (which controller the signal enters, whether used for process interlocks) it is unbased and refutable on GB 50116-2013 clause 8.1.2 and the quota chapter notes.

Applicability Boundaries

• The decision must return to the design documents and system diagrams: which controller the signal enters, process interlock use, set or lone head. Neither "same name" nor "dearer basis wins" is admissible.
• A stand-alone gas detection and alarm system inside a civil building (signals not entering the panel's detector loops) remains an independent subsystem - its civil setting does not automatically make it a fire point-type detector.
• Regional and sector quotas differ in volume / chapter splits and item names (DB11/T 2382-2024 sets 6.6 instruments apart from 6.9 fire; TB/T 10829-2024 lists under Volume 8 power); item codes, units and bands follow the executed quota text and its companion on-cost quota - this card does not replace them.
• Where the quota lacks an item, do not borrow across volumes at will - compile a supplementary unit-rate build-up schedule / supplementary quota per the quota principles and submit for approval; cross-sector reference (railway borrowing municipal, local borrowing national) needs separate justification on record.
• This card decides the pricing basis only and carries no regional labour, material or plant prices; factor prices in rate build-up follow the compiling-period market.

Further Reading

• GB 50116-2013 Code for Design of Automatic Fire Alarm Systems, chapter 8, clauses 8.1.1 and 8.1.2 and commentary (system make-up, the four reasons for independence, independent power).
• GB/T 50856-2024 quantity take-off standard for general building services: Annex J table J.4.1 (030904), notes 1, 3, 5; Annex K table K.6.1 (031006) note 5; the corresponding items of Annex K.2.
• DB11/T 2382-2024 Construction Works Consumption Quota Standard: clauses 6.6.30 to 6.6.34 (safety, video and control systems; gas alarms including integral installation and commissioning; preferably compiled as sets) and 6.9.42 to 6.9.49 (automatic fire alarm); Annex C table C.6.21 item C6-5-1 (unit set); Annex G table G.6.13 item G6-3-5 (unit per piece).
• TB/T 10829-2024 Railway Works Budget Quota Manual, Volume 8 power works: automatic systems - section 2 automatic fire alarm, DY-1289 to DY-1321 (DY-1290 combustible gas type, unit "unit").
• At review level, apply the "three-way check": the works as built (drawings / method statement) against the item's work content against the chapter notes and measurement rules - focussing on cross-volume borrowing and duplicated work content.