For permit-required confined space entry in 2026, the minimum defensible instrument is a 4-gas pumped portable covering O2, combustible gas (LEL), carbon monoxide, and hydrogen sulfide, with an optional fifth channel for CO2 or a specific toxic [S1][S4].
The 5-gas pumped portable has become the practical default: Crowcon's Gas-Pro lists 43 x 130 x 84 mm and 309 g (4-gas) to 362 g (5-gas pumped), an IP65/IP67 housing, audible alarm rated >95 dB at 30 cm, and 14 hr run-time from a 7.5 hr Li-ion charge, with 125 hr of data logging at 10-second intervals (45,000 logs) [S1]. The competing MP400S / MP400 / MP400P line from mPower (VeerTek) covers the same four core gases plus optional CO2 and VOC via PID, in diffusion or pumped versions aimed at confined-space compliance [S4].
Sensor Stack: What the Four-Gas Baseline Actually Covers
The four-gas baseline is anchored on the dominant atmospheric hazards: oxygen deficiency/enrichment, combustible atmospheres above the lower explosive limit, and the two toxic asphyxiants most frequently present in sewer, tank, and refinery work, namely CO and H2S [S1][S4]. Electrochemical cells drive the CO and H2S channels, a pellistor (catalytic combustion) handles LEL combustible gas, and a lead-free electrochemical or galvanic cell covers O2; this sensor mix is the de-facto stack written into most plant CSE (confined space entry) procedures [S4]. The Chinese occupational-health reference standard GBZ/T 222-2009 (Guideline for selection of direct-reading gas detector in the confined space) explicitly recognises both catalytic-combustion and infrared sensing principles for this application, alongside reference to GB 12358, GB 15322.3, GB 3836.1, GB 50058, GBZ 2.1, GBZ/T 205, and GBZ/T 206 as the related detector and hazardous-area frameworks [S2].
For a fifth or sixth channel, the technology choice follows the target gas. MP400S supports a full range of sensor types in a pumped package: electrochemical (EC) for H2S/CO, pellistor for LEL, non-dispersive infrared (NDIR) for CO2, and photo-ionization detector (PID) for volatile organic compounds (VOCs) [S4]. Crowcon's Gas-Pro adds ammonia, chlorine dioxide, ozone, and sulfur dioxide as additional toxic options on the same physical platform [S1]. NDIR is the right call for CO2 in confined spaces where pumped sampling matters, because it does not consume O2 like a chemical cell would; PID is the right call when solvent or fuel vapour is the suspected contaminant.
Pumped vs Diffusion and the Pre-Entry Check
A diffusion-only monitor is not a substitute for a pumped pre-entry test. Crowcon's Gas-Pro integrates an optional internal pump "activated with the flow plate" that lets the same instrument work in pumped pre-entry mode and then switch to belt-worn diffusion mode during work; the unit auto-recognises the flow plate as a fail-safe against the operator forgetting to switch modes [S1]. This dual-mode packaging is the single most useful feature for CSE work, because the pre-entry test must sample from a remote point (the manhole or tank opening) while the worker is still in fresh air, and then the same instrument must clip to the worker in diffusion mode during the entry.
MP400 and MP400P are explicitly offered in both "diffusion or pumped versions" for confined-space-entry compliance, with the pumped model matched to the same Pre-Entry Check workflow [S4]. GBZ/T 222-2009 distinguishes pumped ("aspirating") and diffusion direct-reading instruments in its selection guidance, which is the regulatory reason both physical form factors continue to ship side-by-side rather than one replacing the other [S2]. For most plant operations, specifying a single pumped unit with auto flow-plate recognition is simpler than managing two fleets.
Alarm, Ruggedness, and Run-Time Thresholds
The audible alarm output of a CSE-grade portable is not negotiable: Gas-Pro is rated >95 dB at 30 cm (98 dB in loud mode), with a visual alarm using all-angle dual red/blue LEDs and a vibrating alert [S1]. High-noise work sites (refineries, compressor stations, paper mills) routinely need the loud mode, and the 360° visual LED is what a stand-by attendant watches when the worker is already inside the space.
Ingress protection should be at least IP65, with IP67 as the practical target for wash-down and submerged-mud conditions. Gas-Pro is rated IP65 and IP67 [S1]. Run-time is the other common fail-mode: lithium-ion battery delivering over 14 hours from a 7.5-hour charge covers a 12-hour shift plus a top-up charge at lunch [S1]. For multi-shift plants, hot-swap battery capability or a guaranteed second-shift runtime on the same charge should be added to the spec, because a detector that goes flat mid-entry is itself a confined-space incident.
Calibration, Bump Testing, and Data Logging
Bump-test and calibration discipline is the area where fleets fail in practice, not sensor technology. Gas-Pro is supported by the I-Test bump test and calibration station, with the detector itself providing "bump and calibration reminders" for full compliance tracking [S1]. The platform logs 125 hours at 10-second intervals, which is 45,000 data points, plus 1,000 event entries (alarm, over-range, calibration, bump, on/off, TWA) for incident reconstruction [S1].
For a procedure-driven buyer, three specifications matter: (1) automatic bump-test station compatibility (so the fleet cannot be returned to service without a pass), (2) on-device reminders that block arming when a bump is overdue, and (3) tethered or wireless data download for incident reporting. Missing any one of these converts the gas detector from a safety instrument into a compliance prop. Dräger's CSE guidance explicitly routes the monitoring step into the permit-to-work process, so the instrument's data trail must reconcile with the paper or digital permit that authorised the entry [S3].
Comparison: 4-Gas vs 5-Gas vs 6-Gas for Real CSE Work
The four-gas pumped portable (O2, LEL, CO, H2S) is the right specification when the space is a sewer, potable-water vault, or refinery vessel with documented history, because the toxic and asphyxiant profile is bounded and the cost-per-unit matters across a 50- or 100-instrument fleet. The five-gas build (adding CO2 or NH3) is justified for brewery and fermentation work, dry-ice storage, CO2 fire-suppression system rooms, and agricultural or wastewater digesters where ammonia stripping is documented; NDIR for CO2 is the technology choice here, and a Gas-Pro / MP400S-class unit absorbs the fifth channel in the same housing at the same ingress rating [S1][S4]. The six-gas build (typically adding a PID for VOC) is the right specification for petrochemical, paint-booth, pharmaceutical, and solvent-recovery work where benzene, toluene, or xylene can reach IDLH concentrations before the LEL sensor sees a problem [S4].
Decision criteria in a procurement matrix: (a) pumped pre-entry capability with auto flow-plate recognition, (b) sensor count and technology match against the documented atmospheric hazard inventory, (c) IP65/IP67 ingress rating, (d) ≥14 hr Li-ion runtime, (e) ≥95 dB alarm plus 360° visual plus vibration, (f) automatic bump-test station support with on-device reminders, (g) ≥125 hr data logging at 10-second intervals. A unit that meets all seven is procurement-grade for a permit-required CSE program.
Selection Triggers: When to Walk Away From a Detector
A detector that is diffusion-only with no pumped option, or that requires a manual flow-plate, is the wrong tool for permit-required CSE work because the pre-entry test cannot be performed reliably with a diffusion sensor at the manhole [S1][S4]. A detector without an audible alarm rating at or above 95 dB at 30 cm is the wrong tool for any high-ambient-noise site (the loud-mode rating of 98 dB on Gas-Pro is the practical minimum in compressor stations and paper mills) [S1]. A detector without bump-test reminders, or one whose reminders can be bypassed by the operator, is the wrong tool for any fleet that has to pass an external audit, because the data trail will not reconcile with the work permit [S1][S3]. Finally, a detector whose Li-ion battery is not user-replaceable in the field is the wrong tool for multi-shift plants, because a dead instrument mid-shift becomes a confined-space incident in its own right.
Standards Stack and Sourcing Path
The applicable published standards framework covers the device, the application, and the hazardous area. On the device side, GBZ/T 222-2009 is the dedicated Chinese selection guideline for direct-reading gas detectors in confined spaces, and it references GB 12358 (gas detectors in general), GB 15322.3 (combustible-gas detectors), GB 3836.1 (explosive atmospheres - general requirements), and GB 50058 (explosive atmospheres electrical installation design) [S2]. The companion standard GBZ/T 206-2007 covers direct-reading instrument gas detection in confined spaces, and GBZ/T 259-2014 covers hydrogen sulfide occupational hazard protection; the T/AHPAWS 02-2021 limited-space safety management specification cites GBZ/T 222-2009 directly [S2].
On the application side, OSHA-style permit-required confined space programs in the United States and equivalent national programs elsewhere treat the gas detector as a control element in the entry permit, not as a stand-alone instrument, and the permit must reference the same monitoring, alarm, and rescue chain that the detector supports [S3]. Dräger's CSE guidance routes the monitoring step into the same risk-assessment and permit-to-work process that controls the rest of the entry [S3]. For an aligned warehouse and storage-fleet specification that parallels CSE logic but covers less toxic atmospheres, see the spec map in warehouse gas detector selection. For complementary sensor-class logic in arc-flash-adjacent work, see gas detector selection for electrical work. For a hot-work CSE-adjacent scenario with a different sensor mix, see gas detector specs for welding operations.
The baseline cross-reference for the four-gas portable is the portable gas detector family page, with the multi-gas detector entry covering 4-gas-and-up common build, the combustible gas detector entry covering the LEL pellistor technology, the toxic gas detector entry covering the CO and H2S electrochemical cells, and the fixed gas detector entry covering the permanently-mounted complement used for area monitoring when a portable fleet is parked. Trackable next signal: publication of a revised GBZ/T 222 successor (the 2009 issue is still the active version cited in 2026 references) and harmonisation of the Chinese GBZ framework with IEC 60079-series hazardous-area rules for portable CSE equipment.