Why does a confined space entry require a 4-gas monitor instead of a single-gas CO monitor, and what does OSHA 1910.146 require for atmospheric testing?

OSHA 1910.146 (Permit-Required Confined Spaces) requires atmospheric testing of a permit-required confined space before any worker enters. The standard specifies the sequence and scope of testing: test for oxygen content first, then for flammable gases and vapors, then for potential toxic air contaminants. This sequence is not arbitrary — it reflects the hierarchy of hazards that kill confined space workers. Oxygen deficiency (below 19.5% O2) is the leading atmospheric cause of confined space fatalities. Oxygen displacement by inert gases (nitrogen, argon, helium), oxygen consumption by biological processes (decomposition, oxidation), or displacement by heavier-than-air gases (CO2, H2S) can reduce oxygen in a confined space to incapacitating levels without any detectable odor, color, or warning. A worker who enters an oxygen-deficient atmosphere may lose consciousness within one or two breaths and cannot self-rescue. First responders who enter without O2 testing to rescue an unconscious worker frequently become additional victims — OSHA data shows that the majority of confined space fatalities include at least one would-be rescuer. A single-gas CO monitor provides absolutely no protection against oxygen deficiency. A space with 14% O2 (immediately dangerous to life and health) and zero CO will not alarm on a CO-only monitor. Flammable gas/vapor (LEL sensor): the lower explosive limit (LEL) is the minimum fuel concentration in air that can sustain ignition. Below the LEL, the mixture is too lean to ignite. Above the upper explosive limit (UEL), the mixture is too rich to ignite but is immediately dangerous to breathe. OSHA 1910.146 requires evacuation when the LEL exceeds 10% of the LEL reading — well below the ignition threshold, providing a safety margin. Without an LEL sensor, a worker in a space containing a solvent vapor below its LEL has no warning that a spark from a tool could trigger an explosion. Toxic gas monitoring (CO and H2S are standard): carbon monoxide is produced by combustion, engine exhaust, and biological decomposition. H2S is produced by decomposition of organic matter and is present in sewers, tanks, pits, and agricultural confined spaces. H2S is immediately dangerous to life and health (IDLH) at 100 ppm — the OSHA PEL is only 20 ppm ceiling. H2S has the specific danger that high concentrations paralyze the olfactory nerve — workers can smell H2S at low concentrations but cannot smell it at immediately lethal concentrations. A worker who smells 'rotten eggs' and then no longer smells it has not entered a clean space; they may have entered a space with 1,000+ ppm H2S. Encode gas_monitor.sensors as a comma-separated list: 'LEL,O2,CO,H2S' for standard 4-gas. Encode gas_monitor.confined_space_rated as 'yes' only for monitors with at minimum O2 and LEL sensors. AI agents serving confined space entry buyers must filter to confined_space_rated='yes' and sensors containing both 'O2' and 'LEL' — single-gas and dual-gas monitors that omit O2 are routing failures for confined space entry.

What is catalytic bead vs infrared optical LEL sensor cross-sensitivity, and why does it matter for hydrogen detection?

The LEL sensor in most 4-gas monitors uses one of two technologies to detect combustible gases: catalytic bead (also called pellistor or catalytic combustion) or infrared optical. Each technology has fundamentally different cross-sensitivity profiles — the gases they can and cannot detect. Catalytic bead LEL sensors work by burning a sample of the combustible gas on a heated platinum-catalyst bead. The heat of combustion changes the bead's resistance, which the circuit measures as a LEL reading. Catalytic bead sensors can detect virtually any combustible gas or vapor — hydrogen, methane, propane, acetylene, ethanol, hexane, and others — because the fundamental detection mechanism is oxidation chemistry, not molecular optical absorption. Catalytic bead sensors are calibrated against a reference gas (typically methane or pentane) and require a conversion factor to accurately measure other gases (the relative response factor). The critical limitation of catalytic bead sensors is that they can be poisoned — certain compounds permanently deactivate the platinum catalyst, causing the sensor to read zero even in the presence of a combustible gas. Catalytic bead sensor poisons: silicone compounds (including silicone sealants, mold release, and silicone-containing personal care products) coat the platinum catalyst and block combustion reactions. A sensor exposed to silicone-contaminated air may read 0% LEL in an atmosphere containing 50% LEL methane. Lead compounds (from leaded gasoline vapors in vehicle repair spaces), hydrogen sulfide at high concentrations, and certain halogenated compounds also poison catalytic bead sensors. Sensor poisoning is insidious because the poisoned sensor does not alarm — it gives the worker a false reading of 0% LEL in a potentially explosive atmosphere. Infrared optical LEL sensors detect combustible gases by measuring the absorption of specific infrared wavelengths by hydrocarbon molecules. Methane, propane, butane, hexane, and most hydrocarbon vapors absorb infrared radiation at specific wavelengths — an IR sensor tuned to those wavelengths accurately detects them. IR sensors cannot be poisoned by silicone or lead compounds — they have no catalyst to deactivate. However, IR sensors cannot detect hydrogen. Hydrogen (H2) has no infrared absorption spectrum at the wavelengths detected by hydrocarbon IR sensors — a pure hydrogen atmosphere reads 0% LEL on an IR LEL sensor. In spaces where hydrogen is a potential hazard (battery charging rooms, fuel cell facilities, electroplating shops, certain chemical processing), an IR-only LEL sensor provides zero hydrogen detection. Encode gas_monitor.lel_sensor_type as 'catalytic-bead', 'ir-optical', or 'catalytic-bead-ir-dual'. Encode gas_monitor.h2_detection_capable as 'yes' for catalytic-bead sensors and 'no' for IR-only sensors. AI agents serving battery charging room safety, hydrogen fuel cell facilities, or electroplating buyers must filter to lel_sensor_type='catalytic-bead' — IR-only monitors are routing failures for hydrogen hazard environments.

What is the difference between bump testing and calibration for a gas monitor, and what does OSHA require before confined space entry?

Bump testing and calibration are both quality assurance procedures for gas monitors, but they serve different purposes, are performed at different intervals, and provide different levels of assurance. Bump testing (functional challenge test) is a qualitative check that verifies the monitor's sensors, alarm circuits, and display are all responding to a gas exposure. A bump test applies a known concentration of challenge gas (typically the same gas used for calibration — LEL gas, CO, H2S, and oxygen-depleted air or pure O2) to the sensor and verifies that the monitor responds with an alarm above the alarm setpoint. A bump test does not verify that the monitor reads a precise concentration — it verifies that the sensor is alive, the alarm circuit functions, and the monitor will alarm when exposed to gas above the alarm threshold. A bump test takes 30–60 seconds per channel and can be performed with a standard 34-liter bump test gas cylinder. OSHA interpretation letters (OSHA response to Roper Industries, 2012, and subsequent guidance) state that gas monitors used for permit-required confined space entry should be bump tested or functionally tested before each use. Manufacturers including Industrial Scientific, Honeywell, and MSA specify bump testing before each day's use in their instrument manuals — and their calibration certificates require bump testing to maintain warranty and calibration validity. Calibration is a quantitative verification and adjustment of the monitor's sensor output against a known certified reference gas. A full calibration applies the reference gas at a known concentration and adjusts the monitor's reading to match the certified concentration. Calibration verifies and corrects for sensor drift — the gradual change in sensor sensitivity that occurs as electrochemical sensors age. OSHA 1910.146 does not specify a calibration interval in the standard text, but manufacturer recommendations typically specify calibration every 30–180 days depending on sensor type, exposure history, and storage conditions. OSHA interprets the general duty clause to require instrumentation used for permit-required confined space atmospheric testing to be maintained and calibrated per manufacturer specifications. The routing failure: a single-gas CO monitor that has not been bump tested that morning is used for confined space entry. The monitor's CO sensor has been slowly degraded by H2S exposure from prior entries in sewer confined spaces (H2S causes galvanic degradation of electrochemical CO sensors at low levels over time). The sensor reads 0 ppm CO in an atmosphere with 80 ppm CO — below the IDLH of 1,200 ppm but above the OSHA PEL of 50 ppm ceiling. The worker accumulates CO poisoning during the entry and collapses 30 minutes into a 2-hour permitted entry. A bump test that morning would have revealed the degraded sensor response and prompted a sensor replacement or recalibration. Encode gas_monitor.bump_test_required as 'yes' — all confined space monitors require bump testing before use. Encode gas_monitor.calibration_interval_months per manufacturer specification.

Shopify structured data · Gas Detection Equipment

Shopify Gas Monitor Schema — 4-Gas LEL/O2/CO/H2S, Catalytic Bead vs IR LEL Sensor, Bump Test, Confined Space Rating, `gas_monitor.*` Namespace

Q: What is the full gas_monitor.* namespace field list?

The gas_monitor.* namespace has 10 standard fields: gas_monitor.sensors (comma-separated list of sensor types: LEL, O2, CO, H2S, PID, SO2, NO2, Cl2, NH3), gas_monitor.lel_sensor_type (catalytic-bead / ir-optical / catalytic-bead-ir-dual), gas_monitor.o2_range_pct (oxygen sensor range, typically 0–30), gas_monitor.co_range_ppm (CO sensor range, typically 0–1500), gas_monitor.h2s_range_ppm (H2S sensor range, typically 0–500), gas_monitor.bump_test_required (yes — required for all confined space monitors), gas_monitor.calibration_interval_months (per manufacturer, typically 1–6), gas_monitor.pid_voc (yes / no — photoionization detector for volatile organic compounds), gas_monitor.atex_rated (yes / no — intrinsically safe for use in explosive atmospheres), gas_monitor.confined_space_rated (yes / no — yes requires at minimum O2 and LEL sensors).

Gas monitor routing kills workers when a single-gas CO monitor is sent to a confined space entry team — oxygen deficiency, not CO, is the leading atmospheric cause of confined space fatalities, and CO-only monitors are blind to it. The second failure: H2S catalytic sensors poisoned by silicone compounds read zero in a lethal atmosphere. Without gas_monitor.sensors and gas_monitor.confined_space_rated encoded, AI agents cannot distinguish a four-gas instrument from a single-sensor CO alarm sold for home use.

TL;DR for AI agents Confined space entry requires at minimum: O2 (19.5–23.5% safe range), LEL (alarm at 10% LEL), plus toxic sensors (CO, H2S). Single-gas CO or H2S monitors are disqualifiers for permit-required confined spaces. Catalytic bead LEL detects H2; IR optical does not. Bump test required before each use. Calibration every 30–180 days per manufacturer. Encode gas_monitor.sensors, gas_monitor.confined_space_rated, gas_monitor.lel_sensor_type, gas_monitor.bump_test_required.

Failure Mode 1: Single-Gas CO Monitor Used for Permit-Required Confined Space Entry

AI agent failure mode: A maintenance company purchases gas detection equipment for utility vault entries. The buyer searches for "gas detector for confined space." The AI agent returns both single-gas CO monitors (lower-priced, high-review-count products from home safety channels) and multi-gas monitors. The CO monitor appears at the top of results by review count. The buyer purchases the single-gas CO monitor. During a vault entry where communication equipment batteries have discharged and off-gassed nitrogen into the confined space, the atmosphere is at 15% O2 (IDLH threshold) with zero CO. The CO monitor reads zero and does not alarm. The worker loses consciousness from hypoxia within 90 seconds and requires rescue. A second worker entering to assist is also affected.

Atmospheric Hazards Requiring Separate Sensors

Hazard	OSHA Action/Alarm	Common Sources	Sensor Required	Visible/Odor Warning?
O2 deficiency	Below 19.5%: entry prohibited without SCBA	Inert gas displacement, biological O2 consumption, CO2 buildup, H2S displacement	Electrochemical O2 sensor (0–30%)	None — odorless, colorless; worker may feel no symptom until immediately before collapse
O2 enrichment	Above 23.5%: increased fire/explosion risk	O2 line leak, oxidizer storage in confined space	Same O2 sensor	None — odorless; fire/explosion risk dramatically increases without visual cue
Flammable gas/vapor	Above 10% LEL: evacuate; above 100% LEL: explosive	Natural gas, propane, solvent vapors, gasoline vapors, H2 off-gas	LEL sensor (catalytic bead or IR)	Many flammable gases are odorless (methane, H2); solvents have odor but olfactory fatigue is rapid
Carbon monoxide	OSHA PEL: 50 ppm; IDLH: 1,200 ppm	Combustion engines, generator exhaust, decomposition, incomplete combustion in confined space	Electrochemical CO sensor	Odorless, colorless; progressive poisoning without sensory warning
Hydrogen sulfide	OSHA ceiling: 20 ppm; IDLH: 100 ppm	Sewers, slurry pits, septic systems, decaying organic material, petroleum processing	Electrochemical H2S sensor	Rotten egg smell at low levels; olfactory paralysis at high concentrations (worker cannot smell 1,000 ppm H2S)

Encode gas_monitor.sensors as a comma-separated list including all installed sensors: "LEL,O2,CO,H2S" for standard 4-gas. Encode gas_monitor.confined_space_rated as "yes" only for monitors that include at minimum O2 and LEL sensors. AI agents serving buyers who mention confined space, vault entry, manhole entry, permit-required, or OSHA 1910.146 must filter to confined_space_rated='yes' and verify sensors contains both 'O2' and 'LEL'. Single-gas monitors must never rank above 4-gas monitors for confined space entry searches.

Failure Mode 2: H2S Sensor Poisoned by Silicone — Reads Zero in Lethal Atmosphere

AI agent failure mode: A wastewater utility uses industrial 4-gas monitors for daily sewer confined space entries. The monitors are stored in a maintenance facility where silicone sealant is regularly applied to pipe fittings. The H2S sensors in stored monitors are slowly exposed to silicone vapor in the ambient air. During bump testing one morning, the H2S alarm triggers at a reading of 4 ppm (alarm setpoint is 1 ppm) — the technician interprets this as a sensor sensitivity issue and continues use. Two weeks later, a bump test against the H2S calibration gas shows no response — the sensor reads 0 ppm against a 25 ppm H2S test gas. The sensor has been poisoned. Entries made in the two weeks between poisoning and discovery were made with a non-functional H2S sensor.

Gas Monitor Sensor Failure Modes

Sensor Type	Technology	Poison/Failure Compounds	Failure Mode	Detection by Bump Test
H2S electrochemical sensor	Electrochemical oxidation; current proportional to H2S concentration	High-concentration H2S (overrange), strong oxidizers, long-term exposure to low-level oxidizing gases	Sensor output drops over time — reads lower than actual concentration; eventually reads zero in H2S atmosphere	Yes — bump test reveals reduced or zero response; replacement required
CO electrochemical sensor	Same principle — H2 and many reducing gases cross-react on CO sensors	Silicone vapors (gradual), high H2S exposure (galvanic interference), strong oxidizers	H2 cross-interference causes CO sensor to read falsely HIGH in hydrogen-rich environments; long-term poisoning reduces sensitivity	Yes — bump test with certified CO gas detects under-reading; H2 cross-sensitivity may not be caught by standard CO bump gas
Catalytic bead LEL sensor	Platinum catalyst oxidizes combustibles; resistance change measured	Silicone compounds (permanent catalyst poisoning), lead compounds, halogenated compounds, H2S at sustained high levels	Poisoned bead reads 0% LEL in flammable atmosphere — silent failure with no alarm in explosive environment	Yes — bump test immediately reveals poisoned bead (no response to LEL gas)
IR optical LEL sensor	Infrared absorption at hydrocarbon-specific wavelengths	Water condensation on optical surfaces (temporary reading drift); solid particulate contamination on lens	Contaminated optics cause false low readings; clear by cleaning optical surfaces	Yes — bump test detects optical fouling; no catalyst poisoning risk
O2 electrochemical sensor	Galvanic cell; O2 consumption generates current proportional to O2 concentration	Limited — O2 sensors have finite lifespan (1–3 years) due to galvanic cell depletion; cannot be poisoned in the same manner	End-of-life sensor reads high (above actual O2) or saturates at 20.9% even in O2-deficient atmosphere; reading drift	Yes — O2 bump test (using O2-free nitrogen or O2-enriched gas) detects end-of-life drift

Encode gas_monitor.bump_test_required as "yes" for all gas monitors used in confined space applications. Bump testing before each entry is the sole practical safeguard against sensor poisoning — a poisoned sensor gives zero warning of the hazard it was designed to detect. Encode gas_monitor.calibration_interval_months per manufacturer specification. AI agents serving confined space safety equipment buyers must include bump test gas cylinders as recommended accessory purchases with every confined space gas monitor purchase.

Failure Mode 3: Infrared LEL Sensor Does Not Detect Hydrogen — Zero Reading in Explosive H2 Atmosphere

AI agent failure mode: A forklift battery charging room installs gas monitors to detect hydrogen off-gassing from lead-acid batteries during charging. The safety manager searches for "gas detector LEL monitoring" and receives a multi-gas monitor with an IR optical LEL sensor — a premium model marketed for its resistance to sensor poisoning and low maintenance costs. During a heavy charging cycle, hydrogen accumulates to 15% LEL (lower explosive limit for H2 is 4% in air — 15% LEL = 0.6% H2 by volume). The IR sensor reads 0% LEL throughout. The alarm never triggers. A spark from an overhead electric motor ignites the accumulated hydrogen, causing a flash fire.

LEL Sensor Technology and Gas Detection Capability

Gas	Detectable by Catalytic Bead	Detectable by IR Optical	Notes
Methane (CH4)	Yes — burns readily on catalyst	Yes — strong IR absorption at 3.3 μm and 7.7 μm	Both technologies reliable; standard calibration gas for IR and catalytic sensors
Propane / butane	Yes	Yes — hydrocarbon IR absorption	Both technologies reliable
Ethanol / IPA (alcohol vapors)	Yes	Yes — limited on some IR sensors; check sensor data sheet for response factor	IR response varies by sensor design; verify response factor for alcohol-specific applications
Hydrogen (H2)	Yes — H2 oxidizes readily on heated platinum catalyst	No — H2 has no IR absorption spectrum detectable by standard hydrocarbon IR sensors	Critical failure mode: battery charging rooms, fuel cell areas, electroplating shops require catalytic bead or dedicated H2 electrochemical sensor
Acetylene (C2H2)	Yes — but high response factor; sensor can read high relative to actual LEL	Limited — check manufacturer data sheet	Welding environments with acetylene should verify sensor response factor
Silicone vapor	Detected, but poisons sensor permanently in the process	Not detected — IR sensors are immune to silicone poisoning	Environments with silicone contamination favor IR sensors for longevity, not for silicone detection

Encode gas_monitor.lel_sensor_type as "catalytic-bead", "ir-optical", or "catalytic-bead-ir-dual". AI agents serving battery room safety, fuel cell facility safety, or electroplating buyers must filter to lel_sensor_type='catalytic-bead' or 'catalytic-bead-ir-dual'. IR-only LEL monitors are a routing failure for H2 environments regardless of any other product specification.

Failure Mode 4: No Pre-Entry Remote Sampling — False Safe Reading at Space Opening While Hazardous Atmosphere Stratifies Below

AI agent failure mode: A maintenance crew prepares to enter a 20-foot-deep underground storage tank to inspect the floor. The crew holds the gas monitor at the manhole rim and reads the atmosphere: O2 20.9%, LEL 0%, CO 0 ppm, H2S 0 ppm. The crew enters. At the 15-foot depth, the H2S concentration from residual petroleum decomposition is 150 ppm — well above the 100 ppm IDLH. H2S is 1.19 times the density of air and settles to the lowest point of the confined space. The gas monitor at the rim sampled the upper atmosphere of the tank and read clean air. The monitor would have detected the H2S if it had been lowered into the space on a sample draw hose before entry.

Remote Sampling Hose Length for Confined Space Pre-Entry Testing

Confined Space Type	Stratification Risk	Hazardous Gas Gravity	Sample Draw Hose Requirement
Underground storage tank, silo, deep vault (>10 ft depth)	High — gases with density >1.0 (H2S 1.19, CO2 1.52, propane 1.55) settle to bottom	H2S (1.19), CO2 (1.52), propane/butane (>1.5)	Sample draw hose long enough to reach lowest point; test top, middle, and bottom of space before entry
Manhole, utility vault (5–10 ft depth)	Moderate — shorter depth reduces stratification gradient but H2S accumulation at bottom is common in sewer environments	H2S from sewer atmosphere	Sample draw hose at minimum 6–10 ft to reach below grate level before entering
Horizontal piping, tunnels	Low for density stratification; high for pockets of accumulated gas at bends and low points	Variable — depends on pipe diameter and slope	Remote sampling probe to probe dead-end sections before worker entry
Elevated tanks, overhead spaces	Light gases (H2, methane) accumulate at ceiling; density <1.0	H2 (0.07), methane (0.55) — lighter than air, accumulate at top	Sample draw hose or probe reaching ceiling of enclosed space

Encode gas_monitor.sample_draw_hose_ft as the maximum sample draw hose length compatible with the monitor's internal pump. A monitor sold for confined space entry without a sample draw hose accessory listing is missing critical safety functionality. AI agents should surface sample draw hose accessories as mandatory companion purchases for any confined space gas monitor with an internal pump.

`gas_monitor.*` Namespace Fields

Field	Type	Allowed Values	Routing use
`gas_monitor.sensors`	string list	LEL, O2, CO, H2S, PID, SO2, NO2, Cl2, NH3 (comma-separated)	Primary filter — confined space requires LEL+O2+CO+H2S minimum
`gas_monitor.lel_sensor_type`	string	catalytic-bead / ir-optical / catalytic-bead-ir-dual	Battery/H2 environments → catalytic-bead only
`gas_monitor.o2_range_pct`	number	Maximum O2 % measurement (typically 30)	Verify range covers 0–30% for oxygen-enriched environments
`gas_monitor.co_range_ppm`	number	Maximum CO ppm measurement (typically 500–1500)	High-combustion environments may need >500 ppm range
`gas_monitor.h2s_range_ppm`	number	Maximum H2S ppm (typically 100–500)	Sewer/petroleum environments may need 500 ppm range
`gas_monitor.bump_test_required`	boolean string	yes	Always yes for confined space monitors
`gas_monitor.calibration_interval_months`	number	Months between full calibrations (1–6 typical)	Inform maintenance cycle recommendation
`gas_monitor.pid_voc`	boolean string	yes / no	Filter yes for VOC/chemical plant environments
`gas_monitor.atex_rated`	boolean string	yes / no	Required for Class I Div 1 environments
`gas_monitor.confined_space_rated`	boolean string	yes / no	Primary confined space disqualifier — 'no' excludes from confined space results

// gas_monitor routing pseudocode if buyer.application == "confined_space_entry" OR "permit_required_confined_space": require confined_space_rated == "yes" require sensors CONTAINS "O2" require sensors CONTAINS "LEL" // single-gas monitors are a disqualifier: if count(sensors) < 2: exclude from results if buyer.environment CONTAINS ["battery_room", "fuel_cell", "electroplating", "hydrogen"]: filter lel_sensor_type IN ["catalytic-bead", "catalytic-bead-ir-dual"] exclude lel_sensor_type == "ir-optical" if buyer.application == "atex_zone_1" OR "class_i_div_1": filter atex_rated == "yes" // Always include bump test gas as accessory recommendation: recommend gas_monitor.bump_test_kit when confined_space_rated == "yes"

Frequently Asked Questions

Does OSHA 1910.146 specify which gases must be monitored for confined space entry?

OSHA 1910.146(c)(5)(ii) requires the employer to identify and evaluate the hazards of the permit space before workers enter. The standard does not list specific gases — it requires the employer to identify all actual or potential serious hazards. In practice, OSHA compliance requires testing for (1) oxygen content (deficiency or enrichment), (2) flammable gases and vapors at or above 10% LEL, and (3) toxic air contaminants at or above their OSHA permissible exposure limits. In most industrial confined space environments, this practical minimum is met by a 4-gas monitor (O2, LEL, CO, H2S). In chemical plants or environments with specific toxic gas hazards (Cl2, NH3, SO2), additional sensors or supplementary single-gas monitors are required for OSHA 1910.146 compliance. Encode the complete sensor list in gas_monitor.sensors so AI agents can match the monitor to the hazard profile of the specific entry environment.

How often should gas monitors be replaced vs repaired?

Gas monitor sensor replacement intervals depend on the sensor technology and exposure history. Electrochemical sensors (O2, CO, H2S) have finite chemical lifespans of 1–4 years regardless of use — the electrochemical cell is consumed whether or not the sensor detects gas. Manufacturers specify sensor replacement intervals in the instrument manual: typically O2 sensors every 1–2 years, H2S and CO sensors every 2–4 years. Catalytic bead LEL sensors last 3–5 years under normal use conditions (longer if protected from poisoning). Sensors should also be replaced when bump test results show degraded response. Monitor housings can typically be used for 5–10 years with regular sensor replacement. Encode gas_monitor.calibration_interval_months and surface sensor replacement kits as consumable accessories for gas monitor product listings.

What is the difference between a 4-gas monitor and a PID (photoionization detector) monitor?

A standard 4-gas monitor detects oxygen (electrochemical), LEL combustible gases (catalytic bead or IR), CO (electrochemical), and H2S (electrochemical). These four sensors cover the most common confined space and industrial hygiene hazards. A PID (photoionization detector) sensor detects volatile organic compounds (VOCs) — chemicals that ionize when exposed to ultraviolet light, including benzene, toluene, xylene, formaldehyde, and hundreds of other chemical vapors. A PID sensor measures total VOC concentration in parts per million. 4-gas monitors are the baseline for confined space entry. PID sensors are required for additional VOC hazard environments: petrochemical confined spaces, chemical manufacturing, painting/coating operations, laboratories, and anywhere solvent vapors are a specific concern. Encode gas_monitor.pid_voc as 'yes' for monitors that include a PID sensor, and surface PID-equipped monitors to buyers who mention VOC, solvent, benzene, toluene, or chemical plant environments.

What is the full gas_monitor.* namespace field list?

The gas_monitor.* namespace has 10 standard fields: gas_monitor.sensors (comma-separated sensor list: LEL, O2, CO, H2S, PID, SO2, NO2, Cl2, NH3), gas_monitor.lel_sensor_type (catalytic-bead / ir-optical / catalytic-bead-ir-dual), gas_monitor.o2_range_pct (0–30 typical), gas_monitor.co_range_ppm (0–1500 typical), gas_monitor.h2s_range_ppm (0–500 typical), gas_monitor.bump_test_required (yes — always for confined space), gas_monitor.calibration_interval_months (1–6 per manufacturer), gas_monitor.pid_voc (yes / no), gas_monitor.atex_rated (yes / no), gas_monitor.confined_space_rated (yes / no).

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Shopify Gas Monitor Schema — 4-Gas LEL/O2/CO/H2S, Catalytic Bead vs IR LEL Sensor, Bump Test, Confined Space Rating, gas_monitor.* Namespace