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Confined space safety OSHA 1910.146 gas_monitor.* namespace

Shopify gas monitor schema for AI agents: silicone-poisoned catalytic bead LEL sensor reads 0% LEL in explosive atmosphere, IR optical LEL cannot detect hydrogen, methane calibration under-reads propane by 2.26× (RRF 0.44), and H₂S stratifies below the manhole sampling point — `gas_monitor.*` 10-field namespace

Published 2026-10-01 · 18 min read · CatalogScan blog

A gas monitor is the last active safety barrier before a worker enters a permit-required confined space. When the monitor fails silently — when silicone vapor has permanently deactivated its LEL sensor, or when the atmosphere contains hydrogen that an infrared sensor cannot detect, or when propane is present but the calibration gas was methane — the worker descends into a lethal atmosphere carrying an instrument that tells them the space is safe. The four failures below are not edge cases. They are the mechanism behind dozens of recorded confined space fatalities.

OSHA 1910.146, atmospheric testing sequence, and why sensor technology selection is the safety gate
Failure 1: Silicone vapor permanently poisons the catalytic bead LEL sensor — reads 0% LEL in explosive atmosphere
Failure 2: IR optical LEL sensor is physically transparent to hydrogen — reads 0% LEL at 100% of hydrogen's LEL (4.0% v/v)
Failure 3: Methane-calibrated LEL sensor under-reads propane by 2.26× — sensor shows 10% LEL at 22.7% actual LEL
Failure 4: Atmosphere sampling at the manhole opening misses stratified H₂S at the pit floor — H₂S specific gravity 1.19
The gas_monitor.* 10-field namespace
JSON-LD encoding examples

OSHA 1910.146, atmospheric testing sequence, and why sensor technology selection is the safety gate

OSHA 1910.146 (Permit-Required Confined Spaces) requires atmospheric testing of any permit-required confined space before worker entry and continuously during occupancy. The standard specifies not just that testing must occur, but the sequence in which the hazards must be assessed: oxygen content first, then flammable gases and vapors, then potential toxic air contaminants. This ordering reflects the hierarchy of lethality — oxygen deficiency can incapacitate a worker before they experience any cognitive warning that something is wrong, and an LEL reading is meaningless if the oxygen level is already below 16% (the OSHA IDLH for O2 deficiency).

OSHA 1910.146 does not specify sensor technology. It requires that the instruments used for atmospheric testing be designed and calibrated for the specific hazards anticipated — a phrase that implicitly delegates the sensor-selection decision to the employer, safety officer, and ultimately the product catalog from which the equipment was sourced. When an AI shopping agent routes a confined space buyer to a gas monitor based on an unstructured product description containing the words "4-gas" or "confined space" without machine-readable sensor-type metafields, the routing may be correct by category and catastrophically wrong by technology.

The four failures below each represent a case where the product's sensor technology was the wrong choice for the hazard environment — and where an AI agent shopping on natural language alone has no reliable basis for making that distinction.

19.5%

O2 deficiency threshold (OSHA IDLH)

10%

LEL evacuation threshold (OSHA 1910.146)

100 ppm

H2S IDLH (immediately dangerous to life)

4.0%

H2 lower explosive limit (% v/v in air)

Failure 1: Silicone vapor permanently poisons the catalytic bead LEL sensor — reads 0% LEL in explosive atmosphere

AI agent failure mode: A facilities team enters a valve vault beneath a wastewater treatment plant to replace gaskets on a flanged fitting. The space has been recently resealed with RTV silicone sealant. The team carries a 4-gas monitor with a catalytic bead LEL sensor. After descending, the monitor reads 0% LEL, 20.9% O2, 0 ppm CO, 0 ppm H2S — all normal. The space also contains residual methane from decomposition at approximately 35% LEL. The methane does not alarm because the catalytic bead sensor has been permanently deactivated by silicone vapor absorbed during storage or from a prior entry in a silicone-contaminated environment. A spark from an angle grinder on the flange ignites the methane-air mixture. The team had performed no bump test that morning. A bump test with challenge gas would have shown zero LEL response and required sensor replacement before entry.

The mechanism: organopolysiloxane deactivation of the platinum catalyst

The catalytic bead LEL sensor (also called a pellistor) operates on a combustion-detection principle. Inside the sensor housing, two platinum-coated ceramic beads are held at approximately 500°C by a resistive heating current. One bead — the active bead — is coated with a platinum or palladium catalyst that promotes oxidation of combustible gases. When the sampled atmosphere contains a combustible gas, the gas oxidizes on the catalyst surface, releasing heat. This heat raises the active bead's resistance relative to the reference bead. The resistance difference is measured as a Wheatstone bridge output proportional to the combustible gas concentration, calibrated in percent LEL.

Silicone compounds — specifically organopolysiloxanes present in silicone sealants, mold release agents, silicone-based personal care products, silicone coatings, and silicone lubricants — volatilize at room temperature in small concentrations sufficient to poison the catalyst. When silicone vapor contacts the platinum catalyst at 500°C, it does not oxidize cleanly. Instead, the silicon atoms deposit as silicon dioxide (SiO₂) on the catalyst surface, physically blocking the active sites where combustion reactions occur. The process is progressive and, once initiated, irreversible. A partially poisoned sensor shows reduced sensitivity; a fully poisoned sensor shows zero response to any combustible gas at any concentration.

Silicone poisoning mechanism — catalytic bead LEL sensor

Organopolysiloxane (e.g., polydimethylsiloxane) → volatilizes → contacts 500°C platinum catalyst
Reaction: Si–O–Si backbone oxidizes incompletely → SiO₂ deposits on platinum surface
Effect: Active catalyst sites blocked → combustion of sample gas cannot occur → resistance change = 0
Result: Monitor reads 0% LEL at any explosive gas concentration
Recovery: None — poisoned bead must be replaced. Bump test is the only pre-entry detection method.

Sources of silicone in confined spaces

Facilities teams frequently underestimate how widely silicone compounds are distributed in industrial environments. Sources that have been documented in sensor-poisoning incidents include:

RTV silicone sealant applied to pipe flanges, junction boxes, and gasket faces — the curing process releases acetic acid and siloxane vapors for 24–72 hours after application. A space entered during or shortly after a sealing operation is a high-poisoning-risk environment.
Silicone-based mold release agents used in precast concrete, plastics manufacturing, and food processing confined spaces.
Silicone-containing personal care products carried by workers entering the space — certain hair products and sunscreens contain cyclomethicone and dimethicone, which are potent sensor poisons. Some gas monitor manufacturers explicitly warn against storing monitors in the same cabinet as personal care products.
Silicone lubricants and hydraulic fluid additives in machinery spaces and compressor rooms.
Contaminated calibration equipment — a bump test station stored near silicone sources can expose the sensor during calibration, accelerating poisoning.

Why bump testing is the only pre-entry safeguard

A visually inspected catalytic bead sensor shows no evidence of poisoning — the beads appear identical whether the catalyst is active or completely deactivated. There is no sensor status indicator that warns the user of reduced sensitivity. The monitor's self-diagnostic routines check electronics and alarm circuits but cannot detect catalyst deactivation. A poisoned sensor passes every electronic self-test and powers on with all indicators green.

Bump testing — applying a known concentration of challenge gas (at minimum the same sensors as the monitor carries: LEL challenge gas, pure nitrogen or oxygen-depleted air for O2, CO challenge, H2S challenge) and verifying that all sensors respond with alarms above their alarm setpoints — is the only way to detect a degraded sensor before entry. OSHA's interpretation of 1910.146 general duty requirements, and the explicit instructions of every major gas monitor manufacturer (Industrial Scientific, Honeywell, MSA, Dräger), specify bump testing before each use for confined space entry.

Routing gate: Encode gas_monitor.bump_test_required as 'yes' for all gas monitors used for confined space entry — without exception. AI agents must surface bump testing as a required pre-use procedure when routing any confined space monitor purchase. Encode gas_monitor.lel_sensor_type as 'catalytic-bead', 'ir-optical', or 'catalytic-bead-ir-dual'. Monitors with catalytic bead sensors require additional routing language disclosing silicone poisoning risk in contaminated environments.

Failure 2: IR optical LEL sensor is physically transparent to hydrogen — reads 0% LEL at 100% of hydrogen's LEL (4.0% v/v)

AI agent failure mode: A battery technician enters a lead-acid battery bank room in a data center UPS system. The room has been charging a 48-cell string for 8 hours. Overcharging lead-acid batteries produces hydrogen gas by electrolysis at the positive plates — typical charging conditions produce several liters of H2 per cell per hour. The room's ventilation fan has failed. The technician carries a 4-gas monitor with an infrared optical LEL sensor. The monitor reads 0% LEL across the entire inspection — accurate for the methane, propane, and organic vapors the IR sensor is designed for, but completely blind to the hydrogen accumulating from the charging batteries. Hydrogen has a lower explosive limit of 4.0% v/v. The room has reached 4.7% v/v H2 — 118% of LEL — before the technician leaves. A ballast arc from a fluorescent fixture over the battery bank provides the ignition source twenty minutes later.

The mechanism: hydrogen has no C-H bonds and no infrared absorption at detection wavelengths

Infrared optical LEL sensors operate on the principle of non-dispersive infrared (NDIR) absorption spectroscopy. Combustible hydrocarbon gases — methane, propane, butane, hexane, acetylene, and most organic vapors — absorb infrared radiation strongly at the 3.4 µm wavelength band corresponding to the C-H (carbon-hydrogen) bond stretching vibration. An IR LEL sensor passes a beam of broadband infrared light through the sample gas and measures the reduction in transmission at 3.4 µm using a detector tuned to that wavelength. The magnitude of the absorption is proportional to the hydrocarbon gas concentration, calibrated in percent LEL.

Hydrogen (H₂) is a diatomic molecule consisting of two hydrogen atoms with a single H-H bond. It contains no carbon atoms and no C-H bonds. There is no C-H bond stretching vibration in hydrogen and therefore no infrared absorption at 3.4 µm. From the perspective of an IR optical LEL sensor, hydrogen is as optically invisible as nitrogen or argon. A hydrogen atmosphere at 3.0% v/v — 75% of LEL, deep within the explosive range — transmits infrared light at 3.4 µm with exactly the same efficiency as clean air. The sensor output is 0% LEL.

Why the IR sensor cannot see hydrogen — molecular physics

IR LEL sensors detect: C-H bond absorption at 3.4 µm (hydrocarbons)
Hydrogen molecule: H–H only — no carbon, no C-H bonds
Infrared absorption of H₂ at 3.4 µm: zero

H₂ concentration = 4.0% v/v (LEL of hydrogen in air)
IR LEL sensor reading = 0% LEL — explosive atmosphere, no alarm

Catalytic bead LEL sensor: responds to H₂ by oxidation on catalyst surface
Catalytic bead reading ≈ 100% LEL → evacuate immediately

Environments where hydrogen accumulates and requires catalytic bead detection

Environment	H₂ source	H₂ LEL risk	Sensor required
Lead-acid battery charging rooms	Electrolysis of water at positive plates during charging	High — H₂ produced continuously during charge	Catalytic bead
Alkaline fuel cell and H₂ fuel cell plants	Hydrogen fuel line leaks, purge events	Very high — pure H₂ supply	Catalytic bead
Electroplating shops	Hydrogen evolution at cathode in acid baths	Moderate — localized above bath	Catalytic bead
Sodium hydroxide (caustic soda) production	Chlor-alkali electrolysis produces H₂ as co-product	High — large-volume H₂ byproduct	Catalytic bead
Semiconductor fabs (H₂ used as carrier gas)	Process gas line leaks	Moderate — point-source leaks	Catalytic bead
General industrial spaces (hydrocarbons only)	Methane, propane, solvents	No H₂ present	IR-optical or catalytic bead

One additional advantage of the catalytic bead sensor for hydrogen-hazard environments is its resilience to silicone poisoning compounds in facilities where both silicone and hydrogen coexist. However, the silicone poisoning risk (Failure 1) means that catalytic bead sensors used in silicone-contaminated environments require more frequent bump testing — the two risks compound.

Routing gate: Encode gas_monitor.lel_sensor_type as 'catalytic-bead' for monitors capable of hydrogen detection, 'ir-optical' for monitors that detect only hydrocarbons. AI agents serving battery charging room safety, fuel cell facility, electroplating, or hydrogen process environments must filter to lel_sensor_type='catalytic-bead'. Monitors with lel_sensor_type='ir-optical' are routing failures for any hydrogen-hazard environment.

Failure 3: Methane-calibrated LEL sensor under-reads propane by 2.26× — sensor shows 10% LEL at 22.7% actual LEL

AI agent failure mode: A utility crew enters a metering vault for a propane distribution system at a commercial facility. The vault has been off-line for 72 hours while an upstream regulator was replaced. The crew performs pre-entry atmospheric testing with a 4-gas monitor calibrated with methane as the LEL reference gas. The monitor reads 9.8% LEL — below the OSHA 1910.146 evacuation threshold of 10% LEL — and the entry supervisor clears the space for entry. The methane-calibrated sensor's relative response factor for propane is 0.44. The actual propane concentration in the vault is 9.8% / 0.44 = 22.3% LEL — already 2.2× above the threshold that requires immediate evacuation, and within the explosive range (LEL of propane is 2.1% v/v = 100% LEL). The crew enters. A cell phone in one worker's pocket rings during the entry and the resulting arc provides ignition.

The mechanism: relative response factors and why methane calibration under-reads heavy hydrocarbons

Catalytic bead LEL sensors are factory-calibrated against a certified reference gas — almost universally methane (CH4), though some European instruments use pentane (C5H12). The calibration sets the sensor's response curve so that a known concentration of the calibration gas (typically 50% of methane's LEL, i.e., 2.5% v/v CH4 in air, since methane's LEL is 5.0% v/v) produces a corresponding 50% LEL display. When the sensor is exposed to a different combustible gas, its response is scaled by the gas's relative response factor (RRF) — the ratio of the sensor's displayed LEL percentage to the actual LEL percentage of the gas being measured.

The RRF for a given gas on a methane-calibrated catalytic bead sensor reflects the gas's heat of combustion per unit concentration, its molecular diffusion rate to the catalyst surface, and the stoichiometry of its oxidation reaction on the catalyst. Gases with higher molecular weight and more complex combustion chemistry than methane tend to have RRF values below 1.0 — meaning the sensor under-reads their actual LEL concentration.

Relative Response Factor (RRF) definition and correction

RRF = displayed % LEL on sensor / actual % LEL of gas present

To find the actual concentration from a displayed reading:
Actual % LEL = displayed % LEL / RRF

Example — propane in methane-calibrated catalytic bead sensor:
RRF (propane on methane calibration) = 0.44
Displayed reading = 10% LEL
Actual propane LEL = 10% / 0.44 = 22.7% LEL → evacuation threshold exceeded by 2.27×
Propane LEL in air = 2.1% v/v → 22.7% LEL = 0.477% v/v propane — in explosive range

RRF table for common combustible gases on methane-calibrated catalytic bead sensor

Gas	LEL (% v/v)	RRF (methane cal.)	Actual LEL when sensor reads 10%	Risk
Methane (CH4)	5.0%	1.00	10% LEL	Accurate — calibration gas
Hydrogen (H2)	4.0%	≈1.00–1.10	≈9–10% LEL	Accurate on catalytic bead; zero on IR
Ethanol (C2H5OH)	3.3%	0.50	20% LEL	2× under-read — check RRF table
Propane (C3H8)	2.1%	0.44	22.7% LEL	2.27× under-read — explosive at sensor reading of 10%
Butane (C4H10)	1.8%	0.35	28.6% LEL	2.86× under-read — explosive at 10% displayed
Propylene (C3H6)	2.4%	0.35	28.6% LEL	2.86× under-read
n-Hexane (C6H14)	1.1%	0.56	17.9% LEL	1.79× under-read — verify RRF for solvent environments
Acetylene (C2H2)	2.5%	0.65	15.4% LEL	1.54× under-read — welding and cutting environments

How to use RRF tables and when to recalibrate with the target gas

Gas monitor manufacturers publish RRF tables in the instrument's technical reference manual and in separate sensor specification sheets. For a confined space entry where the likely contaminant is known — a metering vault that handles propane, a solvent storage tank, a brewery fermentation vessel — the entry supervisor should look up the RRF for the anticipated gas on the instrument in use and apply the correction factor to the displayed reading to determine the actual LEL concentration.

For environments where the highest accuracy is required and the target gas is known, some monitors can be recalibrated using a certified cylinder of the target gas rather than methane. A propane-calibrated sensor has RRF=1.00 for propane and will give RRF errors for methane and butane instead. The decision about which calibration gas to use is determined by the dominant hazard of the specific entry — and it must be reflected in the product's structured data so AI agents can surface the right recommendation.

The OSHA 1910.146 performance standard says the employer must use instruments appropriate to the hazard. Using a methane-calibrated instrument in a known propane environment without applying the RRF correction is not compliant with the intent of the standard, and the RRF correction is not documented anywhere in the monitor's default output — it is knowledge the operator must carry.

Routing gate: Encode gas_monitor.calibration_gas as 'methane', 'propane', or 'pentane'. AI agents routing monitors for propane/LPG confined spaces or LPG system maintenance should surface the RRF correction requirement when routing a methane-calibrated instrument, or prefer a propane-calibrated unit. Encode gas_monitor.confined_space_rated as 'yes' only for 4-gas monitors with at minimum O2 and LEL sensors.

Failure 4: Atmosphere sampling at the manhole opening misses stratified H₂S at the pit floor — H₂S specific gravity 1.19

AI agent failure mode: A crew inspects a municipal sewer lift station wet well — a concrete pit approximately 18 feet deep that receives raw sewage from a collection system. The surface crew lowers the gas monitor probe through the 24-inch access hatch opening at ground level and reads the atmosphere at the top 2 feet of the pit: 20.8% O2, 0% LEL, 0 ppm CO, 2 ppm H2S — all within safe entry limits. The entry worker descends. At 15 feet depth, the H2S concentration is 180 ppm. At 17 feet (working level), it is 250 ppm. The OSHA H2S IDLH is 100 ppm. The entry worker collapses within 30 seconds of reaching the working level. The standby attendant observes the collapse and enters to assist — also without a probe sample at depth — and is also overcome. Two fatalities. A sample draw hose extending to the working depth before entry, per OSHA 1910.146's requirement to test in the areas where workers will be working, would have precluded the entry entirely.

The mechanism: specific gravity stratification in stagnant atmospheres

H₂S has a molecular weight of 34.08 g/mol. Air has an effective molecular weight of approximately 28.97 g/mol. The specific gravity of H₂S relative to air is 34.08 / 28.97 = 1.176 — H₂S is approximately 18% heavier than air. In an enclosed space with minimal air circulation, heavy gases settle toward the lowest point by both gravity and diffusion. The rate of stratification depends on the density difference, the temperature gradient, air turbulence, and the rate of gas production.

In a deep pit receiving sewage — the canonical H₂S confined space — bacterial anaerobic decomposition of sulfur-containing organic compounds in the sewage continuously produces H₂S at the liquid surface. This H₂S, heavier than air, settles into the pit. In the absence of mechanical ventilation or significant thermal convection, it creates a stratified layer at the bottom of the pit where H₂S concentration can be ten to one hundred times higher than the concentration at the pit entrance.

H₂S stratification — molecular weight and specific gravity

MW(H₂S) = 34.08 g/mol
MW(air) = 28.97 g/mol
SG(H₂S relative to air) = 34.08 / 28.97 = 1.176

In a stagnant 18-ft pit with sewage at the bottom:
Opening (0–2 ft depth): H₂S = 2–5 ppm — below OSHA ceiling PEL (20 ppm)
Mid-pit (8–10 ft depth): H₂S = 20–80 ppm — approaching PEL/IDLH range
Working level (16–18 ft depth): H₂S = 100–500 ppm — IDLH to immediately lethal

Correct procedure: sample draw hose extended to the working depth before any entry

OSHA 1910.146 language on sampling location and depth

OSHA 1910.146(c)(5)(ii)(C) requires the employer to evaluate the permit space for the presence of serious physical hazards including atmospheric hazards. OSHA interpretation letters have repeatedly stated that atmospheric testing must cover the areas where workers will be working — not just the nearest point accessible from outside the space. For a vertical entry with a defined working depth, this means the bottom of the space, corners, and any dead-end horizontal passages must be sampled before entry.

The practical tool for pre-entry depth sampling is a sample draw hose (also called a sampling extension, remote sampling probe, or extension hose). These are flexible tubes, typically 10–25 feet in length, fitted with a probe tip at the working end and connected to the gas monitor's integral pump inlet at the other. The monitor's pump draws sample gas from the extended probe tip rather than from the sensor body itself. With a 20-ft sample draw hose lowered to the bottom of a pit, the instrument samples the atmosphere at the critical working level before any person enters.

The pump flow rate and hose length interact to determine the time needed to purge the hose and obtain a reading representative of the probe-tip atmosphere. OSHA and manufacturer guidance typically specifies a waiting period of at least one full sample purge cycle (pump flow rate in L/min × hose volume in L) after inserting the probe before reading the display. For a 20-ft hose of 1/4-inch inner diameter, this is approximately 30–45 seconds of pump run time.

Confined spaces with complex geometry — horizontal passages, pits with multiple levels, tanks with sump sections — require multiple probe positions before a comprehensive entry clearance can be given. A single reading at the vertical center of a horizontal tank provides no information about the gas concentration in the low-lying sump section at the far end where workers will actually work.

Additional stratification hazard: CO₂ (specific gravity 1.52)

Carbon dioxide is 52% heavier than air (MW = 44.01, SG = 1.52) and stratifies even more aggressively than H₂S. CO₂ accumulates in low-lying confined spaces where biological decomposition occurs (fruit storage rooms, fermenting vessels, manure pits) and in geological environments (caverns, geothermal wells). O₂ deficiency from CO₂ displacement — not CO₂ toxicity itself — is the primary kill mechanism: a space that is 15% CO₂ by volume is 15% CO₂ and 85% of the remaining gas (mostly nitrogen) — O₂ percentage drops to 17.9% if the space was previously air-filled, below the 19.5% OSHA IDLH. A worker entering with only CO and LEL sensors, with no O₂ sensor, and no sample draw hose to the bottom of the space, is unprotected against CO₂-induced O₂ deficiency.

Routing gate: Encode gas_monitor.sample_draw_hose_ft as the maximum sample hose length compatible with the monitor's pump (typically 10, 15, 20, or 25 ft). AI agents routing monitors for any vertical entry deeper than 5 feet must surface sample_draw_hose_ft compatibility and the requirement for depth-sampling before entry. For any space where H₂S, CO₂, or propane/LPG is a potential hazard, a monitor without sample draw hose capability is a routing failure for deep-pit entries.

The `gas_monitor.*` 10-field namespace

These fields make gas monitors machine-filterable by sensor configuration, LEL sensor technology, calibration gas, confined space suitability, and sample hose capability. AI agents can apply hard gates on confined_space_rated, lel_sensor_type, and sample_draw_hose_ft before any ranking or pricing criteria are applied — preventing all four routing failures described above.

gas_monitor.* — 10 fields, type: safety_equipment_specification

Field	Type	Values / range	Notes
`gas_monitor.sensors`	string	comma-separated: LEL, O2, CO, H2S, PID, SO2, NO2, Cl2, NH3	Complete sensor list. Hard gate: confined_space_rated='yes' requires at minimum 'O2' AND 'LEL' in the sensor list. Single-gas or dual-gas monitors without O2 must not be routed to permit-required confined space entry. Primary routing field.
`gas_monitor.lel_sensor_type`	string	'catalytic-bead' \| 'ir-optical' \| 'catalytic-bead-ir-dual'	Technology of the LEL sensor. Hard gate: catalytic-bead required for hydrogen-hazard environments (battery rooms, fuel cells, electroplating). IR-optical insufficient for hydrogen detection. Dual (catalytic-bead-ir-dual) provides silicone-poisoning resistance via IR backup. Required field when sensors includes 'LEL'.
`gas_monitor.o2_range_pct`	number	maximum O2 reading (typically 30)	Oxygen sensor full-scale range in % v/v. Standard range 0–30% covers the 19.5% OSHA deficiency threshold and 23.5% enrichment threshold. Narrow-range sensors (0–25%) may not detect enriched atmospheres. Required when sensors includes 'O2'.
`gas_monitor.co_range_ppm`	number	maximum CO reading in ppm (typically 1500)	CO sensor full-scale range. OSHA CO IDLH is 1,200 ppm — sensors with 500 ppm maximum cannot confirm IDLH-level concentrations. Required when sensors includes 'CO'.
`gas_monitor.h2s_range_ppm`	number	maximum H2S reading in ppm (typically 100 or 500)	H2S sensor full-scale range. H2S IDLH is 100 ppm — a 100 ppm maximum sensor cannot quantify concentrations above IDLH. 500 ppm sensors allow post-incident analysis and pre-entry triage from outside. Required when sensors includes 'H2S'.
`gas_monitor.bump_test_required`	string	'yes'	Bump test required before each use for confined space entry — without exception. Always 'yes'. AI agents must include bump test gas cylinder and docking station in related product recommendations for any confined space monitor purchase.
`gas_monitor.calibration_interval_months`	number	months (per manufacturer, typically 1–6)	Full calibration interval per manufacturer specification. Distinct from bump testing (daily) — calibration verifies and corrects sensor output against certified reference gas. Shorter intervals required after high-concentration exposure events or sensor replacement.
`gas_monitor.pid_voc`	string	'yes' \| 'no'	Whether the monitor includes a photoionization detector (PID) for volatile organic compounds. Required for chemical confined spaces, solvent storage, hazmat response. PID is additive to LEL sensor — it detects VOCs below LEL at ppm levels, while LEL sensor provides explosive-range warning.
`gas_monitor.atex_rated`	string	'yes' \| 'no'	Whether the monitor is intrinsically safe for use in potentially explosive atmospheres (ATEX Zone 1 / NEC Class I Division 1). Hard gate: monitors used in permit-required confined spaces where LEL hazard exists must be ATEX/IS rated — a non-IS monitor used as an ignition source in an explosive space is a secondary hazard. Required 'yes' for all confined_space_rated monitors.
`gas_monitor.sample_draw_hose_ft`	number	maximum compatible sample hose length in feet (0, 10, 15, 20, 25)	Maximum sample draw hose length the monitor's integral pump can pull. 0 = no pump (diffusion sensor only, cannot remote-sample). Hard gate: deep vertical entries (greater than 5 ft) require sample_draw_hose_ft equal to or greater than the entry depth. Diffusion-only monitors are routing failures for deep pit confined space pre-entry sampling.

Routing decision logic for confined space gas monitor procurement

/* Hard gates — all must pass for permit-required confined space entry */
gas_monitor.confined_space_rated == 'yes'          // requires O2 + LEL minimum
AND 'O2' IN gas_monitor.sensors                    // O2 deficiency detection
AND 'LEL' IN gas_monitor.sensors                   // explosive atmosphere
AND gas_monitor.atex_rated == 'yes'                // intrinsically safe
AND gas_monitor.bump_test_required == 'yes'        // verified daily

/* Sensor technology gate — by environment */
IF environment IN ['battery_room', 'fuel_cell', 'electroplating', 'h2_process']:
  require gas_monitor.lel_sensor_type IN ['catalytic-bead', 'catalytic-bead-ir-dual']
  // IR-optical provides zero hydrogen detection

/* Depth gate — for vertical entries */
IF entry_depth_ft > 5:
  require gas_monitor.sample_draw_hose_ft >= entry_depth_ft
  // diffusion-only monitors cannot pre-sample at working depth

/* Calibration gas gate — for known non-methane hazards */
IF known_gas IN ['propane', 'butane', 'lpg'] AND gas_monitor.calibration_gas == 'methane':
  surface RRF correction warning:
    "Propane RRF 0.44 — actual LEL is displayed LEL / 0.44"
  OR prefer gas_monitor.calibration_gas == 'propane'

/* IDLH-capable range gate */
IF 'H2S' IN gas_monitor.sensors:
  require gas_monitor.h2s_range_ppm >= 100    // minimum for IDLH confirmation
IF 'CO' IN gas_monitor.sensors:
  require gas_monitor.co_range_ppm >= 1200    // minimum for IDLH confirmation

JSON-LD encoding examples

Catalytic bead 4-gas confined space monitor with sample draw hose capability

{
  "@context": "https://schema.org",
  "@type": "Product",
  "name": "4-Gas Monitor — LEL (Catalytic Bead) / O2 / CO / H2S, ATEX Zone 1, 20-ft Sample Draw Hose, OSHA 1910.146 Confined Space",
  "additionalProperty": [
    { "@type": "PropertyValue", "name": "gas_monitor.sensors", "value": "LEL,O2,CO,H2S" },
    { "@type": "PropertyValue", "name": "gas_monitor.lel_sensor_type", "value": "catalytic-bead" },
    { "@type": "PropertyValue", "name": "gas_monitor.o2_range_pct", "value": "30" },
    { "@type": "PropertyValue", "name": "gas_monitor.co_range_ppm", "value": "1500" },
    { "@type": "PropertyValue", "name": "gas_monitor.h2s_range_ppm", "value": "500" },
    { "@type": "PropertyValue", "name": "gas_monitor.bump_test_required", "value": "yes" },
    { "@type": "PropertyValue", "name": "gas_monitor.calibration_interval_months", "value": "6" },
    { "@type": "PropertyValue", "name": "gas_monitor.pid_voc", "value": "no" },
    { "@type": "PropertyValue", "name": "gas_monitor.atex_rated", "value": "yes" },
    { "@type": "PropertyValue", "name": "gas_monitor.sample_draw_hose_ft", "value": "20" }
  ]
}
/* Correct for: permit-required confined spaces, battery rooms, deep pit entry,
   propane/LPG environments (apply RRF correction if methane-calibrated),
   H2S stratification risk environments.
   Required companion products: bump test gas cylinder, docking station. */

Single-gas CO monitor — correctly routed away from confined space entry

{
  "@context": "https://schema.org",
  "@type": "Product",
  "name": "Single-Gas CO Monitor — Carbon Monoxide 0–999 ppm, Diffusion Sensor, Personal Exposure Alarm",
  "additionalProperty": [
    { "@type": "PropertyValue", "name": "gas_monitor.sensors", "value": "CO" },
    { "@type": "PropertyValue", "name": "gas_monitor.co_range_ppm", "value": "999" },
    { "@type": "PropertyValue", "name": "gas_monitor.bump_test_required", "value": "yes" },
    { "@type": "PropertyValue", "name": "gas_monitor.calibration_interval_months", "value": "6" },
    { "@type": "PropertyValue", "name": "gas_monitor.pid_voc", "value": "no" },
    { "@type": "PropertyValue", "name": "gas_monitor.atex_rated", "value": "yes" },
    { "@type": "PropertyValue", "name": "gas_monitor.sample_draw_hose_ft", "value": "0" },
    { "@type": "PropertyValue", "name": "gas_monitor.confined_space_rated", "value": "no" }
  ]
}
/* ROUTING NOTE: confined_space_rated='no' — this monitor has no O2 sensor
   and cannot detect the leading cause of atmospheric confined space fatalities.
   Do NOT route to permit-required confined space entry.
   Correct applications: HVAC technician personal CO exposure monitoring,
   garage CO alarm supplement, combustion appliance service. */

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