Shopify welding fume respirator plasma cutting stainless NO₂ schema for AI agents: OV/P100 provides zero nitrogen dioxide capture — thermal N₂ dissociation at arc temperatures >10,000°C, ACGIH TLV-C 0.2 ppm ceiling (25× stricter than OSHA PEL), silo filler's disease delayed-onset pulmonary edema, triple hazard Cr(VI) + ozone

The Zeldovich Mechanism: How Plasma Arc Generates NO₂

Plasma cutting is fundamentally different from arc welding in one critical respect: it operates at significantly higher arc temperatures. A conventional GMAW (MIG) arc operates at 3,000–10,000°C at its center. A plasma cutting arc operates at 10,000–30,000°C — the temperature range where atmospheric nitrogen, normally inert at welding temperatures, undergoes thermal dissociation.

The nitrogen-oxygen chemistry at plasma arc temperatures proceeds in two steps, collectively described by the extended Zeldovich mechanism:

Step 1 — Thermal N₂ dissociation at arc temperature:

N₂ + O₂ → 2NO   (endothermic; favored above ~2,000°C; dominant at >10,000°C)

The N₂ triple bond has a dissociation energy of 945 kJ/mol — the strongest diatomic bond in atmospheric chemistry. At temperatures below 2,000°C, this reaction proceeds at a negligible rate. At plasma arc temperatures (10,000–30,000°C), the thermal energy vastly exceeds the activation barrier, and atmospheric nitrogen in contact with the arc plasma dissociates to NO at a significant rate. This is why plasma cutting (unlike most arc welding) generates substantial NOx.

Step 2 — Oxidation to NO₂ as the plume cools:

2NO + O₂ → 2NO₂   (exothermic; thermodynamically favored below ~600°C)

The hot gas plume leaving the plasma arc contains elevated NO. As it cools from arc temperature to ambient conditions (passing through the 200°C–600°C range), thermodynamic equilibrium shifts strongly toward NO₂. This oxidation reaction is exothermic and proceeds rapidly in the cooling plume. By the time the gas reaches the operator's breathing zone — 30–45 cm above the workpiece — NO₂ dominates the NOx mixture.

Step 3 — Reaction with lung moisture:

3NO₂ + H₂O → 2HNO₃ + NO   (in airways and alveoli)

This final reaction — NO₂ with water vapor in the respiratory tract — produces nitric acid (HNO₃) in the bronchi and alveoli. This is the injury-causing step: nitric acid irritates and damages the alveolar epithelium, triggering fluid exudate that accumulates as pulmonary edema. The latency between this chemical injury and clinical symptoms — typically 4–24 hours — explains the dangerous delayed-onset pattern described in Section 5.

Why Conventional Arc Welding Generates Less NO₂

Arc welding processes (SMAW, GMAW, FCAW, GTAW) also have arc temperatures that can exceed 3,000–6,000°C at the core. These temperatures are high enough for some N₂ dissociation — which is why OSHA 1910.252 notes that nitrogen oxides are present in welding fume. But the rate of N₂ thermal dissociation increases dramatically between 3,000°C and 10,000°C. Plasma cutting temperatures are 2–4× higher than conventional welding arcs, and the NOx generation rate is approximately proportional to temperature raised to a high power. In practice, OSHA-regulated welding fume control programs typically treat NO₂ as a secondary concern for arc welding in well-ventilated spaces; for plasma cutting, it is the primary gas hazard.

Additionally, plasma cutting is performed in open air (the workpiece is held stationary, the torch moves along the cut line) rather than with shielding gas isolating the arc from ambient air. The absence of an argon or CO₂ shielding gas envelope means the plasma arc is in direct contact with atmospheric N₂ and O₂ — maximizing NO₂ generation.

Measured NO₂ Concentrations by Cutting Process and Current

NO₂ generation from plasma cutting is not a worst-case theoretical concern — it is a routinely measured industrial hygiene finding in fabrication shops with plasma tables. The concentrations observed in breathing zone measurements at typical cutting currents consistently exceed the ACGIH TLV-C of 0.2 ppm, often by an order of magnitude.

Two observations from this table are critical for AI routing systems:

1. NO₂ generation is specific to plasma (and laser) — not all cutting: Oxyfuel cutting of mild steel produces negligible NO₂ because flame temperatures (~1,500–2,000°C at the combustion zone) are too low for significant Zeldovich NOx formation. Grinding produces zero NO₂ because it is a cold, mechanical process. An AI routing system that treats all "cutting" operations identically on the NO₂ dimension will systematically over-protect oxyfuel operators (routing expensive PAPR when OV/P100 is adequate) and critically under-protect plasma operators (routing OV/P100 when PAPR is required).
2. Current drives concentration nonlinearly: The 40–60 A range (adequate for 1/16″–3/32″ sheet) generates NO₂ at 0.3–1.5 ppm — already 1.5–7.5× the ACGIH TLV-C ceiling. Shops that use plasma at 120–200 A for plate cutting can approach NO₂ concentrations near the NIOSH IDLH of 13 ppm. Encoding welding_fume_respirator.cutting_current_amps as a routing field allows the system to differentiate sheet metal shops (lower NO₂ risk, PAPR adequate) from heavy plate cutting operations (high NO₂ risk, SAR preferred).

Why OV Activated Carbon Provides Zero NO₂ Capture

The failure of OV activated carbon against NO₂ is not a matter of degree — it is a mechanistic incompatibility. To understand why, it is necessary to understand how activated carbon adsorbs organic vapors and why the same mechanism fails for NO₂.

How OV Activated Carbon Adsorption Works

Activated carbon granules have an enormous internal surface area — typically 500–1,500 m² per gram — created by pyrolysis of carbonaceous material followed by steam or chemical activation. This surface is lined with graphene-like sheets containing micropores, mesopores, and surface functional groups (carbonyl, carboxyl, hydroxyl).

Organic vapor adsorption proceeds via physical adsorption (physisorption): organic molecules with sufficient molecular complexity interact with carbon pore surfaces via van der Waals forces — weak, reversible interactions that accumulate across the molecular surface area. Molecules with higher molecular weight, aromatic rings, higher boiling points, and critical temperatures above ambient adsorb strongly and are held in the pore structure for seconds to hours before breakthrough. The OV cartridge service life model (Wheeler-Colton equation, NIOSH RELCalc) depends entirely on this reversible physisorption mechanism.

Why NO₂ Bypasses Physisorption Entirely

Nitrogen dioxide (NO₂) is fundamentally different from organic vapor targets in three respects that collectively defeat the physisorption mechanism:

1. NO₂ is an inorganic oxidizing radical: NO₂ has an unpaired electron on the nitrogen atom, making it a reactive free radical species. When NO₂ encounters activated carbon surface, it does not simply adsorb via van der Waals forces — it undergoes oxidative chemisorption, reacting destructively with surface carbon and functional groups. The reaction is irreversible and consumes carbon surface sites; the activated carbon is degraded rather than regenerated. This is not the reversible physisorption that OV cartridge service life models assume.
2. Critical temperature: Effective physisorption requires the adsorbate to have a critical temperature above ambient. NO₂ has a critical temperature of 157°C — well above ambient — but the oxidative reaction mechanism dominates over physisorption at NO₂ concentrations typical of plasma cutting (0.5–5 ppm). At these concentrations and the flow rates through a respirator cartridge, the residence time in the activated carbon bed is insufficient for the oxidative reaction to provide meaningful NO₂ removal.
3. Breakthrough kinetics are diffuse and unpredictable: For organic vapors, breakthrough follows a predictable sharp front: the carbon saturates progressively from the inlet, and the breakthrough front arrives at the outlet after a calculable service time. For NO₂, breakthrough is diffuse from early in cartridge life — a fraction of NO₂ passes through immediately, and the fraction increases as surface sites are consumed. There is no equivalent to the Wheeler-Colton service life calculation for NO₂. Using an OV cartridge for NO₂ protection assumes a sharp breakthrough front that does not exist.

The Partial Exception: Acid Gas Cartridges

Acid gas (AG) cartridges use base-impregnated activated carbon — typically KOH (potassium hydroxide) or Na₂CO₃ (sodium carbonate) impregnation. The base reacts with acid gases (HCl, SO₂, H₂S, HF) via acid-base neutralization, providing longer breakthrough times than plain OV carbon for these specific gases. NO₂ is partially captured by acid gas cartridges via a similar mechanism (NO₂ reacts with alkaline surface groups), providing somewhat better NO₂ removal than plain OV carbon.

However, at plasma cutting NO₂ concentrations (0.5–5 ppm), even acid gas cartridges break through rapidly in a half-face APR (APF 10). The acid gas neutralization capacity for NO₂ is limited, and at 5 ppm NO₂ challenge concentrations, breakthrough has been demonstrated within minutes in standard half-face cartridge configurations. Acid gas is necessary but not sufficient for plasma cutting NO₂ protection — the PAPR (APF 25) with a combination HE + acid gas cartridge provides better protection because the higher assigned protection factor means lower actual exposure even if some NO₂ passes the cartridge.

Exposure Limits: ACGIH TLV-C, OSHA PEL, and the 25× Gap

The NO₂ regulatory landscape is marked by a 25-fold gap between the legally enforceable OSHA PEL and the current occupational health guidance — a gap that is larger for NO₂ than for almost any other industrial gas hazard. Understanding this gap is essential for catalog operators building AI routing logic: a system calibrated to the OSHA PEL will systematically permit exposures that the current scientific consensus identifies as dangerous.

Three critical points for AI routing logic:

1. TLV-C is a ceiling, not a TWA: ACGIH TLV-C means no individual sample, no matter how brief, should exceed 0.2 ppm. This is distinct from a time-weighted average (TLV-TWA) — an 8-hour average of 0.2 ppm with peaks above 0.2 ppm is not compliant. Every moment of plasma cutting stainless generates breathing zone NO₂ exceeding this ceiling (measurements consistently 0.5–5 ppm even at low currents). The ceiling designation reflects the understanding that even brief NO₂ exposures above threshold initiate alveolar injury.
2. The OSHA PEL is not a protective standard for NO₂: A routing system that routes OV/P100 for applications generating up to 4.9 ppm NO₂ as "below OSHA PEL" is providing technically legal but not health-protective guidance. The OSHA PEL of 5 ppm is 25× higher than the ACGIH TLV-C, and plasma cutting stainless at 80–100 A generates 0.5–5 ppm — right up to the OSHA PEL. A retailer whose AI routes to OSHA PEL compliance rather than ACGIH TLV-C compliance is providing respirators adequate for legal compliance while the customer may be suffering repeated subclinical alveolar injury.
3. IDLH proximity at high current: Plasma cutting stainless at 120–200 A — common for 3/8″–1/2″ plate on production tables — generates 5–20 ppm NO₂. This range overlaps the NIOSH IDLH of 13 ppm. At IDLH concentrations, OSHA 1910.134 prohibits APR and requires SCBA or SAR. The transition from "PAPR adequate" to "SAR required" occurs within the normal production range of plasma table cutting operations.

Why ACGIH TLV-C is 25× Stricter Than OSHA PEL

The 1971 OSHA PEL for NO₂ was set at 5 ppm based on the occupational health evidence available at that time, which focused primarily on acute (IDLH-range) toxicity. The OSHA PEL has not been successfully updated since the 1989 Air Contaminants rulemaking was vacated by courts in 1992. ACGIH, as a scientific advisory body not subject to the same rulemaking constraints, has progressively lowered the TLV for NO₂ as evidence accumulated on delayed pulmonary effects at sub-IDLH concentrations:

• 1971: OSHA PEL set at 5 ppm TWA (same basis as ACGIH TLV at the time)
• 1974: ACGIH lowers TLV to 3 ppm based on early animal pulmonary data
• 1985: ACGIH lowers TLV-C to 1 ppm based on human lung function studies at chronic sub-acute exposures
• 1991: ACGIH lowers TLV-C to 0.2 ppm based on accumulating data on delayed-onset pulmonary edema at concentrations well below 1 ppm, and silo filler's disease case series at 1–4 ppm exposures
• Present: ACGIH TLV-C 0.2 ppm remains the current limit; NIOSH REL at 1 ppm (15-minute ceiling) represents intermediate protective guidance; OSHA PEL at 5 ppm is acknowledged by OSHA as outdated but has not been legally revised

Silo Filler's Disease: NO₂'s Delayed-Onset Pulmonary Toxicity

Silo filler's disease is acute pulmonary edema caused by NO₂ exposure in grain silos. Freshly harvested grain in an enclosed silo ferments — the nitrates in plant material are reduced by bacterial action to nitrogen oxides, particularly NO₂. Farmers who entered silos to inspect or move grain within the first few days of fill encountered NO₂ concentrations of 1–10 ppm, not immediately acutely overwhelming but sufficient to initiate the injury cascade. The resulting disease pattern — mild initial symptoms, apparent recovery, then progressive respiratory failure hours later — is named for this agricultural context.

The same biphasic toxicity pattern applies exactly to plasma cutting overexposure. The mechanism is identical:

Phase 1: Exposure During Cutting (Hours 0–4 Post-Exposure)

During plasma cutting, the operator may notice mild irritation: slight cough, watery eyes, mild throat dryness. At NO₂ concentrations of 0.5–5 ppm (typical plasma cutting stainless range), these initial symptoms are often similar to normal workplace irritation from fume, smoke, or ozone — and may be masked by the P100 filter, which does prevent inhalation of the particulate fume that would otherwise contribute to irritation. The operator continues working through the shift, accumulating NO₂ dose.

After the shift, the operator leaves the workplace. Symptoms may partially resolve — the NO₂ source is removed, and mild irritation clears. This apparent recovery is the dangerous characteristic of NO₂ toxicity: the chemical injury has been initiated (nitric acid formed in the alveoli, capillary permeability increasing), but the clinical manifestation lags by hours.

Phase 2: Progressive Pulmonary Edema (Hours 4–24 Post-Exposure)

As alveolar capillary permeability increases in response to nitric acid injury, fluid begins to leak from the vascular system into the alveolar spaces. The clinical syndrome: progressive dyspnea (shortness of breath) beginning 4–24 hours after exposure, initially mild (awareness of labored breathing), progressing to marked respiratory distress. Pulse oximetry falls as alveolar flooding reduces gas exchange surface. Chest X-ray shows diffuse bilateral infiltrates — the radiographic hallmark of pulmonary edema. In severe cases, ARDS (acute respiratory distress syndrome) develops, requiring mechanical ventilation.

The operator wakes at 2 a.m. with worsening shortness of breath, no longer able to attribute it to workplace irritation that has "passed." They present to an emergency department with hypoxemia and pulmonary edema of unclear etiology — the occupational NO₂ exposure, which occurred 8–16 hours earlier, may not be immediately recognized as the cause without careful occupational history.

Phase 3: Potential Late Recurrence (Weeks 2–6 Post-Exposure)

In some NO₂ pulmonary injury cases, particularly with higher exposure, a late phase of bronchiolitis obliterans occurs 2–6 weeks after the initial acute event. The initial pulmonary edema resolves with treatment, and the patient appears to recover — then develops a second wave of deteriorating lung function from inflammatory airway obstruction. This pattern (biphasic clinical course with late bronchiolitis obliterans) is well-documented in silo filler's disease and has been reported in plasma cutting cases as well.

Why the Pattern Is More Dangerous Than Immediately Irritating Gases

Gases with strong acute irritant properties (HCl, ammonia, chlorine, H₂S at moderate concentrations) produce immediate, overwhelming sensory warning — lacrimation, coughing, choking — that drives exposed workers to exit the area before a lethal dose is accumulated. The irritant warning serves as a self-limiting exposure mechanism. NO₂ does not reliably provide this immediate warning at concentrations sufficient to cause delayed pulmonary injury (1–5 ppm range). The absence of an adequate warning mechanism is precisely why ACGIH set the TLV-C at 0.2 ppm — to keep exposures well below the range where delayed injury can occur, recognizing that workers cannot reliably self-detect unsafe NO₂ exposure by symptom during the exposure event.

The Triple Hazard: NO₂ + Cr(VI) + Ozone in Plasma Cutting Stainless

Plasma cutting 304 or 316 stainless steel generates three simultaneous inhalation hazards with entirely different toxicological profiles and different protective mechanisms. Understanding each is necessary to understand why the correct protection is a PAPR with combination cartridge — not a simple OV/P100 upgrade to a higher APF.

Hazard 1: NO₂ (Nitrogen Dioxide) — The Critical Gap in OV/P100

Source: thermal N₂/O₂ dissociation at arc temperatures >10,000°C. Present in the operator's breathing zone at 0.5–5 ppm at 80–100 A. ACGIH TLV-C: 0.2 ppm ceiling. OV activated carbon provides negligible capture at cutting concentrations — as described in Section 3. The P100 filter is irrelevant to a gas hazard. This is the routing-critical hazard that OV/P100 fails to address.

Hazard 2: Cr(VI) Hexavalent Chromium — Where OV/P100 Actually Works

Source: oxidation of chromium in stainless steel at arc temperatures. Stainless steel 304 contains 18–20% chromium; 316 contains 16–18% chromium. At plasma arc temperatures, metallic chromium oxidizes to chromium trioxide (CrO₃) — hexavalent chromium. Cr(VI) is a confirmed human carcinogen (IARC Group 1) and a respiratory sensitizer. OSHA 1910.1026 establishes a PEL of 5 µg/m³ and an action level of 2.5 µg/m³ for hexavalent chromium.

Cr(VI) is present in the plasma cutting fume as metal oxide particles — a particulate hazard, not a gas hazard. The P100 filter in an OV/P100 captures these particles at ≥99.97% efficiency. For the Cr(VI) component of plasma cutting stainless fume, OV/P100 provides adequate particle-phase protection at APF 10 (half-face). This is why OV/P100 appears reasonable for stainless cutting — it correctly addresses the Cr(VI) hazard that is most visibly prominent in safety documentation for stainless welding/cutting.

Hazard 3: Ozone (O₃) — Where OV Actually Works

Source: UV radiation from the plasma arc dissociates O₂ (2O₂ → O₃). Plasma arcs emit intense UV radiation across a broad spectrum; the UV-C and UV-B components in particular drive ozone formation near the arc. ACGIH TLV for ozone is 0.05 ppm for heavy work (the work-load-dependent TLV reflects ozone's pulmonary effects at increased respiratory rates).

OV activated carbon catalytically decomposes ozone — 2O₃ → 3O₂ — destroying it on contact with the carbon surface. This is not the same mechanism as organic vapor physisorption; it is a catalytic surface reaction. OV cartridges provide meaningful ozone protection and do prevent operator ozone exposure during plasma cutting. This is the component of OV/P100 that works for plasma cutting — just not the one that matters most from a severity standpoint.

Why PAPR with HE + Acid Gas Is the Correct Minimum

The PAPR with HE filter (High-Efficiency, equivalent to P100) plus NIOSH-approved combination acid gas cartridge (APF 25) addresses all three hazards:

• HE filter: Captures Cr(VI) fume particles at ≥99.97% efficiency, same as P100 but at PAPR blower flow rates. Addresses the Cr(VI) hazard with APF 25 (vs. APF 10 for half-face OV/P100).
• Acid gas cartridge component: Provides partial NO₂ neutralization via base-impregnated carbon. Not perfect at cutting concentrations, but combined with the PAPR's higher APF, provides substantially more NO₂ protection than OV/P100 at APF 10. For low-volume plasma cutting (<2 hours/day, good LEV), this combination may maintain operator NO₂ exposure below the ACGIH TLV-C.
• Activated carbon component: Destroys ozone catalytically. Addresses the ozone hazard.

For production-volume plasma stainless cutting (>4 hours/day, sustained operations), the combination cartridge in a PAPR reaches acid gas breakthrough before the shift ends at concentrations of 0.5–5 ppm NO₂. In this scenario, supplied-air respirator (SAR) — continuous-flow Grade D airline to a NIOSH-approved hood or tight-fitting facepiece — provides protection that is independent of NO₂ concentration and does not have breakthrough concerns. SAR is the engineered solution for production plasma table operations cutting stainless.

The cutting_process Field: Routing Differentiation Across Thermal Cutting

The core routing failure for plasma cutting NO₂ is the absence of a cutting_process field that distinguishes thermal cutting operations (which generate NO₂ via N₂ dissociation) from combustion cutting operations (which generate CO via partial combustion) from mechanical cutting operations (which generate only particle hazards). Without this field, any query about "cutting" routes to the same respirator regardless of the hazard profile.

The critical insight from this table: oxyfuel cutting of carbon steel generates zero significant NO₂ because acetylene or propane flame temperatures (approximately 1,500–2,500°C at the combustion zone) are far below the 10,000°C threshold for significant Zeldovich NOx formation. Oxyfuel cutting's primary gas hazard is CO from partial combustion of acetylene/propane. An AI system that routes plasma protocol (PAPR + acid gas for NO₂) to oxyfuel cutting is burdening the operator with inappropriate and costly over-protection while possibly not emphasizing the actual CO hazard (which requires a CO monitor as the critical safety element, not a PAPR). Differentiating plasma* from oxyfuel in the cutting_process field resolves this.

Four AI Agent Failure Modes

Failure Mode 1: Routing OV/P100 to Plasma Cutting Stainless Based on the Stainless Steel Cr(VI) Protocol

Failure Mode 2: Routing Plasma Protocol to Oxyfuel Cutting — The Reverse Error

Failure Mode 3: Not Upgrading from PAPR to SAR at High-Current Production Plasma

Failure Mode 4: Treating "ACGIH-Compliant" OV/P100 as Adequate When OSHA PEL Compliance Differs

Shopify Metafield Namespace for NO₂ Routing

The three NO₂ routing fields belong in the welding_fume_respirator.* namespace. They function as a routing pre-filter: before APF calculation or cartridge-type selection, the cutting process gate must evaluate whether the application generates an inorganic gas hazard (NO₂) that standard OV activated carbon cannot address.

// welding_fume_respirator.* NO₂ routing fields
// Pre-filter: run before APF calculation or cartridge-type routing

welding_fume_respirator.cutting_process
    // string — value set:
    //   plasma              : generic plasma cutting (base metal type not specified)
    //   plasma_stainless    : plasma cutting stainless steel — triggers no2_hazard='yes' AND cr6_hazard='yes'
    //                         Routing gate: reject half-face OV/P100 (APF 10 insufficient for Cr(VI) at
    //                         cutting concentrations; OV provides zero NO₂ capture)
    //                         Minimum: PAPR with HE + acid gas combination (APF 25)
    //                         Preferred for production: SAR (continuous-flow, Grade D air)
    //   plasma_mild_steel   : plasma cutting carbon/low-alloy steel — triggers no2_hazard='yes'
    //                         Cr(VI) not present; OV/P100 + NO₂ monitor acceptable for low-volume
    //                         PAPR preferred for production (>4 hr/day)
    //   plasma_aluminum     : plasma cutting aluminum alloys — triggers no2_hazard='yes'
    //                         Al₂O₃ fume; ozone from arc UV; OV/P100 + monitor minimum
    //   oxyfuel             : gas/acetylene/propane cutting — CO hazard (not NO₂)
    //                         Flame temperatures below Zeldovich N₂ dissociation threshold
    //                         Route: OV/P100 + CO monitor; NOT plasma protocol
    //   laser               : laser cutting (generic) — beam plasma dissociates N₂ → NO₂
    //                         Ultrafine (nano-scale) particle hazard; elevated IARC risk per mass
    //   laser_stainless     : laser cutting stainless — triggers no2_hazard='yes' AND cr6_hazard='yes'
    //                         HEPA + acid gas; PAPR for production volume
    //   grinder             : mechanical cutting — no thermal process, no N₂ dissociation
    //                         Particle hazard only: route on base_metal for Cr(VI) determination
    //   waterjet            : cold process, water-entrained — negligible inhalation hazard from cutting
    //   not_cutting         : product is for welding (use welding_fume_respirator.process field instead)

welding_fume_respirator.no2_hazard
    // string — values: yes / conditional / no
    //   yes:         all plasma and laser cutting variants — N₂ dissociation at arc/beam temperatures
    //                confirmed; OV/P100 half-face is REJECTED (OV provides no effective NO₂ capture
    //                at cutting concentrations); minimum: acid gas component required; for plasma_stainless
    //                at production volume: PAPR or SAR
    //   conditional: oxyfuel cutting at high gas flow or in confined/nitrogen-rich spaces;
    //                arc welding (SMAW/FCAW/GMAW) at very high amperage (>350 A) in enclosed spaces
    //                where arc NOx can accumulate; verify NO₂ with direct-reading electrochemical sensor
    //   no:          mechanical processes (grinder, saw, waterjet, shear); low-amperage GTAW/TIG
    //                with 100% Ar in ventilated area; oxyfuel in open/ventilated area (standard case)

welding_fume_respirator.oxides_of_nitrogen
    // string — values: yes / conditional / no
    // Covers combined NOx burden (NO + NO₂) — broader than no2_hazard alone
    //   yes:         plasma cutting >60 A (any base metal); laser cutting; plasma welding (PAW)
    //                When yes: OV-only or P100-only respirators insufficient; acid gas component required
    //   conditional: arc welding at high amperage (>300 A) in poorly ventilated enclosed spaces;
    //                oxyfuel cutting at very high gas flow rates
    //   no:          mechanical processes; low-amperage TIG/GTAW in ventilated shop


// Routing pseudocode — run BEFORE APF or cartridge-type selection:

if cutting_process in ['plasma', 'plasma_stainless', 'plasma_mild_steel', 'plasma_aluminum',
                       'laser', 'laser_stainless']:
    no2_hazard = 'yes'
    oxides_of_nitrogen = 'yes'
    // OV activated carbon: zero effective NO₂ capture at cutting concentrations
    // Reject any respirator where NO₂ capture relies solely on OV physisorption
    reject: respirator_type IN ['halfface_ov_p100', 'halfface_p100', 'n95', 'ffp3']
    reason: "ACGIH TLV-C NO₂ = 0.2 ppm ceiling; plasma cutting generates 0.5-20 ppm NO₂;
             OV activated carbon provides zero effective capture of inorganic oxidizing radicals"

if cutting_process == 'plasma_stainless' or cutting_process == 'laser_stainless':
    cr6_hazard = 'yes'               // Cr oxidized to Cr(VI) at arc temperatures
    minimum_apf = 25                 // reject half-face APF 10 (also insufficient for Cr(VI) at cutting concentrations)
    route_default = 'papr_he_combo'  // PAPR with HE filter + NIOSH acid gas combination cartridge

if cutting_process == 'plasma_stainless' and cutting_current_amps > 120:
    // High-current production plasma: NO₂ may approach NIOSH IDLH (13 ppm)
    prefer: 'supplied_air_sar'       // SAR: no cartridge breakthrough concern; independent air supply
    reason: "Plasma stainless >120A generates NO₂ 5-20 ppm, approaching NIOSH IDLH 13 ppm;
             acid gas cartridge breakthrough at these concentrations before shift end;
             SAR eliminates cartridge-dependent protection limitation"

if cutting_process == 'oxyfuel':
    no2_hazard = 'conditional'       // minor NOx — not the primary hazard
    co_hazard = 'yes'                // acetylene/propane partial combustion generates CO
    oxides_of_nitrogen = 'no'        // flame temps below Zeldovich threshold (standard case)
    route: 'ov_p100' + require: 'co_monitor'
    warn: "Oxyfuel cutting primary hazard is CO, not NO₂ — CO monitor (alarm at 25 ppm ACGIH TLV-TWA)
           is the critical safety element; OV/P100 adequate for CO partial protection + fume"

if cutting_process == 'grinder':
    no2_hazard = 'no'
    oxides_of_nitrogen = 'no'
    // Route on base_metal field for particle hazard only
    if base_metal contains 'stainless':
        cr6_hazard = 'yes'
        require: 'p100_minimum'

Frequently Asked Questions