Reference
Comparison & Cheat-Sheet
Everything on one page: the master technology matrix, a "which tool answers which question" decision guide, the cross-sensitivity summary, and a print-friendly one-pager for the truck binder.
OPS TECH quick reference for both levels
Field Tip — print the cheat sheet
This page is formatted so that File → Print drops the navigation and callouts-clutter and lays the tables out cleanly for a binder. The one-page cheat sheet at the bottom is the most condensed version.
Master comparison matrix
| Technology | Detects | Misses / blind to | Sample phase | Response | Bump / Cal interval | Cost | Training |
|---|---|---|---|---|---|---|---|
| Electrochemical | O₂, CO, H₂S, Cl₂, NH₃, HCN, SO₂, NO₂, PH₃ (one gas per sensor) | Anything without a fitted sensor; unknowns | Gas/vapor | Seconds (T90 ~sec–30s) | Bump daily / cal ~monthly | Low | Low |
| Catalytic bead LEL | Combustible gases/vapors incl. H₂ (%LEL) | Needs O₂; poisoned by silicones/sulfur; no ID | Gas/vapor | Seconds | Bump daily / cal ~monthly | Low | Low |
| Infrared (NDIR) LEL/CO₂ | Hydrocarbons (%LEL), CO₂; works in inert/low-O₂ | Hydrogen (blind); no ID; optics fog | Gas/vapor | Seconds | Bump daily / cal ~monthly | Low–Med | Low |
| PID | Broad VOCs (IP < lamp), ppb–ppm | Methane, CO, CO₂, HCN; no ID; humidity quench | Gas/vapor | Seconds | Bump daily / cal ~monthly | Med | Low–Med |
| FID | Total organics incl. methane | All inorganics (CO, NH₃, Cl₂, H₂); no ID; needs H₂ fuel | Gas/vapor | Seconds (after warm-up) | Functional check daily / cal per mfr | Med–High | Med |
| Colorimetric tubes | One specific chemical per tube (huge menu) | Continuous monitoring; ~±25% accuracy | Gas/vapor | ~1 min (strokes) | No cal; check expiry + pump leak | Low | Low–Med |
| IMS | CWAs (nerve/blister), some TICs | Vapor only; library-limited; many false + | Gas/vapor | Seconds | Auto self-cal; sieve pack + source checks | High | Med–High |
| Raman | Bulk solids/liquids, through clear containers | Metals; dilute aqueous; fluoresces on dark; ignition risk | Solid/liquid (bulk) | Seconds–min | Auto perf-verify (polystyrene) | High | Med–High |
| FTIR | Bulk solids/liquids incl. aqueous, dark/colored | Metals/simple salts; needs contact/handling | Solid/liquid (bulk, contact) | Seconds–min | Auto perf-verify (polystyrene) + background | High | Med–High |
| GC-MS | Volatiles & mixtures — confirmatory ID | Non-volatiles/metals; slow; not real-time | Vapor/liquid (volatiles) | Minutes–tens of min | Tune/verify; blanks; consumables | Very High | High |
| Radiation (GM/scint/RIID) | α/β/γ/neutron; dose rate; isotope ID | Non-radioactive hazards; alpha easily missed | Radiation field / contamination | Seconds (dwell for ID) | Daily source check / cal ≥ annually | Low–High | Low–High |
| Wet chem / papers | Hazard class: pH, oxidizer, fluoride, liquid agent | Identity (classify only); false positives | Liquid/solid (moisten) | Seconds | No cal; check expiry | Low | Low |
Which tool for which question?
Start from the question you're actually trying to answer, not the tool you happen to be holding.
| The question | Reach for… | Watch out for |
|---|---|---|
| Is there radiation? | PRD to detect → survey meter for dose rate → RIID for isotope | PRD isn't a dose meter; NORM/medical false alarms; alpha easily missed |
| Is there enough oxygen? | O₂ electrochemical sensor (multi-gas) | Altitude/pressure shifts reading; low O₂ invalidates the cat-bead LEL |
| Is it flammable? | Catalytic bead LEL (normal air, incl. H₂) — or IR LEL in inert/poison-heavy spaces | Cat bead: low O₂, poisoning, over-range roll. IR: blind to hydrogen |
| Are there toxic gases? | EC toxic sensors + PID (broad VOC) + tubes to confirm | Cross-sensitivity; PID blind to methane/CO/HCN; sticky gases (HF) |
| Is there volatile organic vapor? | PID (broad survey); FID if methane/light hydrocarbons matter | Survey tools, not identifiers; PID misses methane, FID needs H₂ fuel |
| Is it a chemical warfare agent? | IMS (vapor) + M8/M9 paper (liquid) + agent tubes — corroborate | IMS false positives (exhaust/cleaners/perfume); M8/M9 false + (fuels, brake fluid, DEET) |
| What hazard CLASS is this liquid/solid? | Classifier strips — pH, oxidizer, fluoride, agent | Classify only, not identify; moisten dry products; false positives |
| What exactly IS this bulk solid/liquid? | Raman (through container, light-colored) and/or FTIR (dark/colored, aqueous) | Raman: fluorescence, metals, dilute aqueous, ignition risk. FTIR: needs contact, weak on metals/salts |
| What exactly IS this vapor / mixture? (confirmatory) | GC-MS | Slow, volatiles-biased, consumable- and training-heavy — an escalation, not a first move |
| Is it corrosive? | pH paper / classifier strip (moisten dry products) | pH gives class not identity; dry-on-dry reads falsely neutral |
| Could HF be involved? | Fluoride paper + HF tubes — distrust gas-monitor numbers | HF sticks to tubing/inlets and is badly under-reported electronically |
✓ Remember — the workflow
Survey (rad, O₂, LEL, PID) → characterize (papers, tubes, IMS) → identify (Raman/FTIR → GC-MS). Corroborate anything consequential with a second, independent technology.
Cross-sensitivity & blind-spot master summary
| Tool / sensor | Reads the wrong thing / is blind to… | Direction of danger |
|---|---|---|
| CO electrochemical | Hydrogen, H₂S, unsaturated hydrocarbons read as "CO" | False high (or misattributed) |
| H₂S electrochemical | SO₂, mercaptans, methanol cross-read | False high |
| HCN electrochemical | H₂S, SO₂, NO₂, HCl; drifty | False high / unreliable |
| Cl₂ / NO₂ (oxidizing) EC | Reducing gases (H₂S, SO₂) can null them | False low (masking) |
| O₂ electrochemical | Altitude/pressure; high CO₂ | False low/high O₂ |
| Catalytic bead LEL | Low O₂; silicone/sulfur/lead poisons; over-range roll | False low — deadly |
| Infrared LEL | Hydrogen (totally blind); optics condensation | False low/zero on H₂ |
| PID | Methane, CO, CO₂, HCN (blind); humidity quenches | False low / false "clear" |
| FID | All inorganics; flame-out drops to baseline | False "clear" on inorganics |
| Colorimetric tubes | Interferents printed on insert; ±25% | False high or low |
| IMS | Exhaust, cleaners, perfume, wax → false CWA; masking | False high (& occasional false low) |
| Raman | Dark/colored (fluorescence), metals, dilute aqueous | No result / no match |
| FTIR | Metals, simple salts; crystal carryover | No result / cross-contam false ID |
| Radiation (basic GM) | Saturation/fold-back in intense field; NORM/medical | False low in strong field; nuisance alarms |
| M8/M9 paper | Petroleum, brake fluid, DEET, solvents; liquid-only | False positive agent |
Failure modes that kill — commit these to memory
⚠ Warning — the deadly five
- Poisoned catalytic LEL bead reads LOW — tells you a flammable atmosphere is safe. Bump daily; keep silicones away.
- Dead electrochemical sensor reads ZERO — looks like clean air. Only the daily bump catches it.
- PID is blind to methane/natural gas, CO, and HCN — a PID zero is not "all clear."
- Infrared LEL is blind to hydrogen — a fatal gap in battery rooms and lithium fires.
- Trusting a single technology / single reading — every tool has a blind spot; corroborate.
Bonus rad killers: a basic GM meter reading falsely low in an intense field, and missing alpha contamination with the wrong probe/technique.
One-page cheat sheet
Optimized for printing (File → Print). The section below is the condensed field reference.
HAZMAT METERING — FIELD CHEAT SHEET
Training reference — typical values; manuals, AHJ & SOPs govern.
Training reference — typical values; manuals, AHJ & SOPs govern.
Monitoring priority & workflow
- Priority order: Radiation → Oxygen → Flammability → Toxics.
- Workflow: Survey (rad, O₂, LEL, PID) → Characterize (papers, tubes, IMS) → Identify (Raman/FTIR → GC-MS).
- Golden rule: no single meter tells the whole story — corroborate with a second technology.
Action levels (typical — SOPs govern)
- O₂: normal 20.9%; 19.5–23.5% band; <19.5% deficient (LEL unreliable); >23.5% enriched.
- LEL: common first action at 10% LEL; evacuate by ~20–25% per SOP.
- Toxic: compare to PEL/TLV for work limits; IDLH = get out / max protection.
- Radiation: investigate above background; turn-back per rad SOP.
Cal & readiness in one line each
- Gas monitors (EC / cat-bead / IR / PID / FID): bump before each day's use (ISEA); full cal per mfr (~monthly); cal now after failed bump, drop, poison, or high exposure.
- Colorimetric tubes / papers: no cal — check expiry (refrigerate tubes), leak-check pump, moisten dry products.
- IMS: auto self-cal; maintain sieve pack; corroborate every alarm.
- Raman / FTIR: auto performance verification (polystyrene); FTIR also needs a background scan & clean crystal.
- GC-MS: tune/verify + run blanks; confirmatory, not real-time.
- Radiation: daily check-source response test; professional calibration at least annually.
Deadly blind spots
- Poisoned cat-bead LEL → reads LOW (silicones, sulfur, low O₂).
- Dead EC sensor → reads ZERO (looks clean).
- PID blind: methane/natural gas, CO, CO₂, HCN.
- IR LEL blind: hydrogen (battery rooms, lithium fires).
- Basic GM: can read low in an intense field; alpha easily missed.
- IMS & M8/M9: false-positive on everyday products — corroborate.
Which tool for which question
- Rad? PRD → survey meter → RIID.
- Flammable? Cat-bead LEL (normal air/H₂) or IR LEL (inert/poison-heavy).
- Toxic gas? EC sensors + PID + confirm with tubes.
- CWA? IMS (vapor) + M8/M9 (liquid) + agent tubes — corroborate.
- Hazard class of liquid/solid? Classifier strips (pH/oxidizer/fluoride/agent).
- What is it? Raman (through container) / FTIR (dark, aqueous) → GC-MS to confirm.
Training reference only. Not a substitute for hands-on training, manufacturer manuals, the AHJ, or department SOPs. All values typical/representative.