Reference

Glossary

Every acronym and term used in this guide, defined in plain language and alphabetized. Each entry has an anchor link you can share.

A

AEGL (Acute Exposure Guideline Levels): EPA emergency exposure guidelines for the public, published in three severity tiers (AEGL-1/2/3) across multiple exposure durations (10 min to 8 hr). Used for protective-action and evacuation planning. See Core Concepts.
Alpha (α) radiation: A heavy charged particle stopped by paper, skin, or a few cm of air — little external hazard, but a serious internal hazard if inhaled or ingested. Hard to detect; needs a thin-window probe held very close. See Radiation.
ATR (Attenuated Total Reflectance): The sampling method in most handheld FTIR instruments: the sample is pressed onto a hard crystal (e.g., diamond) and the IR beam probes the material in contact with it. Requires direct sample contact.
Action level: A pre-decided instrument reading at which you take a defined action (back out, upgrade PPE, expand the zone). Set by SOP/AHJ. See Home.

B

Beta (β) radiation: A fast electron stopped by thin metal/plastic. Skin and internal hazard; needs a thin/open-window probe. See Radiation.
Bump test (functional test): A brief exposure to a known target gas above the alarm setpoint to confirm the sensor responds and the alarm activates. Does not adjust the instrument. Recommended before each day's use (ISEA position). Contrast with calibration. See Core Concepts.

C

Calibration (full / span): A two-point adjustment: zero in clean air, then expose to a certified span gas and adjust the instrument's scale to match. Corrects sensor drift. Done on a schedule (commonly monthly). See Core Concepts.
Catalytic bead (pellistor): An LEL sensor that burns combustible gas on a heated catalytic bead and measures the heat as %LEL. Needs oxygen; vulnerable to poisoning. See Catalytic Bead LEL.
Ceiling (C) limit: An exposure concentration that must never be exceeded at any instant — no averaging permitted. See Core Concepts.
Check source: A small, low-activity radioactive source used for a daily/pre-use response check of a radiation instrument — the rad equivalent of a bump test. See Radiation.
Clear-down (recovery) time: The time a sensor takes to return to zero after gas is removed. Can be much longer than the rise time for "sticky" gases; a saturated sensor may under-report during recovery.
Correction factor (CF) / Response factor: A multiplier that converts a reading (in calibration-gas equivalents) into the true concentration of a known chemical. Only valid for a known single chemical, never an unknown or mixture. See Core Concepts.
Contamination (radiological): Radioactive material physically on a person, gear, or surface — it "follows you" until removed/deconned. Distinct from dose. Measured with a thin-window/pancake probe. See Radiation.
Cross-sensitivity: When a sensor responds to a gas other than its target, producing a reading on the "wrong" channel (positive or negative). See Electrochemical.
CWA (Chemical Warfare Agent): Nerve, blister, blood, and choking agents. Detected in the field by IMS, M8/M9 paper, and colorimetric agent tubes.

D

Datalogging: Continuous timestamped recording of readings to instrument memory, used for exposure documentation and reconstruction. See Core Concepts.
Dead time (radiation): The brief interval after a detection event during which a detector (e.g., a GM tube) can't register another. At high fields this causes saturation and, in basic tubes, possible fold-back to a false-low reading.
Diffusion sampling: Letting ambient air reach the sensor on its own through vents (no pump). Samples only the air immediately around the instrument. Contrast with pumped sampling. See Core Concepts.
Dopant: A reagent gas added in an IMS ionization region to steer selectivity and reduce interference.
Dose (radiation): Energy absorbed by the body from a radiation field — a function of being near a source. Managed by time, distance, shielding. Distinct from contamination. See Radiation.
Dosimeter: A device that measures a person's accumulated radiation dose over time (as opposed to instantaneous dose rate).

E

Electrochemical (EC) sensor: A gas sensor that produces a current proportional to concentration via a chemical reaction at an electrode. Used for O₂ and toxic gases. See Electrochemical Sensors.
Energy compensation (GM): A filter on a GM detector that flattens its response across gamma energies so the displayed dose rate is accurate. See Radiation.
ERG (Emergency Response Guidebook): The DOT/TC/SCT guidebook for initial actions and isolation/evacuation distances at transportation incidents. Assumed knowledge at Ops/Technician level.
ERPG (Emergency Response Planning Guidelines): AIHA community emergency exposure tiers (ERPG-1/2/3) for a 1-hour exposure, used for public protective actions. See Core Concepts.
eV (electron-volt): A small unit of energy. Used to express both a PID lamp's photon energy (9.8 / 10.6 / 11.7 eV) and a molecule's ionization potential — the two numbers you compare to know what a PID can see.

F

FID (Flame Ionization Detector): Measures total organic vapor (including methane) by burning the sample in a hydrogen flame and counting the ions produced. Blind to inorganics. See FID.
Fluorescence (Raman interference): Bright glow emitted by some (often dark/colored) samples under the Raman laser that swamps the faint Raman signal, producing an unusable spectrum. See Raman.
FTIR (Fourier-Transform Infrared spectroscopy): Identifies substances by their infrared absorption fingerprint, typically via ATR contact sampling. Strong on dark/aqueous samples; needs contact. See FTIR.

G

Gamma (γ) radiation: A penetrating photon; whole-body external hazard needing dense shielding. Easy to detect at a distance. See Radiation.
GC-MS (Gas Chromatography–Mass Spectrometry): Confirmatory identification that first separates a mixture (GC) then fingerprints each component by mass (MS). Slow, volatiles-biased. See GC-MS.
GM tube (Geiger-Müller): A gas-filled radiation detector that pulses ("clicks") on each ionizing event; used for dose-rate survey and contamination probes. See Radiation.

H

Headspace sampling: Sampling the vapor above a material in a sealed container (rather than the bulk), commonly used to feed volatiles into a GC-MS.
HF (Hydrogen fluoride / hydrofluoric acid): A highly toxic, "sticky" compound that adsorbs onto sample tubing and instrument inlets, causing gas monitors to under-report it. Cross-check with fluoride paper and HF tubes.
Hygroscopic: Readily absorbs moisture from the air. The 11.7 eV PID lamp window is hygroscopic, which shortens its life.

I

IDLH (Immediately Dangerous to Life or Health): NIOSH-published level of exposure that could cause death, permanent harm, or prevent self-escape — the "get out / maximum protection only" threshold. See Core Concepts.
IMS (Ion Mobility Spectrometry): Detects chemicals (notably CWAs) by how fast their ions drift through air. Fast and sensitive but prone to false positives. See IMS.
IP (Ionization Potential): The energy (in eV) needed to knock an electron off a molecule. A PID can only detect molecules whose IP is below its lamp energy. See PID.
ISEA position (bump/cal): The Safety Equipment Association's guidance that gas detectors should be bump tested before each day's use, with calibration verified regularly. Referenced throughout this guide.
Isobutylene: The near-universal calibration reference gas for PIDs; readings are reported in "isobutylene equivalents" and converted with correction factors.

L

LEL (Lower Explosive Limit) / LFL: The lowest concentration of a gas/vapor in air that will burn/explode. Combustible sensors read as %LEL (percent of that limit), so 100% LEL = the bottom of the flammable range. See Catalytic Bead LEL.

M

M8 / M9 paper: Chemical-agent detection papers for liquid agent. M8 differentiates G-nerve/V-nerve/blister by color; M9 tape turns red for any liquid agent without differentiating. Both false-positive on fuels/solvents. See Wet Chemistry.
Mixture deconvolution: Algorithms in Raman/FTIR/GC-MS that separate a spectrum/sample into multiple library components. Reliable mainly for major components (typically >~10%).

N

NDIR (Non-Dispersive Infrared): An infrared sensor that measures how much IR a gas absorbs; used for LEL and CO₂. Poison-immune and works in inert atmospheres but blind to hydrogen. See Infrared LEL.
Neutron radiation: Uncharged particle radiation requiring a dedicated detector (He-3 or Li-based) with a moderator; often signals fissile/special nuclear material. See Radiation.
NFPA 470: The consolidated NFPA standard for hazardous materials/WMD response competencies (incorporating the former 472/473/etc.), defining Awareness, Operations, and Technician levels. This guide targets Operations and Technician.
NIST library: A large reference database of mass spectra used by GC-MS to match and identify compounds.
NORM (Naturally Occurring Radioactive Material): Everyday materials with natural radioactivity (granite, fertilizer, ceramics, bananas) that routinely cause nuisance radiation alarms. See Radiation.

O

Oxidizer: A material that supports/accelerates combustion and can react violently with fuels/organics. Screened with oxidizer papers/strips.

P

Pancake probe: A wide, thin-window GM probe used for alpha/beta/gamma contamination surveys. The window is fragile.
PEL (Permissible Exposure Limit): OSHA's legally enforceable worker-exposure limit, usually an 8-hour average. See Core Concepts.
PID (Photoionization Detector): A broadband VOC survey sensor that ionizes molecules with a UV lamp. Blind to methane/CO/CO₂/HCN; a survey tool, not an identifier. See PID.
Poisoning (sensor): Permanent degradation of a sensor's active element by certain chemicals — most importantly silicones on a catalytic bead, which makes it read low. Contrast with temporary inhibition.
PRD (Personal Radiation Detector): A pocket/pager radiation detector for constant screening — very sensitive to changes but not a dose-rate meter. See Radiation.
Pumped sampling: Using a pump to draw a sample through tubing from a remote point (e.g., a confined space) before entry. Watch travel time down the line. See Core Concepts.
Polystyrene reference: A standard with well-known spectral peaks used for automatic performance verification of Raman and FTIR instruments.

R

Raman spectroscopy: Identifies bulk solids/liquids by the color-shift of scattered laser light — often through clear containers. Blinded by fluorescence; laser can ignite dark energetics. See Raman.
Relative response: How large a reading a sensor gives for a chemical compared to its calibration gas. A low relative response (high correction factor) means the sensor under-reports that chemical.
RIID (Radioisotope Identification Device): A spectroscopic radiation instrument that reads the gamma energy spectrum to name the isotope; subject to misidentification with short counts, shielding, or NORM. See Radiation.

S

Scintillator: A radiation detector (often NaI) that flashes light when radiation hits it; very sensitive for search. See Radiation.
Setpoint (alarm): The concentration at which an instrument alarms. Gases often have low/high plus TWA/STEL setpoints. See Core Concepts.
SERS (Surface-Enhanced Raman Spectroscopy): A Raman variant using engineered metallic substrates to amplify signal for low/trace concentrations; needs special consumables. See Raman.
Sieve pack: An internal drying/scrubbing consumable in an IMS that keeps the drift gas clean and dry; must be replaced on schedule.
Span (span gas): The certified known-concentration gas used as the high point in calibration/bump testing; has an expiration date. See Core Concepts.
STEL (Short-Term Exposure Limit): The maximum average exposure over a short window (typically 15 min) that shouldn't be exceeded. See Core Concepts.
SNM (Special Nuclear Material): Fissile materials (e.g., certain uranium/plutonium) — a RIID/neutron category of highest concern.

T

T90 (response time): The time for a sensor to reach 90% of its final reading after a step change in gas. Move slower than your T90. See Core Concepts.
Time-distance-shielding: The three levers for reducing external radiation dose: less time, more distance (biggest effect), more shielding. See Radiation.
TIC (Toxic Industrial Chemical): Common industrial toxics (e.g., chlorine, ammonia, HF) that are hazards in their own right and detectable by EC sensors, tubes, and IMS TIC modes.
TLV (Threshold Limit Value): ACGIH's recommended exposure guideline (not legally enforceable), often more current than the PEL. TLV-TWA is the 8-hour average form. See Core Concepts.
TWA (Time-Weighted Average): An exposure averaged over a work period (typically 8 hours). See Core Concepts.

V

VOC (Volatile Organic Compound): A carbon-based chemical that readily evaporates into air — the broad target class for PIDs and FIDs.

W

Wheatstone bridge: The balanced circuit a catalytic bead uses to measure the temperature difference between its active and reference beads.

Z

Zero / zeroing: Setting an instrument's clean-air baseline. Must be done in genuinely fresh air or the instrument reads low thereafter. See Core Concepts.
Zero drift: Slow wandering of a sensor's baseline (zero point) over time due to aging, temperature, or contamination — corrected by calibration.

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