Measurement Tools Suite

Correction Factor (CF) / Response Factor (RF) — PIDs are calibrated to isobutylene (CF = 1.0). To obtain the true concentration of another compound:
True concentration = PID reading × CF. CF > 1 means the instrument underreads; CF < 1 means it overreads. NR = no response (compound ionisation energy exceeds lamp energy).

Search for a compound above to view correction factors across manufacturers.

Enter the compound, lamp energy, and PID reading to calculate the true concentration. Select the manufacturer whose CF values you want to apply.

Compound

Manufacturer / Instrument

Correction Factor (CF)

PID Reading

Unit

Compound	CAS	IE (eV)	RAE 10.6	RAE 9.8	RAE 11.7	MX6 10.6	IGD 10.6	Drg HC	Drg LC

How PIDs work

A photoionization detector (PID) ionises gas molecules using UV light and measures the resulting ion current. PIDs are calibrated to isobutylene (2-methylpropene, CAS 115-11-7), assigned a CF of 1.00. Because different compounds ionise with different efficiency under the same lamp, a correction factor is required to convert the displayed reading to the true concentration.

Correction Factor (CF) = Response Factor (RF) — The terms are used interchangeably across manufacturers. RAE Systems uses CF; MSA, Industrial Scientific, and Dräger use RF. The calculation is identical: True concentration = PID reading × CF.

NR (No Response) — The compound's ionisation energy (IE) exceeds the lamp photon energy. The compound cannot be detected with that lamp.

Lamp energies: The most common PID lamp is 10.6 eV. High-sensitivity lamps at 11.7 eV can detect compounds with higher IE (e.g. some halogenated solvents), but degrade faster and are humidity-sensitive. Low-energy 9.8 eV lamps reduce sensitivity to common interferences.

Dräger sensor variants: The PID HC (high concentration) is suited to ppm-range work; the PID LC ppb version has a smaller measurement cell for sub-ppm detection. RF values differ between the two.

Manufacturer	Instrument	Lamp (eV)	Source	Compounds
RAE Systems	MiniRAE, ppbRAE, MultiRAE	9.8 / 10.6 / 11.7	TN-106	262
Industrial Scientific	MX6 iBrid	10.6	PID Response Factors table	115
IGD / GenSenova	SL-031	10.6	CF table SL-031-2	141
Dräger	X-am 8000	10.6	Substance list (PID HC + LC ppb)	90
MSA	ALTAIR 5X	10.6	Compound library (RF device-stored)	118 (no published RF)

CF values are sourced directly from manufacturer technical documentation. Values are for informational purposes only; always verify against the current manufacturer datasheet for your specific instrument and lamp. Humidity, temperature, lamp age, and calibration gas concentration all affect accuracy. This tool does not replace site-specific calibration procedures.

ISO GUM approach — occupational exposure measurement

Enter the uncertainty components for your measurement. Each component is expressed as a relative standard uncertainty (%). The combined standard uncertainty u_c is calculated by root-sum-of-squares (RSS). The expanded uncertainty U (k=2, ~95% confidence) is used for OEL comparison. Inputs follow EN 482:2021 / EN 13936:2014 framework.

Measurement result

Measured TWA concentration

Occupational Exposure Limit (OEL)

Units

Coverage factor k

Uncertainty components (relative standard uncertainty, %)

Sampling efficiency u_s (%)Pump volume calibration + sampler collection efficiency. Typical: 5–12%

Analytical method u_a (%)Extraction efficiency + instrument precision. Typical: 3–8%

Calibration / volume u_v (%)Flow rate calibration uncertainty. Typical: 2–5%

Workplace variability u_w (%)Day-to-day and between-worker variability. Enter 0 to exclude.

Additional components u_x (%)Temperature, humidity, substrate, blank corrections.

Preset method profile

Component	u (%)	u² (%²)	Contribution
Enter components above to build the uncertainty budget.

Typical uncertainty values for occupational sampling methods

Values below represent typical combined standard uncertainties for published NIOSH/OSHA methods under controlled conditions. Actual values should be taken from method validation data or laboratory accreditation certificates. Workplace variability is excluded from these figures.

Method reference uncertainty values

Method / analyte	Sampling u_s	Analytical u_a	Volume u_v	Combined u_c (without variability)
NIOSH 1500 — Hydrocarbons (GC-FID)	5%	3.5%	3%	~7%
NIOSH 2010 — Ketones (GC-FID)	6%	4%	3%	~8%
NIOSH 2531 — Formaldehyde (HPLC)	8%	5%	3%	~10%
NIOSH 5000 — Inorganic dust, gravimetric	7%	2%	4%	~8%
NIOSH 7400 — Asbestos fibres (PCM)	10%	20%	3%	~22%
NIOSH 9000 — Endotoxin (LAL assay)	15%	25%	5%	~30%
OSHA 7 — Mercury vapour (AAS)	5%	5%	3%	~8%
IOM inhalable dust — gravimetric	9%	2%	4%	~10%
GSP respirable cyclone — gravimetric	8%	2%	4%	~9%
Direct-reading instruments (calibrated)	10–25%	—	—	10–25%

EN 13936 / EN 689 compliance decision rules

Condition	Decision	Required action
C + U ≤ OEL	Compliant	No immediate action; maintain monitoring programme
C − U ≤ OEL < C + U	Inconclusive — further sampling required	Collect additional samples; consider 8-sample strategy per EN 689:2018 Annex G
C − U > OEL	Non-compliant	Implement controls; re-measure after controls to verify compliance

References: ISO/IEC Guide 98-3:2008 (GUM); EN 482:2021; EN 689:2018; EN 13936:2014. NIOSH manual: www.cdc.gov/niosh/nmam/