Formaldehyde Detectors Compared: RKI FP-31, FP-330 and Detector Tubes for Canada

A formaldehyde detector has to read well below 1 ppm, because the limits that matter sit between 0.016 and 0.3 ppm. ERE lists three ways to do it: the RKI FP-31 (colorimetric tablet, portable), the RKI FP-330 (colorimetric tape, mains-powered monitor with alarms) and Sensidyne formaldehyde detection tubes. This guide sets each one's published range and error band against the Canadian and occupational numbers, so you can see which can answer your question. All sit in the portable gas detectors range.

In this guide

• What Formaldehyde Levels Does a Detector Need to Resolve?
• Which Formaldehyde Detector Types Does ERE List?
• Can an FP-31 Reading Prove a Limit Is Met?
• When Do You Need Continuous Monitoring Instead of Spot Checks?
• How Do You Choose a Formaldehyde Detector, Step by Step?
• Frequently Asked Questions

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What Formaldehyde Levels Does a Detector Need to Resolve?

It needs to resolve roughly 0.02 to 0.3 ppm. Formaldehyde is a confirmed human carcinogen (ACGIH A1; IARC Group 1), and the published numbers cluster at the low end (CCOHS).

Benchmark	Level	Source
Residential long-term (8 h)	50 µg/m³ (40 ppb, 0.040 ppm)	Health Canada
Residential short-term (1 h)	123 µg/m³ (100 ppb, 0.100 ppm)	Health Canada
NIOSH REL (TWA / 15-min ceiling)	0.016 ppm / 0.1 ppm	CCOHS
ACGIH TLV (TWA / STEL)	0.1 ppm / 0.3 ppm	CCOHS

CCOHS notes that many, but not all, Canadian jurisdictions use limits similar to the ACGIH values, and that legislation varies. Confirm the limit that applies to your site before choosing a range.

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Which Formaldehyde Detector Types Does ERE List?

Three, built on the same colorimetric principle but packaged differently. Prices are quoted on request.

	RKI FP-31	RKI FP-330	Sensidyne tubes
Format	Portable, built-in pump, LCD	Portable-size monitor, 6.5 kg, digital ppm display	Glass tubes, hand pump (AP-20S), 10 per box
Principle	Photoelectric photometry on a colorimetric tablet	Photoelectric colorimetric tape	Length-of-stain colour change
Range on record	0 to 0.4 ppm (30 min); 0 to 1.0 ppm (15 min)	0.030 to 0.500, 0.05 to 1.00 and 0.3 to 5.00 ppm	171SC 0.05 to 4 ppm; 171SB 1 to 35 ppm (two tubes per test); 171SA 20 to 1,500 ppm
Result	One accumulated reading per 15 or 30 min sample; stores 99 readings	Continuous, tape-remaining display and end-of-tape alarm	One spot reading per sample
Alarms / output	None listed	Audible and visual alarms, alarm relays, 4-20 mA	None
Power	4 AA alkaline, about 12 h continuous	Mains (see note below)	None
Interferences	Maker states no known interfering gases	Maker states no response to hydrocarbons, alcohols, solvents, CO	Check the tube datasheet

Two points the records leave open. The FP-330 text says both "115 VAC powered" and a 100 to 220 VAC universal input, so confirm the supply before installing. And the FP-330 record gives no accuracy figure, so ask for the datasheet if you need one. Passive badges are a fourth route: the ChromAir badge record links a formaldehyde instruction sheet, but its listed exposure range and detection limit are series-level, so ask us for the formaldehyde-specific figures.

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Can an FP-31 Reading Prove a Limit Is Met?

Only for the higher limits. The FP-31 specification gives accuracy as ±20% of reading or ±5% of full scale, whichever is greater. At low readings the full-scale term wins, which sets a fixed error floor: 5% of 0.4 ppm is ±0.02 ppm, and 5% of 1.0 ppm is ±0.05 ppm. Applying that to the benchmarks (our arithmetic from the published spec, not a maker claim):

True level	30-min mode (0 to 0.4 ppm)	15-min mode (0 to 1.0 ppm)
0.040 ppm (Health Canada 8 h)	0.020 to 0.060 ppm	0 to 0.090 ppm
0.100 ppm (Health Canada 1 h, ACGIH TLV-TWA)	0.080 to 0.120 ppm	0.050 to 0.150 ppm
0.300 ppm (ACGIH STEL)	0.240 to 0.360 ppm	0.240 to 0.360 ppm

Three consequences. Use the 30-minute mode whenever the target is at or below 0.1 ppm, because its error band is 2.5x tighter. A 0.016 ppm NIOSH REL is smaller than the ±0.02 ppm floor, so the FP-31 cannot confirm it; that target needs a low-level sampling method with laboratory analysis. And the instrument returns an accumulated 15- or 30-minute value, not a peak, so it fits spot checks and area screening, not alarm duty. The sample window also means a reading is only as good as the conditions during that window: note ventilation state, temperature and what was running.

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When Do You Need Continuous Monitoring Instead of Spot Checks?

When the source is steady and people work near it. The FP-330 suits that case: replaceable tape cassette, a ppm display, audible and visual alarms, alarm relays and a 4-20 mA output you can send to a controller or logger. Its tape-saver mode extends tape life where background levels are high. The records list these applications for both RKI models:

• Furniture and woodworking and engineered wood products
• Coating, varnishing, painting and corrosion-resistant finishes
• Adhesives and carpet manufacture and storage
• Heat treatment operations and medical or veterinary settings
• Manufactured home, trailer and RV inspection

If the job is a one-off survey, the FP-31 or tubes cost less than a fixed monitor. If the job is a recurring process, a continuous unit with alarms removes the need to schedule spot checks. For a broader view of portable versus fixed instruments see the portable gas detector guide and the gas detection tubes guide.

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How Do You Choose a Formaldehyde Detector, Step by Step?

1. Write down the target. A residential guideline (0.040 or 0.100 ppm), an occupational limit (0.1 or 0.3 ppm) or a source-finding screen.
2. Check the error floor against the target. If the maker's error band is as large as the target, the tool cannot prove compliance.
3. Pick spot or continuous. Surveys suit the FP-31 or tubes; steady processes suit the FP-330.
4. Match the range. Tubes jump from 0.05 to 4 ppm to 20 to 1,500 ppm; pick the one that brackets your expected level.
5. Plan the consumables. The FP-31 uses detection tablets (20 per box), the FP-330 uses tape cassettes, tubes are single-use.
6. Plan service. Ask about calibration and rental when you request a quote; the FP-31 and FP-330 are marked service eligible. Our indoor air quality guide covers building-wide monitoring.

Tell us the target level and the setting and we will return a specific recommendation.

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Frequently Asked Questions

What range does a formaldehyde detector need?

Roughly 0.02 to 0.3 ppm. Health Canada's residential guidelines are 0.040 ppm over 8 hours and 0.100 ppm over 1 hour, and the ACGIH limits are 0.1 ppm (TWA) and 0.3 ppm (STEL).

How accurate is the RKI FP-31?

Its specification is ±20% of reading or ±5% of full scale, whichever is greater. That is a floor of ±0.02 ppm in the 0 to 0.4 ppm (30 minute) mode and ±0.05 ppm in the 0 to 1.0 ppm (15 minute) mode.

What is the difference between the FP-31 and the FP-330?

The FP-31 is a battery-powered portable that returns one accumulated reading per 15 or 30 minute sample. The FP-330 is a mains-powered tape monitor with a ppm display, alarms, relays and a 4-20 mA output for continuous monitoring.

Are detector tubes sensitive enough for formaldehyde?

For screening, yes. Sensidyne's most sensitive formaldehyde tube on ERE's record covers 0.05 to 4 ppm, which is above the 0.040 ppm residential 8-hour guideline, so tubes confirm higher levels rather than prove low ones.

Can ERE calibrate or rent formaldehyde detectors?

ERE's records mark the FP-31 and FP-330 as service eligible. Ask about calibration and rental availability when you request a quote.

Related articles

• Portable Gas Detectors Buyer's Guide for Canada
• Gas Detection Tubes: A Buyer's Guide for Canada
• Indoor Air Quality Monitoring for Commercial Buildings

Lire en français : Détecteurs de formaldéhyde : FP-31, FP-330 et tubes détecteurs comparés pour le Canada