These formaldehyde testing kits are one part of our multi-pronged Indoor Air quality monitoring efforts.
Follow active development on the tag 'formaldehyde.'
Our goal is to measure formaldehyde at typical environmental exposure levels found in homes and workspaces that are irritating and potentially carcinogenic over the long-term, a range from 8-600 parts per billion (ppb) or 0.008 - 0.6 parts per million (ppm), but usually below 150ppb. Read more in Formaldehyde Exposure.
We are also interested in short measurement periods, i.e. an hour or less, so that environmental factors such as ventilation, or the operation of a formaldehyde-generating process or appliance can be correlated.
We would like to produce data comparable between sites and control for false positives (other gasses detected by the method). Being able to calibrate the sensors consistently and inexpensively is therefore critical.
Inexpensive electronic monitors are usually not very in the .008-.1ppm range most likely to be found in homes, can be difficult to keep in calibration, and often respond to other gasses as well. A review of current electronic sensing techniques is available through the NIH.
We've focused on chemical-reaction-based testing as better documented systems. The two most common methods for detecting formaldehyde in the home involve passive collection of the chemical via a badge (8 to 48 hour test time). These methods require samples to be sent back to the lab for analysis. The send-it-to-the-lab model introduces three problems:
- expensive high pressure liquid chromatography is required at the lab (HPLC, which cost ~$30,000).
- the possibility of contamination during transportation and analysis.
- the cost of testing the transportation process for contamination.
In order to ensure the accuracy of a send-it-to-the-lab test you need to purchase two additional tests, known as a “field blank” and a “trip blank,” to ensure that your sample wasn’t contaminated.
- Three active sorbent samples with Home Air Check costs $217.50.
- Three passive badges with ACS costs $123.
not exactly low cost...
An alternative to these passive systems is to actively pump air through a sorbent material (30 minutes to 8 hours) that traps formaldehyde. Pumps can be very expensive, from $500-$3000, but the single-use sorbent materials can be inexpensive. @Nshapiro noticed one such published methodology and set out to replicate it.
Formaldehyde concentrations in household air of asthma patients determined using colorimetric detector tubes Karen C. Dannemiller et. al, Indoor Air. 2013 Aug; 23(4): 285–294. Dannemiller et al. replaced expensive pumps with calibrated 100-gallon aquarium pumps and used Kitagawa 710 formaldehyde detection tubes, which have a detection range of 10ppb-480ppb with +/-10% accuracy, and a test period of 30 minutes, making them close to meeting our ideal testing range.
The kitagawa tubes cost $7 each in quantity, and the Tetra brand Whisper 100-gallon aquarium pump costs between $25-$55 depending on the retailer.
from published method to a DIY test
Dannemiller et al. have access to a professional lab to calibrate their equipment, and their written chain of custody (where everyone who handles a sample signs a piece of paper) is taken on trust because they're academics. A DIY test will be conducted without access to lab equipment and without the implicit trust of a credentialed scientist. We will have to create new systems for both.
In order to convert the published methodology of an aquarium pump and kitagawa 710 formaldehyde tube into a fully usable kit we need a minimum of:
- a method of pump calibration
- a means of data recording and verification
...but it would also be useful to have:
- a means of easily attaching the Kitagawa tubes to the pump
- a timer and automatic shutoff to guarantee proper pumping time
how good is good enough?
How precisely do we have to measure and control the flow of the pump, and how often do we have to take a measurement of the pump? Do we have to measure the flow through each different Kitagawa tube, or can we use the same used reference tube and then run multiple tests without re-calibrating? Does the pump have a "warm up" period or is the flow consistent from startup and throughout operation?
Dannemiller et al.:
Pump performance was also validated by measuring the flow rate through the permeation tubes from four different pumps and from the same pump over time. The pump flow rate remained constant over the time period required for sampling. In addition, the slight variations in measured pump flow rate (262–350 mL/min) on different sampling dates in the field did not significantly affect the value of formaldehyde readings after sampling time correction to maintain a constant sampling volume (p=0.687).
Its nice to know that data can be corrected after collection for +/-20% variations in flow, but this statement is a little confusing to unpack-- are the slight variations in measured pump flow rate different from pump-to-pump, or variations in the same pump with the same calibration and the same Kitagawa 710 tube, or variations in flow between different tubes attached to the same pump? In @mathew's testing he hasn't seen significant day-to-day fluctuations from the same pump hooked up to the same Kitagawa tube, but did see variations in flow of +/- 10% between different tubes.
Dannemiller et al. failed to mention the actual means of calibrating pump flow rate on the sampling dates. What calibration method was used, how precise was it, and was each formaldehyde tube tested for flow or was the same standard tube used for calibration each time? Based on conversations between @nshapiro and the authors, we know that they used a NIST-traceable Mini-buck calibrator to calibrate pumps in the morning before the testing using the same standard reference tube and that the "time period required for sampling" over which they remained constant was a day, including travel between homes. At $1000 the MiniBuck is clearly not a DIY option, but it does measure flow at +/- 1%.
Dannemiller et al. also describe the timing of the tests as 'nominal' 30 minutes. Assuming that is +/-1%, or 30 seconds, then the authors measured flow rate was subject to +/-2% variation without accounting for flow variation between the different Kitagawa tubes. Trusting Dannemiller et al.'s results, we can effectively ignore the tube-to-tube variation and focus on the pumps' calibration and change over time. We're left with two questions:
- Can we measure flow accurately enough to limit flow rate variation to the +/-2% Dannemiller et al. had?
- How long do pumps hold their calibration?
suggested by @donblair
Calibrating for temperature and humidity
data recording & verification
Verification with network timestamps
In discussions between @warren @nshapiro and @mathew it was decided to try to collect information onto a card that could be photographed along with the test strip for a record. As well as collecting the information all in one place, the photograph, especially when taken with cell phone camera, can be used to make a traceable record of the test. By photographing the test setup before and after and sending that photograph through either the cell network or the internet, the communications containing the photograph will be time-verified by the network, providing 3rd party verification that the test period was within the time period that the test taker claims.
What information to collect?
- Date of test
- Test start time (We will probably want start times to be the same-ish, between 1:30pm and 3pm with a preference of 2pm)
- Test end time
- Tube serial number
- Read out on tube (PPM)
- Zip code
- Temperature (F)
- Humidity (can't perform test if under 10 or over 90)
- Housing Type: Manufactured, New (less than 5.5 years), Passive Green, Other _____
- My exterior windows and doors have been closed for 24 hours (this is for homogeneity control, easier than having them document each open window/door which would be the other option) (yes/no check box)
- My HVAC system has been blowing air ___% of the time during this test
C * Other observations (much blank space)
Complete DIY Kit + parts list
Lending kit + production files