Public Lab Research note

This is an attempt to replicate an activity.

My DIY Formaldehyde test kit

by mathew | July 10, 2015 00:58 10 Jul 00:58 | #12045 | #12045

mathew was awarded the Basic Barnstar by warren for their work in this research note.

What I want to do

Compile under one note the parts, assembly, and calibration of my DIY formaldehyde test kit following @nshapiro's research on formaldehyde testing, my investigation of airflow (part 2) following ideas from from @davidmack, @gretchengehrke, @danbeavers, @nshapiro, and @warren and @nshapiro's work on photo cards, as well as some of my ideas on usability coming out of work on Lending Library Kits.

My attempt and results


  • 3/4" drill bit
  • 7/64" drill bit
  • hand drill
  • philips screwdriver


Total: $78

Substitutions: a #3 stopper with two 3/16" holes would be better for a soda bottle or other plastic bottle as a stand.


pump conversion

We're going to convert the pump to suck rather than blow by turning the valve around. remove the four philips screws on bottom of the pump then do this:


GIF by @nshapiro

reassemble! one side should now be a vacuum pump.

valve attachment & tube holder

cut a small length of 1/8" tubing, attach to the small black screw valve that comes with the pump, and attach another roughly 50cm length of tubing to the other end of the pump. Push the 50cm tube into one of the #2 bottle stopper's holes:


Tubes can now be pushed into the other stopper hole. I am partial to stoppers because they hold the tubes better than the tubing alone, and keep me from putting my fingers near the broken tips. This glass bottle also provides a stable base lifting the tip of the tube up to 35cm above whatever surface its placed on. I think this is a little easier than @warren's "smellosaur" setup.

tube tip breaker

Drill a 7/64" hole in the brass tube to make a tip breaker.


tips can be pre-scored to break in the appropriate location either with a heart-shaped scorer that comes with the tubes. alternately, if you're like me and lost it, you can etch a circle around the tube with a corundum nail file:

score.png tip.png broken_tip.png

graduated cylinder modification

drill a 3/8" hole in the bottom side of the graduated cylinder and screw the air barb in to cut threads into the plastic. Then screw it back out, wrap in teflon tape going right-wards so the tape doesn't bunch up when screwing the air barb back in.



There are two possible setups for calibration, attaching the graduated cylinder straight to the top of the formaldehyde tube, or using the bottle as a "dropout" to prevent bubbles from reaching the formaldehyde tube. This dropout setup is very likely better, and doesn't require one to watch the air line:


Notice in the dropout configuration the formaldehyde tube still needs its arrow pointed towards the pump, and has to be flipped upside down.


The calibration process is essentially: you wet down the walls of the graduated cylinder with bubble solution, and then dip the top in a tray of bubble solution to start a soap film, and then time its transit. We're shooting for 300ml/min (.3 Liters/m). Watch me calibrate:




In my case I didn't have the thermometer hygrometer I recommended, but i can use a thermometer in our space, and the humidity measurement from the weather report. Humidity is only an issue if it is below 5% or above 95%.

I set a 1/2 hour timer on my phone, filled out a test card, took a photo of the test card, ran the pump for 1/2 hour, and then corrected the reading for temperature using the temperature correction factor chart. Watch me run it:

Cards, before and after:

IMG_20150702_175234.jpg IMG_20150702_182614.jpg

I immediately emailed myself the two photos, whose built-in EXIF time stamps and e-mail time stamp record constitute proof I ran a 1/2 hour test and wasn't overloading the tube.



That's great work. The videos are very well done and have a lot of info explained in a nice, straight forward manor.

I like the photo card. Add a spot for the flow rate and always record the exact flow rate measured. I know you spent a lot of time nudging the pump to the exact flow but it's not practical to expect users to do that. In practice most users will get it "close enough" so it's important to always record the actual measured values. If the sample goes long or the flow is a little off you can correct for that in your calculations provided you have the actual measured times and flow recorded. Maybe a spreadsheet to crunch the numbers would be helpful too.

Also, if you have a fleet of equipment, it's good to put serial numbers on the equipment, like "Pump 10" and "Cylinder 2" then you record that on the card as well. It's good quality control because eventually something will falter and you want to be able to identify the defective device.

I would also encourage field notes and observations when deployed. What did the user see, smell, and hear? Maybe it was raining outside or the carpet was new. Did the place smell bad--what did it smell like?? If someone complaining about something then record their words verbatim.

Looking for some forms to use as a guide, I found the NIOSH Guide for Building Air Quality, see Take a look at page 185 (pdf page 190), "Occupant Interview" and page 223 (pdf page 222), "Hypothesis Form." Those might be a good start for field notes.

Also, I think taking three samples in the same location back-to-back is good practice. I know it drives up cost but it quickly reveals the precision of your methods.

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you are the boss. Awesome. I have some GCM field sampling notes, and those forms echo what David Mack just typed. Although i suppose weather isn't as big a factor in interior spaces?

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studio shots






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yes. yes yes yes yes.

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That is very fantastic from the design, the construct, the starting, the video, the images...Everyone said a new era of computer assisted drug design( is coming, but you made it by only hand and brain. Good job!

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