This article will cover how to choose the correct filter cartridge to protect you against oxalic acid when treating your beehives for varroa mites.

I've seen a lot of articles and forum posts asking which 3M cartridge is the right one to use for protection against sublimated Oxalic Acid. The problem is I've also seen a lot of wrong answers. So let's delve into this topic and figure out the best protection for you to use when sublimating Oxalic Acid to treat for Varroa Mites in your beehives.

Why Is This Article Important?

Oxalic Acid is the best choice currently for the control of Varroa Destructor (varroa mites). It has been shown in long terms studies that varroa mites cannot develop a resistance to this method of elimination. It causes much less absconding than other treatments and is more effective as a miticide than nearly all other treatments. Treatments like Apivar and others are all causing mites to develop immunity to these treatments and they are so harsh that they cause hives to abscond on a regular basis. So if Oxalic Acid is the best choice, we should know how to use it safely.

Sublimation vs. Vaporization

We need to be correct in our assumption of what exactly we are doing when we heat Oxalic Acid. If we do not know, it is easy to choose the wrong 3M cartridge. Choosing the wrong cartridge to protect against Oxalic Acid when treating for Varroa Mites is exactly what we do not want to do, to prevent injury to ourselves.

Vaporization is a transitional phase of matter in which a solid first change to a liquid and then changes to a gas.

Sublimation, on the other hand, is the direct change from a solid to a gas.

Sublimation is what we are doing when we use Oxalic Acid crystals and a "vaporizer". Honestly, to be accurate, these units should be called "sublimators" I guess, lol.

Organic Vapor vs. Organic Acid

Getting this part right is where I see most of the mistakes on the forums and in the advice I see given online arise from. The problem comes in when people who do not know the definition of "Organic Vapor" attempt to advise others that a cartridge for organic vapor will protect them from an "Organic Acid" like Oxalic Acid. This simply isn't true.

An "Organic Vapor" is typically defined as the evaporated products of Organic Compounds. So what is an organic compound? Most people would guess that organic compounds are made from living things. While this is in a way correct, it is not 100% correct. Organic compounds are any number of chemicals and compounds that contain carbon. Carbon is the basic building block of life as we know it. Most organic compounds are produced from petroleum, which used to be alive and contains carbon molecules. This includes things like gasoline, paint thinners, diesel fuel, turpentine, most plastics,  acetone among many others.

An "organic vapor" usually refers to the gas given off by the rapid evaporation of these carbon-based compounds, none of which I listed would be considered an "organic acid", which is really what we need a cartridge to protect us from, as Oxalic Acid is an "organic acid" and not an "organic vapor". To be even more accurate, when we use Oxalic Acid the way we do in our beehives, it is actually a "sublimated organic acid".

What Is Oxalic Acid?

Oxalic Acid is a strong alpha, omega-dicarboxylic acid that is ethane. It is also known as ethanedioic acid. It has a  molecular structure of C2H2O2. Two carbon atoms (makes it organic), 2 Hydrogen and 2 Oxygen atoms. It occurs naturally in many plants and vegetables, so we can say it is harmless at correct dosages. It is not metabolized by the body but excreted in our urine. So if you are exposed, and you often are by eating vegetables, it passes harmlessly out of your urinary system.

Oxalic Acid is a "strong acid" and has a ph of 1.3 (water has a ph of 7). The ph scale goes from 0 to 14. This explains why water has a ph of 7, it is neither an acid nor a base. However, we can see that a ph of 1.3 Oxalic Acid is a very strong acid, almost as strong as acid can be. This is why we must take great care in selecting the correct 3M cartridge filter, as oxalic acid can and will destroy your lung tissue if inhaled.

Which 3M Cartridge Is The Correct 3M Cartridge?

3M manufactures a wide range of cartridges, particle filters, and combination filters. These many filters are all designed to do specific things and protect from very specific vapors, compounds, particles, etc.

3M Particulate Filters:

particulate filters

These filter out only aerosols like dust, mists, fumes, smoke, crystals (of OA), mold, bacteria, etc. Some of these particulate filters can filter out "nuisance-level" gasses and vapors. In other words very small amounts. You need a particulate pre-filter since some of the sublimated oxalic acid will recrystallize in the air around you. This means it is no longer a "gas" or a "vapor" but a "particle" and needs a particulate pre-filter.

3M Gas & Vapor Cartridges:

gas vapor cartridges

These filter out only gasses and vapors. There are different cartridges for different kinds of gasses and vapors. You need one of these in conjunction with the particulate filter above to be most effective.

 3M Combination Cartridge/Filters:

combination cartridges

These filter out particles, gasses and vapors. Different combination cartridge/filters are used depending on the gas or vapor present. This is the product that combines both of the above particle filters and a cartridge into a single unit which will get out the Oxalic Acid no matter what form it is in.

So Which Do I Use?

 To decide which is the best choice or combination of choices, we need to consult the 3M manufacturer's specifications for each cartridge and filter. Then apply what we know to our selection. Below is the 3M published list of color codes for their cartridges and filters.

3M color code chart

We are using an "Organic Acid". From the chart, we can see that black cartridges cover organic vapors and that white cartridges cover acid gasses. But we have both an organic and an acid. So we see that 3M has a cartridge to cover this. It is the yellow color-coded cartridges. The 6003 series. There are a lot of cartridges in this series though, which one do we need for Oxalic Acid? We need one with a P100 prefilter and an OV/AG cartridge.

From 3M's product line we have two choices. Either the 60923 cartridges or the 60926 cartridges. As we can see from 3M's chart, these are the only two cartridges which will fulfill our needs.

 60923 60926 cartridge

So based on this, I would select either of these two cartridges to go into my respirator. These cartridges are disposable and reusable. This one pictured below is the 60923 and is a pink and yellow combination particle filter, organic vapor filter and organic acid filter. These cartridges for oxalic acid can be ordered here.

It looks like this:

60923 cartridge

Now that we have figured out exactly which cartridge you need to protect you, let's discuss respirators.

Which Respirator Should I Choose?

3M recommends when working with organic acids that a full face respirator is used. This provides the most protection for your eyes. Most people opt for the half mask though as it is far more comfortable. I will leave it up to you to decide between a full face or a half mask. I personally use the recommended full face mask for working with these acids.

All you need to make sure of is that you choose a mask with replaceable cartridges, as 3M makes many masks that come with permanent cartridges which cannot be replaced. Ask your local big box store for assistance with selecting one with replaceable cartridges if you are not sure.

Here is an example of a full face mask: You can order one here

full mask

 Here is an example of a half face mask:

half mask

Our full line of products to control varroa mites is located here


I am using publicly available information from 3M to reach the conclusions in this article. Those conclusions may be incorrect due to errors in the published data from 3M. I have made every effort to research multiple sources to verify any data given here. I am also using any media and copy in this article owned by 3M in an educational attribution.