TOPIC:

JD: Yes, we are misunderstanding here. The flammability limit in volume % stands for the gas phase above the CD solution.

Henry's law says:

At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.

Or, the higher is the concentration of liquid solution of a gas the higher is it's concentration in the gas phase (in equilibrium).
There are concentrations of chlorine dioxide in gas phase (last column) for different concentrations of CDS (first column) in my table. Two examples (for 25 °C) are in the picture here:


From Occupational Safety and Health Guideline for Chlorine Dioxide

Reactivity

1. Conditions contributing to instability: Chlorine dioxide is a very unstable material even at room temperatures and will explode on impact, when exposed to sparks or sunlight, or when heated rapidly to degrees C (212 degrees F). Airborne concentrations greater than 10 percent may explode.
2. Incompatibilities: Contact with the following materials may cause fires and explosions: carbon monoxide, dust, fluoroamines, fluoride, hydrocarbons (e.g., butadiene, ethane, ethylene, methane, propane), hydrogen, mercury, non-metals (phosphorus, sulfur), phosphorus pentachloride-chlorine mixture, platinum, or potassium hydroxide. Chlorine dioxide reacts with water or steam to form toxic and corrosive fumes of hydrochloric acid.
3. Hazardous decomposition products: Toxic and corrosive gases and vapors such as chlorine gas or the oxides of chlorine may be released when chlorine dioxide decomposes.

Charlotte said:

Not completely understanding the info & charts in the PDF file, but it seems that concentrations up to 60,000 ppm could safely be made if the CDS is always kept cold. Is that correct?

No, relatively safe are concentrations up to 6000 ppm only. Keeping CDS cold is beneficial, but most important is to save it from (intensive) light, sparks (electrostatic charge) and similar.

Charlotte said:

And it seems that CDS concentrations no higher than 3000 ppm should be made using the shot glass method as that method is usually done at room temperature.

Yes, glass shot method is very simple and it's great advantage is that it is done at room temperature. But local concentration of chlorine dioxide might exceed the 10% flammability/detonation limit in the air space in the vessel above solution level. Again sharp light and so on is the main danger. I recommend to wrap the vessel into black paper or place it in a box as soon as possible after activation of MMS (and minimize the volume of CDS to be prepared). At least goggles should be mandatory to protect eyes in case of accident.
I prefer (as Steve wrote in this topic) the forced air method. It guarantees that CD concentration in gas phase is very low during the whole production process. Flowing air stirs the reaction mixture, too. This method is used e.g. in analytical laboratories for preparation of ClO₂ standards (details see in attachment).

Charlotte: To be honest I don't know what exactly authors of the method meant by the words "critical level" of volume. But I am 100 % sure nothing in the paragraph you quoted is important for us (CDS users). Analysts have to know exact concentration of CDS and it is obvious that after some withdrawals the concentration goes little down, that’s all.

The important things in the pdf file from the point of safety are: usage of forced air (diluting of CD concentration, stirring of reaction mixture), low concentrations of chlorite and acid solutions, gradual introduction of the acid to the chlorite, no heating.

Kelly C’s account is cautionary.

Interesting for me is usage of aspirator bottle with water. I speculate that wet air more easily absorbs chlorine dioxide from reaction mixture and then the CD retains more efficiently in the receiving water.

Charlotte: I don't think the ClO₂ loss in the air space is significant. Let's make simple calculation. Let's consider very small amount of 3000 ppm CDS in 1 liter bottle, so that there is free volume 1 liter of air saturated with CD. Content of the CD (from the table in my pdf) is 4.6 % (volume %) so it's volume is 0.046 liter. There is a rule that one mole of a gas has volume approximately 22,4 liter at normal temperature and pressure. Molecular weight of CD is 67.45 grams. So the mass of 0.046 liter is 0.046x67.45/22.4 = 0.14 g. One liter of 3000 ppm CDS has 3 grams of CD. The loss of CD is about 4.7.%. Of course the overall loss will be greater a lot as some CD escapes from the bottle, but to my mind it is still negligible. There is much more uncertainty at measuring concentration with strips. The calculation is valid for 25 °C. For CDS stored in fridge the loss will be a little bit less. This percentage loss doesn't depend on volume of the bottles or its number.

But from the point of safety the situation is completely different, especially for strong CDS solutions. Let's compare e.g. 1 liter bottle full of CDS with the same amount divided in ten small bottles. There will be 1 liter of air saturated with CD or 0.1 liter* respectively at the end. In the case of an accident the consequences will be quite different – in the blast intensity and the amount of chlorine dioxide gas that is released to atmosphere from the liquid.
* I suppose that every 100 ml bottle will be rinsed with water when it is empty.

So interesting. I had a bottle of 12500ppm CDS in my fridge for some time (over 6 months). It was in a 4 oz PET bottle, and by the time I used it, it had off-gassed somewhat, but was still quite dark, and about 2 oz. Never had a problem with it. Of course, I recognize that I did not do the math, nor, when I ultimately incorporated it into my "mix" of all the various bottles of CDS I had in my fridge, did I test it to see what the ppm actually was. Was the fact that I kept it in the refrigerator all that time significant in this regard?

I realized that Henry's constant and ClO₂ partial pressure are heavily temperature dependent and I made same estimation for lower temperature. If the solution is kept at 5 °C (at fridge), the partial pressure and volume content of ClO₂ in air in the bottle are lower (about one half of these at 25 °C). Consequence is that the critical amount 10 % (v/v) in the air is not overstepped up to CDS concentration circa 13000 ppm. So, there is a good reason to store CDS in fridge, especially the high concentrated one.
Due to lower partial pressure at 5 °C the speed of gas off is also slower - another beneficial of keepinh CDS solution cold.