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Name: Gary
Status: other
Grade:
Country: USA
Date: Spring 2010


Question:
Can petroleum jelly on someone's face such as lips, nose or ears and oxygen from a low pressure devise such as a concentrator or O2 bottle cause a flame?



Replies:
Hi Gary -

I think Petroleum jelly will be more dangerous in the presence of pure oxygen.

Immersed in one atmosphere of pure oxygen, at all times, the density of oxygen dissolved in the jelly will be a little more than the density of the oxygen in the air around it. That would still be at least 100 times less dense than the substance itself, i.e., the jelly can absorb 0.1%-1% of its mass in oxygen. (The same thing is true of a thin layer of pure water, I think. But water is not burnable.) So it is not pure rocket-fuel waiting to go off, but it is noticeably closer to a dangerous mix.

Flammable substances burn much faster and hotter in flowing pure oxygen, and with some oxygen dissolved within they ignite much easier.

I would not at all expect this mix to ignite spontaneously, but it would ignite more easily than jelly in normal air. A static spark will not usually ignite jelly in air, but it might well ignite jelly in oxygen. Then for as long as the oxygen continues to flow over the jelly, the burning will be considerably more intense than burning in normal air would be.

This could be a serious safety issue.

I think that what normally defends against ignition of petroleum jelly is that it has a high density of dissolved solvents that can boil off at less than ignition temperature, cooling the jelly's outer surface whenever a heat-source attacks it, keeping that spot cooler than the ignition temperature.

Also helps that it is spread in a thin layer, so that:

a) the evaporation-cooled surface is very close

b) the water-based, conduction-cooled skin beneath it is very close.

Both make it hard to get any of the thin layer up to ignition temperature, if it is spread very thin.

Furthermore, if the layer is very thin, the maximum total damage that can be done if it does all burn away is not much compared with the thermal mass of the skin beneath it. A thin layer probably cannot make a deep burn.

So I would be sure to spread it quite thin, not leave any thick globs or palpably thick layers, if using oxygen. And spread only on the skin. If on clothes, the cloth provides no heat-sinking beneath the jelly to prevent ignition. The porosity or fluffiness of the cloth means that any jelly on it will probably cannot be spread thin. And once ignited, the clothes themselves are sufficient fuel to continue to burn, unlike skin with its high water content. So I would only put it on skin.

Are you using it for the menthol vapors and decongesting effect, as people with colds do, or for skin-protecting effects? If for skin-protection, there might be a different skin lotion or cream you could change to. Most lotions or creams are water-based mixes, considerably less flammable.

I think concentrators do not provide 100% oxygen, rather more like 40%, up from the usual 20% that is in normal air. I tend to think bottled 100% oxygen would produce considerably more increase in risk than a concentrator. I can imagine that if buying bottles, 100% is far more economical than 50%, so one would tend to buy 100%. In such cases it would be nice to have a small machine that mixed the 100% bottle's output with a similar volume of normal air before it gets into the plastic tube that goes to the patient. I don't know if such a machine is available or how much it would cost to produce. However it seems to me that it might not be too difficult.

I am not quite sure how to quantify the increased risk experimentally. A properly designed experiment would compare ignitability in at least three concentrations of oxygen, such as 20% (air), 50%(or concentrator max.), and 100% (bottle), and value found at 20% would reflect the normally-not-very-high level risk implied by long experience with petroleum jelly in normal air. Certainly static sparks up to at least 15 kiloVolts from [100 pico-Farads + 1000 ohms] (a "human-body-model") should be tried. The 15kV is big but the 100pF is small, so this is a typical-sized static zap. And it is charged through a resistor of at least 100 meg-Ohms so the high-voltage supply can charge the capacitor but cannot add to the spark.

Jim Swenson



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