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After applying sanitizers can they catch fire, if yes, then after what time is it safe to use the hands, say in the kitchen. Also one more question is that if they are flammable then the flammable component is alcohol. However as soon as we apply the sanitizer the alcohol evaporates? Then how can they remain flammable on our hands?

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    $\begingroup$ As soon as alcohol evaporates, they cease to be flammable. Soon as it is, this does not happen instantly, though. $\endgroup$ – Ivan Neretin Jun 11 at 5:13
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    $\begingroup$ Hm, their medical application Is off-topic, but their physical and chemical properties are still on-topic. $\endgroup$ – Poutnik Jun 11 at 5:39
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    $\begingroup$ @Poutnik It's still the same bag. Being too broad, this should be already closed. $\endgroup$ – Mithoron Jun 11 at 19:18
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Firstly, we should realise that sanitizers should not be considered as pure alcohols, alcohols are indeed a major component of it but many other important components are also present. A typical sanitizer contains these things -

Isopropyl alcohol/ Ethyl alcohol, Glycerin, Water, Carbomer(stabilizer) and some other components mostly related to cosmetics.

Now, i will answer your questions one by one

After applying sanitizers, can they catch fire?

Yes, there is 60%-70% alcohol content which is highly flammable. Organic compounds like alcohols, alkanes etc have very high enthalpy of combustion ($\Delta_\mathrm{c}H^\circ$ = -2000 kJ/mol for Isopropyl alcohol) and they can evaporate very easily due to the heat of our hands($\Delta_\mathrm{vap}H^\circ$= 40kJ/mol for isopropyl alcohol).

As soon as we apply alcohol, it evaporates so why is it still flammable?

This is actually wrong, as I earlier mentioned, that sanitizers are not only alcohols, in fact, the 'carbomer' present acts as a stabilizer to emulsify/dissolving all the components in it. These stabilizers prevent the alcohol to evaporate immediately and allow it to disinfect our hands fully. Also, after applying sanitizers, many of you might feel hands becoming sticky it is because of the presence of Glycerin and other cosmetic products used in it which act like a moisturizer. So generally it takes about 30-40 seconds for all(mostly) the alcohol to evaporate and sustaining a risk to be inflammable for a long time. A thing to keep in mind is that the residue (mostly Glycerin) is also flammable(not that much, it's flammability rating is one) so after the alcohol has evaporated, you aren't fully safe from catching fire.

If your are working in kitchen, there is no actual need of using sanitizers as you can always wash hands in sink with soap and water.

I hope this answer cleared some of your doubts, stay safe :).

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    $\begingroup$ In this answer, I don't think I have added something which needs a reference, the enthalpy data is the standard NIST data, and everything else is rather applications of organic chemistry, carbomer being a stabilizer due to it's high molecular mass etc. $\endgroup$ – Pj30 Jun 11 at 7:09
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    $\begingroup$ Water is also a common ingredient in hand sanitizer. $\endgroup$ – SE - stop firing the good guys Jun 11 at 13:28
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    $\begingroup$ @SE-stopfiringthegoodguys thank you for the comment, yes, water is also a common ingredient in sanitizers. I have updated my answer. $\endgroup$ – Pj30 Jun 11 at 13:43
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    $\begingroup$ @piojo thank you for your comment. Comment part 1 You are absolutely right, carbomer(or some other chemicals) can be formally called as a thickener but if you compare the time taken for alcohol to evaporate of the sanitizers you will see a drastic difference,. the WHO sanitizer evaporates way to fast, but note that it does not decrease it's potential to sanitize (notice the volume you take of your WHO sanitizer and compare it with the branded sanitizer). $\endgroup$ – Pj30 Jun 11 at 16:11
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    $\begingroup$ @piojo Comment part 2 Using a thickener/solvent just makes it more efficient as most of the alcohol is used up after sanitizing hence it works with very small amounts, while the WHO sanitizer which is somewhat thinner is used in comparatively a bit more amounts at a time works just the same. (The comment was exceeding the word limit so had to answer it in 2 parts ;-)) $\endgroup$ – Pj30 Jun 11 at 16:12

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