At which pH does your skin burn?

[katchum]

I searched up NaOH and saw that it's irritating at 0,05 to 0,5 mol/l. So I guess at a pH of 12,7 you will burn your skin. Is that true?

I'm going to do an experiment with 5% NaOH. I thought it was a very small concentration but actually you could burn quite a bit with this solution after a little calculation.

 

[Borek]

It all depends on the several factors. Time, temperature and concentration being those most important.

Besides - what does 'burn' mean? Is it defined precisely enough?

 

[turbo]

Borek has a good point. Acids are fairly "honest" chemicals, in that they usually cause physical discomfort if they are strong enough to injure your skin. Caustics, on the other hand, can cause damage without much initial discomfort, and are notoriously hard to wash off the skin. So if "burn" means "causes physiological damage", that is different than if "burn" means "causes physical discomfort".

 

[berkeman]

I searched up NaOH and saw that it's irritating at 0,05 to 0,5 mol/l. So I guess at a pH of 12,7 you will burn your skin. Is that true?

I'm going to do an experiment with 5% NaOH. I thought it was a very small concentration but actually you could burn quite a bit with this solution after a little calculation.

What do you mean by do an experiment? Sounds ominous...

 

[katchum]

Let's say:

20 °C, 3 minutes exposure (then washed with water), physiological damage (skin can be scraped off or hurts when you touch it or is completely red).

Which pH will do this?


The test is:

We want to spray 2% NaOH with a spray nozzle up to 3 meters far into a pipe to mix it with some powder that is coming from a reactor. We need to neutralize this acidic powder. There is an airflow of 40 m/sec in a 300 mm pipe diameter and 15 m long. The powder comes in perpendicular to the pipe at 1300 kg/hour.

Just want to implement safety precautions.

 

[chemisttree]

Consider anything over pH 10 to be a caustic hazard. What concentration of NaOH will produce this pH?

If you are in the US, you should know that OSHA is not a small town in Wisconsin...

Although the standards discussed above do not define these terms, OSHA's Hazard Communication Standard is instructive. The standard at 29 CFR 1910.1200, Appendix A, defines a corrosive as:

A chemical that causes visible destruction of, or irreversible alterations in, living tissue by chemical action at the site of contact. For example, a chemical is considered to be corrosive if, when tested on the intact skin of albino rabbits by the method described by the U.S. Department of Transportation in appendix A to 49 CFR part 173, it destroys or changes irreversibly the structure of the tissue at the site of contact following an exposure period of four hours. This term shall not refer to action on inanimate surfaces.
Generally speaking, corrosive materials have a very low pH (acids) or a very high pH (bases). Strong bases are usually more corrosive than acids. Examples of corrosive materials are sodium hydroxide (lye) and sulfuric acid.

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=27181

Let us know how the rabbits do.


AND... don't tell anyone you get your advice from an online bulletin board. You might want to consider consulting a http://www.abih.org/general/cihcaih.html" .

 

[Woody101]

A few years back when I was involved in Hazardous Material Emergency Response, we were taught that anything with a pH below 2.5 or above 12.5 was corrosive to skin. I have looked through some of my old reference material but I can't find anything to verify that. Perhaps you could give your local Fire Dept Hazmat Team a call. They should know.

 

[croghan27]

Borek has a good point. Caustics, on the other hand, can cause damage without much initial discomfort, and are notoriously hard to wash off the skin. So if "burn" means "causes physiological damage", that is different than if "burn" means "causes physical discomfort".

Working in an oil refinery's hydrogen plant I had to charge the 'benfield system' with sodium bicarbonate. The tank was in a confined area. Outside (this was northern Canada) it was -45 so I was wearing heavy clothing. Naturally I began to perspire - perspire in the dust of the bags of sodium bicarbonate (Hooker Chemical Co.) I was adding to the mix.

When the task was completed I went about some other duties, outside. After about 45 minutes I came back to the kitchen/rest area and my workmates began to yell at me ... "Wash your face! Wash your face!"
The bicarbonate and my perspiration has united to form NAOH and that had burned off the outer layer of the skin on my face .. but in the cold I had not felt it. (UNTIL IT WARMED UP.)

Serious pain action there for a couple of weeks.