Folks,

I have done extensive experimental testing on both the flashpoints of 
solutions and also experimental characterization of the vapor above 
aqueous solutions.

Aqueous solutions are complicated by non-ideal behavior.

Clearly, if the solution is ideal, then the addition of water will 
increase the flashpoint temperature, reducing the hazard.

However, if the solution is non-ideal, this may not be true.

If the solution forms a minimum boiling point azeotrope, then the 
addition of water will REDUCE the flashpoint temperature and increase 
the hazard.

Thus, by adding water the flammability hazard is increased!  This is 
completely opposite of what one would expect!

This is true also of other non-aqueous solutions that form minimum 
boiling point azeotropes.

Common practice is to assume that the flashpoint of the mixture will be 
no lower than the lowest flashpoint of any of the pure components.

This is not true with minimum boiling point azeotropes.

To do a proper assessment, one would need to know if the solution forms 
a minimum boiling point azeotrope with water.  This requires VLE data 
which is not commonly available.

I have experimental flashpoint data on the following systems:

Isobutanol - toluene - min. boiling pt azeotrope
Secbutanol - water - max. boiling pt. azeotrope - flashpoint increases
Ethanol - heptane - min. boiling az.
Methanol - octane - min. boiling az.
Ethanol - octane - min. boiling pt. az.

Thus, it depends on a case by case basis and no general statements can 
be made.

Dan Crowl
Professor
Department of Chemical Engineering
Michigan Tech University
crowl**At_Symbol_Here**mtu.edu


Carl Zipfel wrote:
> I went down this road many years ago and gave up.  The problem is that the
> only acceptable test of flammability is the "flash point".  The flash point
> defines flammability, and is what is accepted by the EPA, OSHA, and more
> importantly the insurance companies.  While the solvents that you mention
> are miscible, once a little heat is applied they will separate and form a
> flammable mixture in the air. All flammable solvents mixed with water should
> be treated, handled, and stored as flammable liquids.
>
> Carl Zipfel, csp
>
>
> ----- Original Message ----- 
> From: "Hadden, Susan [PRDUS]" 
> To: 
> Sent: Monday, January 29, 2007 2:36 PM
> Subject: [DCHAS-L] Aqueous/Flammable solvent mixtures
>
>
>   
>> Many of our researchers use aqueous mixtures of miscible flammable
>>     
> solvents
>   
>> for their LC work. They often have questions about storage and whether to
>> treat them as flammable or not. I've been looking for data that might show
>> me flammability as a function of concentration for the common solvents
>>     
> such
>   
>> as CH3CN, MeOH, EtOH, IPA, etc. I've checked OSHA, NFPA and ASTM but can't
>> find any solvent specific data. Does anyone know where I might find that
>> information?
>>
>> Thanks,
>>
>> Susan Hadden
>> Senior Occupational Safety Specialist
>> J&J PRD Environmental, Health & Safety
>> 1000 Rt 202, PO Box 300
>> Raritan, NJ 08869
>> 908-704-4295 (ph), 908-707-9211 (fax)
>>     

Previous post   |  Top of Page   |   Next post