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Isocyanates and activated charcoal adsorption (long)

Subject: Isocyanates and activated charcoal adsorption (long)
From: "PHINNEY,HARRY K (HP-Corvallis,ex1)" <>
Date: Wed, 28 Feb 2001 13:49:38 -0800
Trevor Boicey wrote:
>> (my words)
>> Isocyanates are a very real health concern, and should not be taken
>> My understanding is that normal activated charcoal respirators will
>> out isocyanates, but such respirators are not NIOSH approved

>  From my research, it appears that that is very much untrue.

>  Activated Charcoal respirators will not filter
> isocyanates.

I'd be very interested to read a reference stating that as fact. I know that
respirator manufacturers generally will not recommend them anymore, but I
still have not read anything authoritative stating that the normal
cartridges will not adsorb them. Again, it is certain that there is no (or
at least insufficient) warning odor from isocyanates, and it is thus
impossible to know when a cartridge is failing.

The following is cut & pasted from the Detco/Sterling paint web site

---------------------------From Detco Web Site-----------------------
A fresh air supply to a full face mask is the only totally safe method of
applying urethanes and primers by spray, for the continual positive pressure
from the air source keeps all airborne contaminants away from the eyes, nose
and mouth. Use of a disposable paint suit keeps over spray off the skin for
further safety.

Lacking a fresh air supply when spraying or brushing, use the best possible,
best fitting, activated charcoal filter respirator mask, changing filters at
any time airborne solvents or isocyanates are smelled or tasted. One's
threshold to detect solvents is diminished by solvent contact with taste and
smell receptors, hence care must be exercised when working with urethanes
and epoxy primers over extended periods.  So to be safe, change respiratory
cartridges often, even if airborne vapors are not smelled or tasted.
-------------------------End Excerpt------------------------------------

I also found the following bit in a document on the web
site (note that APR represents Air Purifying Respirators, and PEL is
Permissible Exposure Limit):

-----------------------Begin Excerpt------------------------------------
OSHA and the National Institute for Occupational Safety and Health (NIOSH)
historically held that APR should be used only in situations where (1) an
adequate supply of
oxygen (defined as greater than 19.5% in the air in the environment) is
available; (2) the
atmosphere is not Immediately Dangerous to Life and Health (IDL); and (3),
for vapors and
gases, the chemical has suitable warning properties to allow the respirator
user to detect failure of
the filtration or absorption cartridge on which the protection depended. The
latter consideration
made it impossible for APR to be used to protect against overexposure to
isocyanates because the
odor threshold was greater than the PEL.
-----------------------End Excerpt----------------------------------------

A friend and former roommate of mine painted with Imron for several years in
the 1970s prior to the widespread knowledge of the dangers of isocyanates.
At that time Imron and its catalyst carried exactly the same warnings as
other paints. He became highly sensitized to isocyanates, and suffered
_severe_ asthma attacks in the presence of them. If I opened a container of
Imron on the other side of the garage from him he would have breathing
difficulties within some number of seconds. He could, however, breath fine
if he was wearing a fresh respirator cartridge, and would (somewhat
reluctantly) still spray the stuff, but would change the cartridge

>   I was able to discover references to a special "cartridge mask"
> where the single-use cartridges were designed to combat isocyanates.

3M for some period of time sold non-refillable masks that they labeled as
appropriate for use with isocyanate bearing paints, but that were not NIOSH
approved for such use. I haven't seen any of these for a few (several?)

>   Forced air, or no modern paints.

That's a fine and reasonable stance. Again, I'm not advocating that people
treat this lightly. I am, however, still of the understanding that activated
charcoal respirators will adsorb isocyanates. The failing of these
respirators is in the lack of warning odors signaling the end of
effectiveness of the cartridge.

Harry Phinney

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