WJ Seidl on thu 31 may 07
John and I have been having an interesting off list conversation=20
regarding what I wrote about water filtering
the output of a wet/dry vac. I think the information is important=20
enough to post to the list.
First, some important information. OSHA standards show the following:
"Respirable dust has been shown to be harmful to human health,
especially when silica is present in the dust. It causes a disease
known as silicosis, which can occur in three levels: chronic silicosis,
which occurs after 10 years of exposure; accelerated silicosis, which
occurs between 5 and 10 years of exposure; and acute silicosis,
which can occur within a few weeks to five years of very high exposure
to silica dust. Respirable dust consists of the dust particle size
fraction whose median diameter is 4 microns (=CE=BCm)."
(Note that the mention is of _dust_, especially dust containing silica.=20
Not just silica, ALL dust)
With John's permission, our off list conversation is shown below in=20
reverse chronological order (newest post first).
Please note the information in the second paragraph below, and compare=20
it to the information above.
We use that system for commercial applications such as stores that
generate a large amount of normal floor dust.
We're in these places once a week each. From start to finish, each vac
job takes about three hours. At the end of the operation, I go around
and check to see if there has been any redeposit of dust on to surfaces,
which is 1) an indicator that the vacuum is not performing to expected
levels, and 2) obvious dust is not going to make our customer very happy=20
in the morning.
To date, we haven't found any significant redeposit (I check with white
microfiber cloths). That is the only testing I do on a regular basis. I=20
am quite sure that
there is some dust escaping the vacuum. As to particle size, I can't
answer because I have not had it analyzed. To our customers, if it
isn't visible, it isn't there so for our use, keeping the customer
happy is good enough. Of course, silica exposure is NOT a normal concern
in vacuuming a department store.
If anyone is concerned about silica exposure, they should not be dry
vacuuming anyway. If they insist on doing so for silica removal, I
would of course recommend a HEPA filtered vacuum. However, the caveat
with HEPA filters is the same. It does not remove ALL particles. It
was designed to remove allergens and bacteria, which run in the 0.3
micron and larger range, IIRC.
Here is the blurb from the Goodway HEPA vacuum site:
HEPA Vacuum History
The need for absolute filtration arose during World War II and was
developed by the Atomic Energy Commission as part of the Manhattan
Project to produce the first atomic bomb. There was a pressing need to
address the health and safety issues raised by the handling of
radioactive dust. Research and development produced the first HEPA (High
Efficiency Particulate Air) filters for the ventilation systems used to
deliver ultra clean air to clean rooms.
In order for a filter to be certified HEPA, it must be tested and proven
to filter particles as small as 0.3 microns to 99.97% efficiency at its
designed air flow. To understand what a HEPA filter does, it helps to
understand what a micron is. A micron is 1 millionth of a meter. A human
hair is approximately 100 microns wide. Particles smaller than 10
microns are not visible to the human eye. A particle of tobacco smoke
averages 0.01 to 1 micron. Most bacteria range from 0.35 to 10 microns.
Almost all viruses, however, are smaller than 0.03 microns and HEPA
filters are not effective at trapping them.
So, to answer your question, if the vacuum is spitting out particles,
they would be smaller than 10 microns.
On May 31, 2007, John Hesselberth wrote:
> Hi Wayne,
> I'm concerned about this from an engineering standpoint. With the volum=
> of air that is being handled I suspect those bubbles would be huge and=20
> there would be no effective washing out of the dust at all. Designing a=
> scrubber that really works requires generating a huge amount of surface=
> area, i.e. extremely fine bubbles. I guess I am asking if you have=20
> really tested this to be certain it is removing the dust. Or are you=20
> just not seeing it blow back into your studio because it is so fine?
> On May 30, 2007, at 5:22 PM, WJ Seidl wrote:
>> Then it is a simple matter of installing a 5 gallon bucket in the bot=
>> of the vac, installing the pipe, and filling the bucket at least half=
>> with water (or simply installing the pipe and adding water to the vac=
>> so that the bottom elbow is covered to a depth of two inches or so. =
>> intake water bubbles through the water and exits the vacuum as it
>> normally would, minus dust, in effect creating a water bath.
WJ Seidl on thu 31 may 07
My apologies to all.
I forgot to include some important links in my last post.
OSHA is taking silicosis very seriously, and ceramics has been
targeted as one of the "most likely to occur" industries.
Here are the links.
who actually has to study this stuff to stay certified (sigh)