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List,
Please consider the following, if you're going to blast your own stuff:
Commercial sand is usually bar sand, dredged from river bars and like places.
It comes in all kinds of confusing classifications, largely depending on
local customs and names. Sand is basically silicon dioxide, and is the
product of weathered and mechanically broken down quartz from quartz bearing
rock, such as granite. All sand contains some free silica, which is present
as fines, much too small to see individual particles. This is the "smoke" you
see blowing away when you blast it, along with the paint and rust. The
unbound silica is the most dangerous component because it is present in such
fine particles, which are aspired deeply into the lungs, and which
substance is completely inert. The body can remove only so much of it by
natural defenses, so the silica that gets in finds a resting place and
remains there for life. Cumulatively, the damage mounts until silicosis
presents.
If you think about where the sand started life, in rocky mountain regions,
and how it came to be present in the bars that were dredged out to get your
sand, you begin to see other hazards.
Since the rock which gives birth to the sand is of varying origination, the
sand also contains all the other mineral components that were lodged in the
solid rock along with the quartz. These are feldspar, which is the abrasive
used in toothpaste, mica, which we have all seen in our toasters, and
various metals/ metal compounds. All of these make up the native rock. All
have their own associated handling cautions. Bar sand is also known to
contain asbestos fines, if it came from rock deposits that also contained
asbestos. (very common in the eastern portion of the US) There was a major
recall of certain brands of play sand a few years ago because it was found to
be high in asbestos.
In northern US regions, where glacial action occurred in past eras, it is
very common to find undeground sand deposits that contain sand and gravel
which originated far off to the north, where perhaps the native rock was
different. Here in New Jersey and nearby Pennsylvania, we have highly
radioactive components in sand that is mined from deposits of the "Reading
Prong", a geological name for a rocky area far to our north from which our
sands came. It has been used to make building materials for public buildings
that were later on discovered to have unsafe levels of radiation built right
into their walls! These materials decay to form radon gas, which is a known
causal agent of lung cancer, second only to smoking.
I can add to the already discouraging hazards by pointing out that sand
arrives in our sandbars by route of the rivers and streams, many of which
flow through industrial areas. Toxic materials and organic chemical poisons
often end up in the bottom sediment., where they are concentrated. We call it
sand when we go buy it, but environmental authorities call it bottom
sediment. When a river is dredged for navigation, sometimes the sediment is
deemed so toxic that it cannot even be dumped at sea, or deposited on the
banks. It must go through an incinerator first before it's safe for public
exposure. Many times, you can find a sand dredging company not far away
from the same "toxic materials", selling the very same "bottom sediment" as
sand.
What's the point of bringing this up here? The point is that sandblasting
with natural sand is much more hazardous than we would guess at first. Some
sands are "washed" before being sold, which means that a mechanical washing
process is used to clean the sand of organic debris, fine dust, and clay. It
is screened, to "sort" it into uniform granular size. It can be dried,
bagged, and made to look as clean as table sugar, but NO ONE checks it for
hazardous materials!
If you blast with a full face respirator, are you sure that all the dust
and nasties are settled around you before you unmask? If you use a supplied
air mask, where is the air being drawn from? Is it safe from blowing dust so
that you don't get it back into the mask?
There are a few industrial products around that are safer and more effective
than sand. Most are a bit more expensive, while some are about the same.
Black Beauty, a man made furnace product, is almost pure coal-furnace made
glass, which is collected as slag at the bottoms of big central station
power boilers. It is tapped off, qenched in a water tank, and collected in
large bunkers for sale to the processors. It has a razor sharp grain, is
correctly screened and washed, and has been manufactured at a high red heat
so that most, if not all, of the toxics have been burned off or left
behind. It costs a small bit more than bar sand, and is the mainstay of the
ship and boatbuliding industry.
Ground glass is available in pails and drums, (contact me for sources for any
of these if you can't find them) and it is made especially for blasting. It
is said to be free of pure silica, as it is made from already processed &
recycled glass, and it is cheap. It has a good tooth, and feeds well.
ground glass seems to be more common in Europe, but I have recently tried
it, and it does a good job. Garnet was already mentioned, and it is a
superior medium, altho more expensive. It's a crushed and screened natural
rock crystal, that is free of sand and free silica in most offerings.
My apologies for the long-windedness, but I can recall a conversation with
one of the younger members of the list recently, during which I said "..if I
could do one thing over again in my career, it would be to limit my exposure
to breathable solvents and dusts." If only we knew!
have fun, but be careful out there!
This archive was generated by hypermail 2b29 : Thu Mar 02 2000 - 22:30:40 PST