This was copied from an EZboard post by a David Ferguson:
I recently ran across this on a vintage board (that claimed they got it from
a Kennedy Space center safety report), and it presented a problem I had
never
considered before.
Subject: Aluminum dust explosive danger
I'm sending you the following details of an incident that has happened to me
while using a 1" belt grinder. I feel it might be applicable for publication
in the newsletter as a warning for others. Although I was using a commercial
model (Delta model 31- 050) I feel it is just as applicable to any type
grinder, commercial or home made.
On 25 January, I was using the grinder to smooth the edge of a hacksaw cut
on
a 2" length of 1.5" angle iron. I had been grinding for about 1.5 to 2
minutes when there was a loud "THUMP" accompanied by an approximately 2-foot
diameter brilliant yellow- orange fireball. The fireball lasted no more than
= second and then completely extinguished itself. It completely enveloped
the
machine and my hands to half way up my fore arms and to the top of my
stomach.
As soon as it went out it was obvious that I had suffered some serious burns
to my hands. Besides large white areas on the heel of each thumb and the
palm
of my left hand, the skin was hanging from the heel of both hands, from my
little finger to my wrist, and from the finger joint of my left hand. Also
the right cuff of my shirt was smoldering, my face felt burning, and I could
hear the front of my hair sizzling. Nothing on the bench was burning. The
only evidence was a few streaks of white powder on the bench top and on a
few
items lying on the bench. The workshop was filled with dense white smoke
with
very little odor. My fingers and the ends of my thumbs escaped relatively
unscathed as they were resting on the machine's table and were protected
from
the heat flash by it.
Besides the burns to my hands, my neck, chin, cheeks, lips and the end of my
nose suffered first-degree burns and have recovered after peeling as if a
bad
sunburn. I was wearing glasses and these protected my eyes, which appear to
not have been damaged. I also lost half my moustache, > of my eyebrows, and
about 1" off the front of my hair. My eyelashes were curled by the heat but
not singed .The burns to my face were caused solely by radiant heat, as the
fireball did not come that high.
Initially I could not understand how I could have suffered such severe burns
from such a brief exposure to the heat. Later that evening after some
thinking and questioning of my son (who also uses my workshop), it became
clear what had happened. A few days earlier he had ground the heads off
about
twelve 1/8" aluminum pop rivets. Finely divided aluminum mixed with finely
divided ferrous oxide (the black powder residue from grinding steel) produce
a compound called "THERMITE". Thermite is used to fill incendiary bombs and
commercially to weld large steel items (e.g. railway rails) into continuous
lengths. It burns at approximately 3500 deg. C (6300 deg. F), hence the
extensive burns from such a short exposure time. The end result was,
excluding my fingers; I suffered deep second-degree burns to about 60% of my
left hand and 50% of my right hand.
Interestingly there is no warning of this possible occurrence in the safety
section of the manufacture's owner's manual. As a result I have sent a copy
of the contents of this letter complete with pictures of my hands to Delta
Machinery. Their reply should be interesting! In light of my experience I
feel there should be a very STRONG warning passed on to the readership as to
the dangers posed by grinding steel after having ground aluminum, unless the
machine is thoroughly cleaned of all aluminum dust. The potential is
certainly there for even more serious injury. Due to the potential
seriousness of this incident I have also sent a copy of this letter's
contents to the editors of ME, MEW and ElM in order to maximize the
dissemination of this information
Rex Burkheimer
Parts Plus Marketing Director WM Automotive Whse., Fort Worth TX
"I want to put a ding in the universe." --Steve Jobs
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