Ask A Scientist© Environmental Earth Science Archive

name         Ismet H.
status       student
age          16

Question -   What are safety the conditions under for work in
environments where fine particles mix with air...please help!
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Fine particles in air present a number of safety issues
1. Fine particles in air can explode, because a large surface area of a 
combustible substance is
exposed to air. Even metal powders can be dangerous.
2. The chemical composition of the dust is important. Four classic 
examples are: asbestos,
silica, coal, cigarettes. Asbestos (at least certain crystaline types) has
been shown conclusively to cause a rare form of lung cancer. Silica dust
causes a lung disease called "silicosis". Coal dust causes a lung ailment
called "black lung disease". Of course cigarette smoke (which is a fine
particle size dust) has been shown to cause lung cancer.
3. The particle size of the suspended substance is important. Large 
particles are relatively
safe (assuming the substance is not intrinsically toxic) because large
particles are captured before they enter the lungs. Smaller particles
(sub-micrometer) form what is called in the public health literature as
"respirable dust". These particles remain suspended in inhaled air and are
deposited (some permanently) in the lungs. Extremely small particles
(nanometer size) are even more insidious. Not only do they remain suspended
in inhaled air and are deposited in the lungs, but because of their size is
the same order of magnitude as red blood cells they can move across lung
tissue and enter the blood stream. This makes nano-sized particles of what
otherwise might be considered "harmless" a hazardous material.
     "Dirty bombs" are a timely illustration of concern about nano-sized
particles. "Dirty bombs" are fissionable metallic materials (e.g. uranium or
plutonium) wrapped with conventional explosives (e.g. dynamite). These
metals are pyrophoric, i.e. the burn spontaneously when heated. In the case
of  Uranium the ignition temperature is only a few hundred degrees Celsius.
When the dynamite is detonated, the fissionable materials ignite forming
nano-sized oxide "smoke". This is not hypothesis. It is thoroughly
documented. Standard "gas masks" offer no protection against particles this
small. If inhaled the radioactive metal oxide dust can pass through the
lining of the lungs directly into the blood stream. This maximizes their
toxicity. These substances emit alpha particles, which are relatively
harmless if the source is sitting on your desk. Alpha particles cannot
penetrate skin for example. However, inhaled or ingested, the same harmless
substance becomes very dangerous because they are now INSIDE THE BODY. What
makes dirty bombs more insidious is that it is almost impossible to
decontaminate an affected area. The nano-sized particles settle out on the
ground and can be re-distributed by wind, machinery or even walking. And
because of their size they tend NOT to settle out, but rather be dispersed
by wind.

Vince Calder
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The question of working in a dusty environment is one for the "occupational
safety" experts.  It is in the area of "respiratory protection."

Scientists and engineers are not familiar specific guidelines and rules for
keeping people safe in a dusty environment.  In fact, we scientists are not
even allowed to choose our own respirators.  We have experts who we call who
know all about the problems of toxic and non-toxic dusts and get the right
mask for us.

The most information can be found from OSHA.gov.  Also, all the major
respirator and mask manufacturers (e.g., 3M, MSA, Norton) have guidelines to
guide customers to choosing the correct mask.

There are some dusty environments which pose an explosion hazard too.  If
you work where there is a lot of coal dust or flour dust, the dust can
explode if there is a spark.

Bob Erck
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