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Name: Ismet H.
Status: Student
Age: 16
Location: N/A
Country: N/A
Date: August 2004


Question:
What are safety the conditions under for work in environments where fine particles mix with air...please help!



Replies:
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


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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