PPE, Ensembles.
Putting it all together. Dealing with hazardous materials, there are four basic ensembles known as:
|
Ensemble Name
|
Hazards
|
Features
|
| Level D | Basic construction safety | Coveralls, gloves, boots, safety glasses, hard hat, long sleeves |
| Level C | Low to moderate respiratory hazard | Respirators, disposable or chemical resistant clothing |
| Level B |
High respiratory hazard, some skin |
Pressure demand SCBA, suit can be two pieces, not air tight |
| Level A | High respiratory hazard, high skin | Full “moon suit” |
Since we want to select protective clothing that does not fail, we should examine
what causes failures. There are three basic causes: Degradation, Penetration,
and Permeation. Degradation means the physical properties of the clothing
change with time. They may become brittle, break, etc. (Like my hip waders.)
Penetration means a sharp or not-so-sharp object pokes a hole, or a hole wears
in the clothing. Permeation means that the chemical can diffuse through the
fabric. Dr. Wetterhahn was wearing latex gloves, but the dimethyl mercury permeated
the gloves. Permeation rates might be very different, even for apparently similar
chemicals. The concept of Breakthrough time is allied with permeation
rate. It is simply defined as the time from first application of a chemical
outside the clothing to the time it is first detected on inside.
Some factors that might affect permeation rate and breakthrough time are temperature and thickness of the barrier.
Here is a site with glove info including breakthrough
times. Look at one of the Chemical Resistance Charts and note two things, the great difference in breakthrough times for different glove materials for the same chemicals, and also how short some of the breakthrough times are. Try looking up your favorite chemical.