Page 168 - Advanced Mine Ventilation

148 Advanced Mine Ventilation

of alldustinair.The filter-holding unit is made of plastic but can be made of metal or
hard rubber. Although the respirator does an excellent job of dust control, some per-
sonal discomfort may arise owing to breathing resistance and facial irritation caused
by the face seal. It also interferes with normal voice conversation, as well as eye-
glasses and goggles. To eliminate these difficulties, a much lighter single-use
respirator is often used. In this case, the whole mask is made of filter material, and
it covers the entire nose and mouth area of the wearer. However, it does not form
a perfect seal against the dusty air nor is it as efficient as the replaceable, heavier
filters.

10.6.2 Air Helmets

The air helmet is a special hard hat (somewhat bigger than the conventional miner’s
hard hat) that contains a battery-powered fan, a filtration system for dust, and a face
visor. It provides protection for head, eyes, and lungs in a single unit. Although the
air helmet is much more expensive than mask filters and weighs about three pounds,
it is finding greater acceptance in US coal mines.
In the air helmet, dirty air is drawn through a filtration system by a battery-powered
fan, and the clean air is directed to the full face visor over the wearer’s face. The air
exits the wearer’s face at the lower end of the visor. The battery for the fan is carried
by the wearer on the belt.
If the air velocity is not high, the air helmet performs as well as the replaceable filter
mask with a collection efficiency of up to 84% for respirable dust, but at higher air ve-
locity, the collection efficiency appears to go down to about 50% [14]. This contradicts
the theory of dust collection, but it may be due to excessive turbulence that can recir-
culate some collected dust in the visor. Although personal protection devices can be
effective in reducing dust exposure, they are vulnerable to human errors in their clean-
ing, maintenance, fitting, and use. They should not be used for an extended period of
time, such as the entire 8-h working shift.

10.7 Optimization of Water Sprays

Water sprays come in many designs to meet specific requirements. It is a good idea to
enlist the help of a commercial spray manufacturing company for an optimal design.
The main types of sprays are as follows:
1. Hollow cone,
2. Full cone,
3. Flat spray,
4. Solid stream, and
5. Air-atomized.

Each type of spray head had several variations to meet specific needs. The type of
spray must be matched with the mining operations for best results.