Page 433 - Advanced Mine Ventilation

402 Advanced Mine Ventilation

Table 24.1 Minimum Thickness for Explosion Proof Stoppings

Thickness for a
Country Material Formula 20 3 6 ft Entry (ft)

United Kingdom Rock/Cement Grout WþH þ 2 15
t ¼
2
Germany Rock/Cement Grout e 5e7
Poland Rock/Cement Grout e 7e12

United States [4] Rock/Cement Grout WþH 13
2

United States [4] Sandbags W H 40
3
United States [4] Loose Rock or Sand 3 W 60

Chapter 23). They are also known as “bulkheads.” They are typically made of two end
walls (3e4 ft thick masonry) 10e50 ft apart depending on local law, materials, and
method of construction. The gap between the walls is tightly filled with bulk materials
and Class A cement grout. Concrete, gypsum and anhydrite powder, fly ash, and
bentonite are also used in some cases. In the United States, many seals are made of
concrete blocks, Omega 384 foam blocks, cementitious or polymer foam seals. Two
sampling tubes with steel caps are also installed as in the permanent stopping for sam-
pling the air in the sealed area.
Using Eq. (24.1) again and assuming that the minimum explosion pressure can be
as high as 640 psi, the thickness of an explosion-proof stopping should be at least 16 ft.
Minimum thickness required in different countries are listed in Table 24.1.
In the author’s experience, two masonry walls of 4 ft thickness with at least 10 ft of
space between the walls filled with rock and pressurized cement grout provide the best
protection against any explosion in a sealed area.

24.2 Inertization of the Sealed Area

To expedite the quenching of fire in a sealed area, two options are generally available:
Flooding with water or
Inertization with a nonreactive gas such as N 2 or CO 2 .

24.2.1 Flooding With Water
Flooding with water is an excellent technique for the extinction of fire under suitable
circumstances, such as inclined workings. It first cools the fire and secondly excludes
all oxygen making sure the fire would be extinguished promptly. It also cools the roof
and floor and fills them up with fines preventing all access to air/oxygen. No serious
damage is done to mining equipment by waterflooding.