Why Does a Mine Need to be Ventilated?
Ventilation in a mine means circulation of air through that mine. For air flow/circulation to take place between any two points, there has to be a pressure difference between those points. In the same way, air circulation to take place in a mine, there has to be a pressure difference between the outside atmosphere and the atmosphere inside a mine. In the early days of mining before the advent of mine fans, such a pressure difference used to be produced by natural means. In modern times, fans are doing this job. In fact, coal mines regulations in every country require that every underground coal mine, big or small, must be ventilated by a main fan located on the surface.
When the pressure in a mine is negative, i.e. less than the outside atmosphere, the ventilation system is said to be suction or exhausting. On the other hand, if the pressure in a mine is positive, then the ventilation system is said to be blowing or forcing. Both the systems have their advantages and disadvantages. We will discuss that later when we discuss fan-ventilation.
Now we know that a pressure difference between outside atmosphere and the inside atmosphere in a mine causes mine ventilation. This pressure difference is termed as ventilation pressure. In exhaust ventilation system, ventilation pressure is negative, and in forcing system it is positive.
The instrument that is used to measure ventilation pressure is a manometer. Since water is used as a manometric fluid, the instrument is more commonly known as water gauge. The water gauge is placed in a fan drift (a tunnel at the surface connected to a fan shaft). The open end of one limb of the water gauge is exposed to outside atmosphere and the other limb to the inside of the fan drift, so that it can measure ventilation pressure. In the last paragraph we came across the term “fan-shaft “. Now what is exactly a fan-shaft? It is the shaft to which the fan-drift is connected. In exhaust ventilation system, the upcast shaft is the fan-shaft, and in forcing system, downcast shaft is the fan shaft. To prevent short-circuiting of air, the top of a fan-shaft is always covered. Such a covering is called surface air-lock.
Purpose of ventilation
The main purpose of maintaining ventilation in an underground mine is to provide there an atmosphere which is relatively free from harmful gases, dust, excessive temperature and humidity, and which contains adequate quantity of O2——– so that workers can work underground in an atmosphere which is safe and conducive to efficient working.
