Chapter 6 - Ventilation requirements

Abstract

The purpose of ventilation is to reduce the danger in a hazardous location to a lower level or to prevent a location in a hazardous area from becoming dangerous. Types of ventilation: natural ventilation and mechanical ventilation. The presence of sufficient ventilation influences the distance and time at which a flammable gas or vapor enters its explosion range, and reaches a non hazardous concentration. Natural ventilation is capable of diluting flammable gases or vapors in the air to safe concentrations. Since the changes in wind direction and the existence of crosswinds are unknown, wind velocities alone are normally used in combination With other factors to determine the traveling distance of a flammable gas or vapor in the air: (1) The size of the source of hazard. (2) The system pressure. (3) The operating mode. (4) To determine the quantity of the flammable gas or vapor released to the atmosphere —small or large. Natural ventilation is present in outdoor locations, and mechanical ventilation can be used in indoor locations.. . There are two types of mechanical ventilation: a “pressure fan” that pressurizes an enclosed space, and an “exhaust or suction fan” that causes a negative air flow in the location. In providing natural or mechanical ventilation, it is important to consider the presence of obstructions. A pressure fan can be installed in an enclosed space. However, setting up the location for a suction fan depends on the vapor density of the flammable product. Safeguards are required because mechanical ventilation can break down. Either safeguards can prevent the failure of the ventilating system or warn against it . There are two types of safeguards available: type “A” and type “B”. The type “A” safeguard is a redundant ventilating system which operates on loss of ventilation. The type “B” safeguard is only an audible and visible alarm system that operates on loss of ventilation.