Abstract-Water is a necessity of life to humans and animals. In Malaysia, Government Link Companies (GLC) or Private Companies manages most of the water treatment plants. Chlorine gas is used as one of the water treatment media to treat raw water that will then be distributed for public or commercial usage. The large volume of Chlorine gases used and stored in these treatment plants has the potential to create a disaster if it leaks. Objective of this paper to highlight a result of Local Exhaust Ventilation (LEV) monitoring system and their performance test in controlling of air flow from the chlorine gas building to prevent leakage and spread to the surrounding environment. Methodology used follows the American Governmental Industrial Hygienist (ACGIH). The Chlorine Gas leakage system is checked and verified by using ACGIH Standard. Finally as a result, all the measured parameters (velocity, flow rate, face velocity and brake horse power (bhp)) show that the measurement and monitoring system of LEV are complied with ACGIH Standard and Local Law and Regulations.Index Terms-Chlorine gas, local exhaust ventilation (LEV), American governmental industrial hygienist (ACGIH), occupational safety and health (OSH).