Before changing a gas chlorine cylinder in a room, the first step should be:

Starting the exhaust vent fan before changing a gas chlorine cylinder is essential for ensuring safety in the environment where the gas is present. Chlorine gas can be hazardous, and having the exhaust fan operational helps to ventilate the area, reducing the risk of gas accumulation in case of a leak during the cylinder change. Proper ventilation is critical, as it helps to quickly disperse any chlorine gas that might escape, thereby minimizing the potential for respiratory hazards or environmental exposure.

This proactive step prioritizes the safety of personnel in the vicinity and creates a safer working environment by ensuring that any chlorine gas released during the process is adequately diluted and removed from the area promptly. Elements such as closing windows, turning off electrical equipment, and wearing protective gear are certainly important safety measures, but establishing effective ventilation through the exhaust fan is the vital first step to reduce the immediate risk associated with handling chlorine gas.