To shut off the flow of gas behind a dryer, the handle on the valve should be rotated so that it is straight up, according to About.com. The appliance should always be unplugged first, notes AppliancePartsPros.com.
The gas should always be turned off at the source before attempting a repair of any gas appliance, AppliancePartsPros.com notes. Anyone attempting to repair a gas appliance should be careful to keep hair and clothing away from moving parts and should wear safety glasses when working with tools.
HomeTips.com notes that dryer lint traps should be cleaned after every load of clothing. Anyone who detects a strong odor of gas should leave the area and call the fire department from a different location.