Gas treatment system

A gas treatment system comprising:

• a main exhaust line for guiding exhaust gas to a gas treatment apparatus;
• a bypass line for guiding the exhaust gas to equipment other than the gas treatment apparatus;
• an upstream exhaust line for guiding the exhaust gas to the main exhaust line and the bypass line;
• and
• a three-way valve capable of switching a flow of the exhaust gas from the upstream exhaust line to the main exhaust line or the bypass line,
• wherein the bypass line includes:
• a gate valve;
• a gas introduction pipe through which a second gas is introduced between the three-way valve and the gate valve;
• and
• a pressure gauge configured to detect pressure between the three-way valve and the gate valve, and
• if the three-way valve discharges gas to the main exhaust line, the gate valve is closed to form a closed flow path between the gate valve and the three-way valve, and in a state where the second gas has been introduced into the closed flow path from the gas introduction pipe, internal leakage in the three-way valve is detectable using change in pressure detected by the pressure gauge.