A system comprising: a monitoring unit that includes a sensor to analyze components of a first gas that has a possibility of including first components; and a pre-separation unit disposed upstream of the monitoring unit, wherein the pre-separation unit includes: a first separator configured to remove the first components from the first gas; a first supply line that is configured to supply the first gas to the monitoring unit; a second supply line that is configured to supply a second gas that has passed through the first separator to remove the first components from the first gas, to the monitoring unit; and an automatic valve station that is configured to periodically switch between the first supply line and the second supply line to alternately supply the first gas and the second gas to the monitoring unit, and the system further comprises a control module configured to control the automatic valve station, wherein the automatic valve station includes a first valve that is configured to emergency shut off the first supply line in a short time when the monitoring unit has detected the first components that include a component which contaminates the sensor, and a second valve that is configured to emergency shut off the second supply line when the monitoring unit has detected the first components that include a component which contaminates the sensor. a monitoring unit that includes a sensor to analyze components of a first gas that has a possibility of including first components; and a pre-separation unit disposed upstream of the monitoring unit, wherein the pre-separation unit includes: a first separator configured to remove the first components from the first gas; a first supply line that is configured to supply the first gas to the monitoring unit; a second supply line that is configured to supply a second gas that has passed through the first separator to remove the first components from the first gas, to the monitoring unit; and an automatic valve station that is configured to periodically switch between the first supply line and the second supply line to alternately supply the first gas and the second gas to the monitoring unit, and the system further comprises a control module configured to control the automatic valve station, wherein the automatic valve station includes a first valve that is configured to emergency shut off the first supply line in a short time when the monitoring unit has detected the first components that include a component which contaminates the sensor, and a second valve that is configured to emergency shut off the second supply line when the monitoring unit has detected the first components that include a component which contaminates the sensor. a first separator configured to remove the first components from the first gas; a first supply line that is configured to supply the first gas to the monitoring unit; a second supply line that is configured to supply a second gas that has passed through the first separator to remove the first components from the first gas, to the monitoring unit; and an automatic valve station that is configured to periodically switch between the first supply line and the second supply line to alternately supply the first gas and the second gas to the monitoring unit, and the system further comprises a control module configured to control the automatic valve station, wherein the automatic valve station includes a first valve that is configured to emergency shut off the first supply line in a short time when the monitoring unit has detected the first components that include a component which contaminates the sensor, and a second valve that is configured to emergency shut off the second supply line when the monitoring unit has detected the first components that include a component which contaminates the sensor.