1. Gas detection before operation
In order to ensure the safety of operators, before operation, the inspector should be at the windward side outside the confined space, and use the pump type gas detection alarm to detect different positions in the confined space. For those who are restricted by the area or facilities around the entrance and exit and are likely to be impacted by the internal airflow, they should wear corresponding respiratory protective equipment. The detection points shall be arranged from the entrance and exit along the direction of personnel entering the confined space. The detection in the vertical direction shall be carried out from top to bottom, at least from top, middle and bottom, and the detection in the horizontal direction shall be carried out from near to far, at least from near and far points of the entrance and exit.

Before operation, targeted detection shall be carried out according to the type of gas that may exist in the confined space, but at least oxygen, combustible gas, hydrogen sulfide and carbon monoxide shall be detected. When the gas environment in the confined space is complex and the operating unit does not have the detection capability, the unit with the corresponding detection capability shall be entrusted to carry out the detection.

2. Gas monitoring during operation
During the operation, the following two real-time monitoring methods shall be reasonably selected according to the specific situation of the site:
(1) Individual detection - real-time monitoring in limited space
During operation, operators wear diffusion or pump type gas detection and alarm devices within the scope of breathing belt to monitor the surrounding environment in real time. This detection method focuses on the gas situation in the surrounding environment where the operator passes and stays. It can ensure that the operator can master the gas change in the limited space at the first time. It is a very direct real-time monitoring method, and also the most common real-time monitoring method.
(2) Monitoring and detection - real-time monitoring outside the limited space
During operation, the inspector shall use the pumping gas detection alarm or the remote online detection equipment set in the confined space outside the confined space to continuously monitor the confined space gas. The detection point shall be set at the height of the breathing belt of the operator and far away from the air supply outlet of the ventilator to monitor the concentration change of toxic and harmful gases in the environment.