焊接和相关工艺是许多工业领域中必不可少的工艺，但同时也会产生大量的焊接烟尘。这些烟尘中含有许多有害物质，如铬、镍、铅、锰、铜等，对工人的健康和安全造成威胁。因此，为了保护工人的健康和安全，需要采取措施来捕集和分离焊接烟尘。

ISO 21904-4:2020标准规定了捕集设备的最小空气流量的测定方法。该标准要求在实验室条件下进行测定，以确保测定结果的准确性和可重复性。测定方法包括使用风速计和烟雾发生器来测量捕集设备的最小空气流量。在测定过程中，需要考虑捕集设备的类型、形状、尺寸、位置和工作条件等因素。

该标准的实施可以帮助企业选择合适的捕集设备，并确保其能够有效地捕集和分离焊接烟尘。同时，该标准也可以帮助监管部门对企业的焊接烟尘控制措施进行监督和检查，从而保障工人的健康和安全。

相关标准
ISO 21904-1:2020 Health and safety in welding and allied processes — Equipment for capture and separation of welding fume — Part 1: General requirements
ISO 21904-2:2020 Health and safety in welding and allied processes — Equipment for capture and separation of welding fume — Part 2: Requirements for testing and marking of separation efficiency
ISO 21904-3:2020 Health and safety in welding and allied processes — Equipment for capture and separation of welding fume — Part 3: Determination of the minimum air volume flow rate of air-cleaning devices
ISO 15012-1:2016 Health and safety in welding and allied processes — Equipment for capture and separation of welding fume — Part 1: General requirements (ISO 15012-1:2016)
ISO 15012-2:2016 Health and safety in welding and allied processes — Equipment for capture and separation of welding fume — Part 2: Requirements for testing and marking of the capture efficiency of welding fume extraction devices (ISO 15012-2:2016)