NdFeB particles have strong magnetic properties, and the average particle size is generally measured by a gas permeable method. Currently, it is mainly used for measuring the particle size distribution by a dry laser particle size analyzer. NdFeB powder has self-ignition characteristics in the air. When the ambient temperature is slightly higher and its concentration reaches a certain level, it spontaneously ignites. It often ignites the vacuum cleaner pipe and filter to burn the vacuum cleaner. The following measures to prevent spontaneous combustion should be adopted:

　　(1) using an inert gas such as high-pressure nitrogen as the gas source;

　　(2) replacing the vacuum cleaner tube with a polyethylene tube with a smooth surface so that the particles are not deposited in the pipeline;

　　(3) Water filter vacuum cleaner.