Portable blast machines are designed to be moved on the jobsite by one or more personnel. Portable machines are offered commonly in pressure release models, this means that every time the blast operator releases the deadman handle the pressure vessel depressurizes and then repressurizes once the deadman is held down. Pressure hold models cut the flow of air and abrasive when the operator releases the deadman while keeping the vessel pressurized, these models are helpful for uses requiring frequent start and stop of blasting. It is recommended to always use a lid and screen for the blast machine to keep debris out of the machine and prevent clogging.