There are four primary types of explosive-detection technology available. These are x-ray machines, which make visible the components that may indicate a bomb; metal detectors, which may help detect the components that indicate a bomb; explosive vapor detectors (EVDs), which detect the vapors from explosives (this also includes explosive-detection dogs); and neutron analysis and similar equipment that detects explosives through atomic signature. The paper advises that each type of technology has advantages and limitations. Given the need for a rapid screening of mail, EVDs, dogs, and atomic analysis are not suitable for such screening; therefore, this paper focuses on the use of metal detectors and x-ray machines. It notes that the ability to see the contents of the mail items is a major factor and advantage in the accurate screening of mail. The use of an x-ray machine or a metal detector in conjunction with an x-ray machine is more effective than the use of a metal detector alone. In large mail handling facilities, the use of a conveyor could reduce the time required to screen mail; in smaller facilities any savings in time must be calculated against the added expense of a conveyor system. The paper cautions that no machine currently available will detect all the possible types of bombs, and they will occasionally make false identifications.