Mail-processing facility

Air samples checked for pathogens

Federal mail

Non-federal mail

Transported to irradiation facility in New Jersey

Mail is heated

Containers of mail and packages scanned


At the nation’s more than 200 mail-processing facilities, as envelopes travel along conveyor belts to be scanned and bar-coded, a machine about the size of an office copier takes periodic air samples to track for biological agents.


Once mail with federal addresses is sorted at a Washington facility, USPS trucks it to a New Jersey irradiation facility operated by Sterigenics, a company known for its medical sterilization equipment.


Federally addressed mail are heated to temperatures often exceeding 150 degrees.


Large containers holding first-class mail and packages are scanned by a high-energy electron beam or X-rays to kill potentially harmful biological agents, including anthrax.

NOTE: According to postal inspectors: Magazines, catalogues and such mail as credit card solicitations are not screened further because the USPS considers the senders trusted sources. Priority mail and express mail packages — which require return addresses and tracking numbers and must be dropped off in person or handed to a letter carrier — are not run through biological detection machines, because threat assessments have deemed such inspections unnecessary.

Positive results are from preliminary tests. Further analysis and confirmation can take 24 to 48 hours.

SOURCE: U.S. Government Accountability Office.