staff went into the towers without radios. According to the Commission report and news coverage, this was true of NYPD, Port Authority Police Department (PAPD), and FDNY personnel. Regardless of any radio coverage problems, these persons could not be commanded or informed by radio. In any incident of this scale, self-dispatched staff without radios would likely be a problem. Even if a cache of radios were brought to the scene to hand out, the scale of this incident would be likely to overrun the number of radios in the cache. NIST concluded, at the beginning of the incident, there was an approximate factor of five (peak) increase in radio communications traffic over a normal level. After the initial peak, radio traffic through the incident followed an approximate factor of three steady increase. FDNY recordings suggest the dispatch personnel were overloaded: both fire and EMS dispatch were often delayed in responding to radio calls. Many 9-1-1 telephone calls to dispatch were disconnected or routed to "all circuits are busy now", intercept recordings. Voice radio systems NIST calculated that about one third of radio messages transmitted during the surge of communications were incomplete or unintelligible. Documentary footage suggests the tactical channels were also overloaded; some footage captured audio of two or three conversations occurring simultaneously on a particular channel. In this study of WTC incident communications, radio systems used at the site had problems but were generally effective in that users were able to communicate with one another. A 2002 video documentary 9/11 by Gedeon and Jules Naudet, (referred to as the documentary) was reviewed. It captured audio from hand-held radios in use at the incident and showed users communicating over radios from the lobby command post in the North Tower. 26 Red Book audio CDs of New York City Fire Department radio transmissions, covering the incident's initial dispatch and the tower failures, were reviewed. These CDs were digitized versions of audio from the Fire Department's logging recorders. In addition, text on an oral history CD with transcripts of fire personnel debriefed on the incident were reviewed. NYPD and PAPD systems in 2001 In 2001, the NYPD used Ultra High Frequency (UHF) radios and divided the city into 35 radio zones. Most hand-held radios had at least 20 channels: while not all officers had all channels, all officers had the ability to communicate citywide. As a characteristic of physics, UHF signals penetrate