The Personnel Access Hatch allows maintenance crews to enter down into the Launch Facility, which contains the Launch Tube where the Minuteman missile is emplaced, as well as the launch equipment necessary to keep the missile on alert, 24 hours a day, 7 days a week, 365 days out of the year.
The first design used for the Personnel Access Hatch - PAH (of which the Malmstrom AFB continues to utilize this version of the PAH) weighed approximately 2000 to 2700 pounds. The maintenance team uses a hand operated screw jack to open the PAH.
Later versions of the Personnel Access Hatch were of a much heavier design, and weigh up to approximately 10,000 pounds. These hatches were incorporated into the design of the Launch Facilities that had either the Minuteman II or Minuteman III missile emplaced. Due to the significant weight increase attributed to these heavier access hatches, they required hydraulics in opening the PAH.
Access to the Perimeter Access Hatch is gained through a well thought out multi step procedure designed to insure the maximum amount of security for each Launch Facility. The Air Force requires that a security team accompany the maintenance team to the Launch Facility. Once both teams arrive together, security personnel remain above ground to provide security topside. This allows the maintenance team the ability to focus on the task/tasks they have been assigned to the LF to perform.
Gaining entry to the PAH and the interior of the launch facility, is called entering into the inner zone of the LF. There are security measures and equipment established for the outer zone, as well as a separate set of security equipment and safeguards for the inner zone.
For photos and description of how a maintenance crew pulls the A Plug and accesses the B Plug, follow the link below.
The A Circuit Lid is one of the first pieces of equipment that the maintenance team needs to access, in order to prepare the Personnel Access Hatch to be opened, which is essential in gaining access to the interior of the Launch Facility.
Once the maintenance team removes the A Circuit Lid, they use a combination number on the inner lid that once opened and removed, allows access to a large bolt that secures the hatch closed. Pulling that bolt back unlocks the Perimeter Access Hatch, at which point the maintenance team then uses the necessary equipment (either a scissor jack or the hydraulic system) to lift open the hatch.
Once the Perimeter Access Hatch is opened and secured to prevent it from accidently closing, the maintenance team can then climb approximately 8 to 10 feet down a 42 inch diameter shaft to get access to the top of the B Plug.
Upon arriving to the Launch Facility, the B Plug will be found raised to its upper most position, essentially closing off any access to the interior of the Launch Facility.
In order to lower the B Plug a member of the maintenance team enters a specific combination on the top of the B plug, to unlock the plug. Once the correct combination is entered, the team will have to wait patiently for another 20 to 30 or more minutes before the B Plug lowers itself down into the Lower Equipment Rooms. This is a safety feature built into the Launch Facility, given an unfriendly has somehow gained access to the B Plug, (extremely improbable) the unfriendly would also have to wait 20 minutes for the B Plug to lower itself, allowing access - which gives the security team from the Launch Control Facility time to respond to the intrusion. This strategy provides the security team additional time to arrive at the Launch Facility before the unfriendly actually gains access to the interior of the Launch Facility.
The photo above is of the B Plug taken from below, from the Lower Equipment Room. The B Plug is designed to lower itself down the length of the 42 inch diameter shaft, which then allows the maintenance team to use the ladder to climb down into the Equipment Rooms, 1 and 2. These upper and lower Equipment Rooms encircle the outer diameter of the launch tube. These rooms contain the computers, batteries, communication equipment, security equipment and other equipment necessary to monitor the missile, as well as the Launch Facility itself, and provide the ability to launch the Minuteman missile when given the command to do so.
Note the retracted lugs that are on the bottom of the B Plug. Once the maintenance team complete their tasks, and are closing up the Launch Facility, the B Plug is returned to its upper position which sits about 10 feet from the top of the Launch Facility. Those lugs then extend out and lock the B Plug in place, making it virtually impossible to lower the plug while those lugs are extended out.
The Air Force was very thorough in designing a system that provided comprehensive security to both it's Launch Facilities, as well as the Launch Control Facilities.
For more information discussing the Launch Equipment Rooms, please follow the link provided at the end of this page.
This photos shows what it looks like once you have climbed down the ladder into the Launch Facility, via the Personnel Access Hatch.
For more information regarding the Lower Equipment rooms within the launch facility, follow the link below to the section discussing the Launch Tube and its integral components.