Escape Tunnels are a means for a prisoner to escape the confines of a prison underground. The tunnel is started and first dug via a toilet and usually finishes outside the outer-most wall beyond the prison area.
Prisoners will only ever dig escape tunnels during sleep time, i.e. during the night.
As aforementioned, an escape tunnel is first dug at the base of a prison cell toilet. Before this can be done, a prisoner must acquire a digging tool. Below are few of many examples of tools that can be used to dig a tunnel:
- Wooden Pickaxe
As aforementioned, prisoners will only tunnel during the night time. As a means of fooling both the security personnel of the facility and the player themselves, a prisoner will set up a dummy to feign the idea that they are still sleeping in their beds.
Prisoners will have a preset path from their cell to the border of the prison. This is determined by a rule of path of least resistance. Prisoners will have difficulty digging through the foundations of a building, meaning digging beneath one will take much longer. Digging through walls bares the same result. Perimeter Walls are especially tough and are forged with solid concrete. It will take your prisoners an exceptionally long time to dig through these. Therefore if it is possible, prisoners will attempt to avoid walls and buildings and tunnel through softer, less resisting ground.
Though walls will slow a prisoner's tunnel speed, large pipes will accelerate it. In light of this, it is unwise to install large pipes in the following areas:
- In or around cell blocks.
- Directly under walls and fences.
Doing so will allow prisoners to tunnel faster and reach freedom before being detected.
Prisoners will always dig the shortest route to the exterior of your facility. They will continue to dig until they reach an insecure area (usually the edge of the map). They will dig upwards, resurface and then complete the escape on foot.
Prisoners cannot dig underneath naturally-existing water.
The speed at which a prisoner can dig a tunnel can be increased by working co-operatively with other inmates. You will usually find that prisoners are assisted by neighbouring prisoners in parallel or opposite cells. Inmates in individual cells will not start the dig altogether from a single cell's toilet. They must all start their own, individual tunnel first and then link these tunnels underground to work collectively.
As of Alpha 34, multiple prisoners digging the same tunnel yields diminishing returns. It takes 4 prisoners to dig twice as fast as just 1 prisoner. It takes 11 prisoners to dig three times as fast as just 1 prisoner.
Despite being hidden underground, there are several ways an escape tunnel may be detected.
- A guard searches a toilet where a tunnel has been initially dug.
- A guard searches an escapee's bed and discovers the dummy in place of the prisoner.
- Security personnel notice the absence or delayed arrival of an inmate during roll call.
- A guard dog scratches at the ground whilst passing over a hidden tunnel.
- A guard dog digs out an actively escaping prisoner.
However, there are certain limitations to an escape tunnel being detected. Firstly, guards are not always 100% accurate with their searches. Their chances of both searching and identifying a toilet which has been tunneled under are not always high. This percentage chance can be affected by various factors including:
- Guard exhaustion
- Staff morale & mood
Secondly, your guards may not have noticed the escaping prisoner or prisoners late arrival to roll call, in which case they will not conduct a search and reveal the tunnel. Prisoners who are tunneling when roll call is started will turn around and return to their cell to avoid suspicion. They may be able to do this before being noticed.
Thirdly, guard dogs are not 100% accurate with their detection of a tunnel either. Guard dogs are still dogs and will do "normal dog things". Scratching at the ground is normal behaviour and won't always indicate a tunnel exists beneath the prison grounds. Whether or not a tunnel does exist, a yellow flag will appear where a guard dog has scratched.
One major factor which affects a guard dog's ability to uncover a tunnel is Warden J.W. Periwinkle. Selecting him as a warden will give guard dogs a 50% chance of fully uncovering any tunnels they detect.
The only 100% surefire way to uncover a tunnel is to manually and directly search the suspected toilet individually with a single search.
When a tunnel is uncovered, all connecting tunnels and routes are rumbled and revealed. Any prisoners actively digging during the time of detection will resurface and make a second desperate attempt to escape your facility on foot. These impromptu "plan B" escapes more often than not - fail - and will land all the involved inmates with an "escape attempt" punishment, in line with your prison policy.
Removal & Cleanup
Once a tunnel is rumbled, its entirety will be revealed. The cells they intersect will become "incomplete/invalid" as they're not technically secured by walls and a door. Tunnels can be filled in and removed by using the remove tunnels tool via the foundations tab. Tunnel removal costs $20 per square meter.
Strategy & Tips
- Where a dog has scratched at the ground, a yellow flag will be placed in the same spot. A single flag may not point towards a tunnel existing, but multiple flags in a row is a big sign that there may indeed be a tunnel beneath.
- If you do have a network of large pipes built close to or underneath your cell blocks, organise dog patrols around these areas.
- Avoid using fences as the outermost wall of your facility. These no longer slow down prisoners that are digging. Instead, use brick, concrete or perimeter walling.
- Prisoners digging escape tunnels during the night won't be able to reduce their sleep needs. During the day, prisoners with confusingly high sleep needs could be a sign that they are digging tunnels.
- Hire enough handlers and dogs to ensure that all your dog patrols are monitored constantly.
- Up the security in and around areas yielding valuable dig tools, e.g. kitchen, workshop and forestry. Install metal detectors and conduct regular searches.
- If any prisoner has a digging tool, they may be able to dig tunnels from their or any toilet.
- Prisoners will usually only dig tunnels if they have a high freedom, security or family need.
Perhaps the best way to completely eradicate the possibility of prisoners tunneling is to replace every sleep period with a free-time period in the prisoners' regime. Prisoners can still sleep during free-time but prisoners can only tunnel during sleep periods. Another way could be to simply treat prisoners better (see to it that all needs are met and that the prisoners are well cared for).
Escape Mode (Console)
In Escape Mode when you're digging a tunnel and you get the 'escape artist' trait, you can get your tunnels less of a chance of being discovered. At level 5, you have the capability to 'peek out' of escape tunnel entrances.