bomb shelter plans

Bomb Shelter Plans – published on June 6, 2020

The key factors when laying out your bomb shelter

·       Carefully sequencing your shelter layout will remove odors, moisture, and the carbon dioxide that the occupants exhale. It will also allow you to create an airlock that will let you to safely exit and re-enter your shelter without allowing unfiltered toxic air to migrate into the protected space.

·        Every shelter should have a secondary egress capability. The shelter drawings below all show a door and an emergency escape hatch.

Shelters are sealed environments that require ventilation to sustain life. The NBC air filtration system will create positive relative pressure inside the shelter. In other words, there will be more air pressure inside the shelter than outside. This “overpressure” will ensure that if there are any small leaks, the air inside will flow outward and prevent unfiltered toxic air from migrating inside through leak points.

To have true ventilation in an enclosed space, you need to bring air in from the outside and then exhaust it back out. As you scale up the size, it becomes easier to fit everything, so we will use a relatively small 10 foot by 30 foot (3 meter by 9 meter) shelter as an example.

The door and hatch

We’ve placed a blast door on one end and an escape hatch on the other end:

The air filtration system

Now we will add a nuclear, biological, and chemical (NBC) air filtration system on the intake ventilation pipe and an overpressure blast valve on the outflow ventilation pipe. The overpressure blast valve will allow air to be exhausted from the shelter, but it will shut automatically when presented with a high pressure event from the outside. It’s a one way check valve that only allows air to exit so unfiltered toxic air will not back up into your shelter if there is a wind gust or a nearby detonation that causes a spike in the air pressure. The airflow will diffuse as it transits the length of the shelter, but it is shown here from intake to exhaust to show the point of entry and exit:

This is how most bomb shelter plans are laid out. Air is brought in on one end and let out the other end. But nothing is done with this stream of filtered air. It’s a wasted resource, but we will fix that.

The airlock and hatch tunnel

There are now significant upgrades to the safety of this shelter with the addition of two corner walls with doors, another overpressure blast valve, three floor drains, and a shower:

1. There is now a decontamination airlock that allows safe re-entering of the shelter. You enter the airlock from the outside, decontaminate yourself with the shower while you wait for the airlock to purge the outside air, stow your suite and mask over the floor drain, and then re-enter the shelter.
2. The inner doors will function as a secondary barrier if the blast door or hatch is breached by a malicious person. A strict protocol of having only one of the three doors or the hatch open at a time will ensure that unauthorized people are denied entry.
3. The walls under the escape hatch form a vertical tunnel and are a barrier to whatever comes through the hatch lid. Radiation and bullets move in straight lines and will engage the walls at a steep angle, increasing the effective thickness and protection factor of these interior walls.
4. A four inch high concrete threshold under the three doors will keep shower water inside the airlock and rainwater inside the hatch tunnel if the hatch lid is inadvertently left open.

The design and protocols of an airlock

Be sure and see this article on bomb shelter airlocks.

The bathroom

Next, a small room with a toilet and sink is tucked in next to the airlock. A normal residential interior door with a louvered vent in it will provide privacy but keeps the shelter and bathroom in the same airspace:

Full disclosure: as an Amazon Associate I earn from qualifying purchases. The convenient links below will take you directly to the items on Amazon and help support this website. Thank you very much!

Any door can have a vent installed in it. This door vent from Amazon is 90 square inches (0.06 square meters): Bathroom Door Air Vent Grille 455mm x 135mm / 18″ x 5.3 inch Two Sided Ventilation Cover (White)

The airflow

Now let’s close all the doors and see how the air flows through this shelter. The entire shelter is one air space, but the odors and moisture in the bathroom and the unfiltered air in the airlock are downwind from the main part of the shelter. The air in those spaces is sequentially removed from the shelter. The two overpressure blast valves will only allow air to move one direction through the airlock:

This layout maximizes the survivability of this small shelter without increasing its footprint. Bomb shelter plans that do not include an airlock are missing a very important capability and under-utilizing the airflow from the NBC air filtration system.

A backdraft damper that is at least the same size as the ventilation pipes  can be used instead of the inner overpressure blast valve. A margin of safety is recommended so consider a larger size.

At Amazon:

• AC Infinity 6″ backdraft damper, one-way airflow ducting insert with spring-loaded folding blades
• AC Infinity 8″ backdraft damper, one-way airflow ducting insert with spring-loaded folding blades
• Backdraft damper: 10 Inch
• ALDES 12 inch round spring loaded backdraft damper

Six, eight, ten, and twelve inch backdraft dampers.

Scaling it up and adding partitions

Now we’ll look at how to best flow air through a larger 18 foot by 40 foot (5.4 meter by 12 meter) shelter with multiple rooms. Note that the filtration system is now in a mechanical room and the air flows through the two bedrooms and a kitchen before the entering the bathroom:

Vents between rooms

The louvered vents that allow this airflow are at opposite corners of each room and alternate between being placed high and being placed low on the wall. Be sure and allow for more airflow through the vents than the filtration system puts out. The way you ensure this is to calculate the area of the round ventilation pipes (πr²) and ensure the louvered vents have more area. Example: 6 inch ventilation pipes have an area of 28.26 inches (3.14 x 3 x 3). An 8 inch by 8 inch vent has an area of 64 inches (8 x 8). Since the vents will have louvers and possibly screens, doubling the area of the vent like this example is recommended.

At Amazon this vent has 144 square inches (0.09 square meters): Air Vent 81202 12″x 12″ Aluminum, White 12×12 WHT ALU Louver

We want to create one airspace out of many rooms without introducing resistance to the airflow. If you choke it down anywhere, you choke it down everywhere. The vent between the kitchen and the bathroom is right above the alcohol stove where it can remove the heat, odors, moisture, and mitigate the potential for carbon monoxide and fuel vapor leakage. If you are going to operate anything that burns fuel in your shelter, all of the interior doors should carry a fire rating and you should have multiple smoke and carbon monoxide detectors.

Alternate airflow through the shelter

When all of the interior doors are closed the living room does not receive direct ventilation. Now let’s look at what happens when the doors to the mechanical room and the airlock are open:

Most of the air flow will route through the living room to provide ventilation. Note that in daily shelter life, all of the interior doors will probably be opened many times and there will be adequate ventilation throughout the shelter.

The most vulnerable time is when people are sleeping. If the interior doors are shut at night, the air flow to the bedrooms will be prioritized. If there is a fuel leak in the kitchen, the vapors will be taken out of the shelter through the bathroom and airlock.

The safest place to store fuel is outside the shelter, but anything outside the walls cannot be counted to be there when you need it. The safest place inside the shelter to store fuel is in the airlock. It is downstream from the rest of the shelter and has a one way check valve to stop combustible fuel vapors from migrating into the living spaces. Ensure there are no ignition sources wherever you store fuel.

The take-away

The airflow from an NBC air filtration system is an underappreciated resource that can be exploited to maximize the survivability of a shelter. The correct sequence is:

1. The spaces where you will spend the most time – the living room and bedrooms.
2. The kitchen area where food is prepared.
3. The bathroom.
4. The airlock

Most shelter manufacturers have many layout drawings on their websites. They place the critical components into their shelter designs without regard for the proper sequence that will optimize the airflow from the filtration system. Fortunately, they all seem to advertise that they will do custom bomb shelter plans. No matter what kind of shelter you purchase or build, you need to specify the correct sequence of the components and rooms to your shelter supplier, architect, or contractor.

Next article: Bomb shelter airlock – principals and protocols

At Amazon: Best Sellers in Safety and Security Full disclosure: as an Amazon Associate I earn from qualifying purchases. The convenient links below will take you directly to the items on Amazon and help support this website. Thank you very much!