One of the 'quirks' of local public housing is that it comes with an 'ensuite' bomb shelter - basically a room of reinforced concrete with a pair of ventilation holes. I should be able to get plug in/mains power and I know there are companies that fitted in exhaust fans to these.

TLDR: I'm trying to figure out if I can swap the fragmentation plates for the ventilation for my household bomb shelter for ventillation fans

I don't want to make substantial irreversable changes.

I'm still waiting on the keys though I have a plan of the unit, and a rough idea of where sockets and such

I have a pair of air conditioning units that blow air into the living room and ideally I'd like things set up to intake air at one vent and extake at the other

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The blue arrows represent the air conditioning units, and the two red arrows where the ventilation holes would be.

I've also got the specifications for the ventilation sleeves (and the bomb shelters)

Two 125 mm diameter ventilation sleeves shall be cast into the wall/s of each HS.

Each ventilation sleeve shall have a 6 mm thick stainless steel fragmentation plate mounted on the external face using 8 mm stainless steel bolts. See FIGURE 4.4(a) and (b).

taken from the 2017 edition of Technical Requirements for Household Shelters but there's a 2023 edition as well.

Usefully it has engineering drawings as well.

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Practically they look like this

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I can't find much reference to the 'inside' - I think this youtuber's shelter's a smaller version but that's what it is like on the inside. Here's another example - he has a portable air conditioner but ideally I'd like to avoid that. Does seem to indicate a 'standard ventsize though.

I need to be able to reinstate the 'original' plates and bolt, so the ideal would be something that'll 'just' bolt in, or need minimal modifications instead of the plate and intake/exhaust air. I've nearby sockets so something I can wire up to mains would be ideal.

This is both for 'legal' reasons (as per the specs) and if it doesn't work out I can just reinstate the original set up and pretend nothing happened.

What should I be looking at specifications/design wise to do this?

  • If an magnet holds onto the rear plate, you could think about attaching the fan assembly with strong magnets. That would allow you to minimize modifications. It should help you legal-wise as you could remove the fan without tools.
    – Martin
    Jul 20, 2023 at 7:57
  • It should - but I'd need to confirm I was thinking either finding something that would drop in, or good ol VHB. I'd still need to size it appropriately tho Jul 20, 2023 at 7:59
  • In a real emergency situation it may be worth setting it up with an inverter...can you rely on mains power in such a situation?
    – Huesmann
    Jul 20, 2023 at 12:26
  • In an emergency. I'm expected to seal it up. Outside an emergency removing it is fine as long as I leave most of it intact... Jul 20, 2023 at 12:30
  • As per the code "(i) Fragmentation plates (Clause 4.4) of the ventilation sleeves are allowed to be removed provided that the fragmentation plates and its bolts and nuts are mounted or kept together for use when needed. If the plate is to be mounted on the HS wall, it shall be done in accordance with Clause 7.2.1(g)." Jul 20, 2023 at 12:31

1 Answer 1


Rather than removing the plate, mounting a fan (either a duct fan or a computer fan) that fits in the duct, or mounting a box over the inner or outer end (with the outer end box covering, but not disturbing the plate so it remains functional) and that has a fan would be effective. You should only need one fan - if you blow in one hole, exhaust should blow out the other.

This is a random example of a mains-powered duct booster fan that (if you get the right size) should slip into the end of the duct:

enter image description here

Image from https://cdn1.storehippo.com/s/5c2f4c807a4c294f479436f5/5fe6d306189f3707b11c386e/31ssdygtx7l-480x480.jpg no affiliation; I've never even heard of the supplier.

Connecting a short section of duct to the inner end might provide more options for mounting a fan, such as a mixed-flow axial fan with a 125mm intake and exhaust, but a body that might be 150 or 200mm diameter.

If I make the seemingly reasonable assumption that the shelter might well serve double-duty as a pantry (you'll be with the food if you have a need to use it for the shelter purpose), fan mounting might be as simple as a shelving unit on the sidewall that has a shelf at a convenient height to support the fan at the inside of the duct.

  • The plate does provide a few convenient mounting points, and is allowed by code. I am thinking of using it as a sort of small home office. Wall mounting things is uh... Interesting but I have that as a plan B Jul 20, 2023 at 11:59
  • Oh there's a bunch of aliexpress ones that might work as a proof of concept. How I size it is part of the issue, especially buying online. I don't mind buying one or two cheap fans to test the fit and specs. What's the 'advantage' of keeping the plate on an intake fan? Jul 20, 2023 at 12:35
  • It's there if or when needed, with no time lost to screwing it back in place. But you've clarified that your code permits removing it if you keep it near the vent, if you prefer to do that. Size-wise, you need one that fits IN a 125mm duct (the pictured one appears to be "one end in, one end over") if the drawings are accurate, but might as well wait until you've moved in and can measure. There are also fans that fit fully in a duct (typically with foam rubber around the outside for a friction fit) but I didn't find a nice picture on a quick look.
    – Ecnerwal
    Jul 20, 2023 at 13:49
  • That's around september hopefully. Covid's done terrible things for construction schedules here, and I'm finally close to the point where I go "Where's my testpen? " :D Jul 20, 2023 at 13:53

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