Inspection pits, are they safe?

[gavuk]

I considered a pit when i built my garage,i was keen, had thought about using an old oil tank carefuly modifiedto form waterproof liner,perhaps from freecycle,a mate put me off by pointing out the foundation of the garage would need to be deeper or at least checked carefully to make sure pit was not undercutting or effecting the stability may require building regs or at least a proffesional structural engineer opinion ?.....i opted not to build pit.hope this helps Gav

 

[bill_gj]

I'll tell you a tale of how dangerous it can be to work in an inspection pit.

Some years ago, I was working on a bit of development that needed the odd visit to vehicle dealerships to check some fuel pumps and fuel level senders.

Two of us used to go – me and our lab technician. Normally, we'd wait for the dealer's technicians to drop the fuel tank, then do our bit and then get out of the way.

On one particular occasion, we had a colleague sent along to see what was happening for educational purposes.
This happened to be a young woman. She was no stranger to us as we knew her from another part of the organisation. She'd transferred to our place to get more experience.

Anyways – the dealership visit this time was to a bit of a backward establishment that appeared to have last been cleaned up in about 1946 and had few hoists, so our vehicle was parked over a pit. They were a bit busy and agreed to let us get on with the whole job.

Tech man and me go down pit to work on tank while new girl observes from ground level.

Now, you may be thinking, fuel tank, petrol vapour, pit filling up??
But no !! Suddenly, Tech Man accuses me of having perpetrated a severe and dastardly act of a digestive gas nature. It was foul, but wasn't me and I parried his accusation, suggesting it had been him all along.
Then we realised. Looking around for our colleague, we found she had scarpered and left us to our odious fate.
Sugar and spice and all things nice – it wasn't.

 

[rtcosic]

I have no idea about design and use of a pit for COMMERCIAL purposes, but can comment about mine for DIY purposes.


I built a pit in my previous garage. Intended to put one in this one - didn't - and have regretted it ever since.
I looked at those preformed GRP ones, nice molded in steps, prefitted lighting etc. BUT was into 4 figures for a full sized one!
Tips from my previous pit:

1. make it LONGER than the car, or the full length of the garage whichever is longer. That way you can walk down the steps into it whilst the car is over it. Scrambling through a gap at the front or rear of the car didn't appeal to me - especially if you needed to bail out in a hurry!
   
2. Check the 'lie of the land'. I knew that my land fell away towards the bottom of the garden and that there was then a near 2 metre drop to a track. So the water table must have been more than 2 metres below my garage floor. If you are in a low point already you might want to think again. If you build a waterproof 'tank' the rising water table can lift it out.
3. I dug out the hole by hand - horrible job given the compacted stones in my land! Those little mini diggers weren't available for hire in those days. Of course it would be very easy if you built the pit at the same time as the garage.
4. I made no attempt to waterproof it - I accepted it was likely to be damp and dank down there and thought I might just paint the inside with that special waterproofing 'paint'. In the event it wasn't - due to level of the water table I assume.
5. I laid a plain concrete floor about 100-150 mm thick. I ensured the level fell away at about 1:100 into one corner. I cast a sump into that corner to make 'bailing out' easier.
6. I built the walls from bricks left over from building the garage. I molded in concrete steps. I always intended to render the brick and paint everthing with white wall paint to make it more pleasant down there, but never got around to it.
7. I didn't try to mold in lighting, just used lead lights as and when required.
8. I molded in a 50mm deep, 100mm wide recess all around the edge and used 50 x 150 timber lengths to cover it. I could park a heavy car on those covers without any problem - but do NOT jack up on them.
9. I made a 'traveller' from a large section of rectangular tube - can't remember exactly but about 50mm x 100mm x 5mm I think - to fit the recess and with a flange welded on to fit down into the wall. Then I could use a bottle jack to lift the car and remove wheels.
10. Check the track of the smallest car you plan to use it with. I was playing with a Jaguar and an Alvis at the time and it was a bit heart stopping fitting a Mini over it!
11. Don't take the boards away until AFTER you have put the car over the pit! And put them back BEFORE you take it off! ALWAYS keep those boards on when not in use. Only remove the boards you need for access - just in case.

The only time I ever needed to bail it out was after using a jet washer to clean the underside of cars, which I did regularly.
Yes, spilled petrol or (most)leaking gas, LPG WILL collect in a pit - so if you have spilled any don't do any welding or use any electrical equipment until you have ventilated the garage well!
It was very useful for routine maintenance, replacing exhausts, gearbox removal etc etc. Only used it a couple of times for welding, but as I can't do overhead anyway not that helpful - but better than scrambling around on the floor. For sill/floor repairs I plan to built a rotisserie.

Worst problem?








The number of people who ask to 'just pop around for a minute' once they learn you have a pit!

 

[Rich.C]

Thanks again lads, great replies

was into 4 figures for a full sized one!

Bloomin eck!, that is more than my old bangers sitting over it are worth

Looks like a home made job as irondarren and rtcosic describe is the way to go. Should be better than working under cars on axle stands all the time.

 

[MrFluffy]

Im going to dig one when my house is finished (cant yet because the mobile home is parked where the pit will go), one great reason, I cant afford a 4 post that can lift 8 tonnes of jcb and I hate crawling under it enough to put off some outstanding jobs.
I will have to tank it, and looked at those grp pits, but I think ill cast one up with rebar and thick concrete walls with a dpm membrane on the outside of the casting. That way I can form a proper sump and cast in some conduit to carry power for a extractor fan etc. Should take about 10 mins to actually dig it

I used to use a commercial pit many years ago when working on class 1 hgv units and trailers, so itll be cast with some angle iron runners on the edge with a fair overhang, and Ill try to get some steel grates I can slide along, as you always seem to need to jack something up, and if you ever do drop something in the pit backing it on, theyre a saver to slide under the diff or something to secure it from dropping right in...
We used to weld and everything in ours, but it was 60ft long or so and only ever got diesel engined stuff over it...

 

[rtcosic]

Bloomin eck!, that is more than my old bangers sitting over it are worth

I was looking for one about 1.75m deep and 6m long though!

 

[general--lee]

i used a pit for 6 years at my last garage and i think they great, obvisouly if draining fuel tanks etc you need to clear vapour fumes etc very well but in a way i miss the pit , ramps are actually quite slow in going up and down lol!!!

my pit had a vertical ladder so like 3 steps and you was in / out so you could quickly get from bonnet area back to underneath where as with a ramp you gotta wait fot it ,

there is some jobs that are a pain on a pit but then some jobs i would prefer to use a pit but now i only have ramps BUT i would certinaly consider having another pit as well if i had room

 

[bob the builder]

Dig the hole then lay a large sheet of damp proof membrane so it covers the base and returns up the sides, must be in one piece and the very thick sheet, lay the base and start building this will keep the pit dry. A number of times we have precast panels about 400mm high and lowered them into position you will soon have it up to floor...

 

[theoss]

Don't use any propane in the building if you have a pit..