DIY Supplied air respirator

[SPF]

Hi everyone,
I have a number of projects on the go, which include welding some smokey horrible material, and painting with 2k paint.

Consequently I have decided to look at supplied air respirators. I have checked out the models readily available in Australia and am amazed out how delicate they are, and how much cost is involved with keeping them in working condition. So, I'm now looking at making a DIY version with readily available parts that I can replace when I either burn a hole through them or cover them in paint (ie the face mask). My view is that well maintained DIY PPE is going to be better than patched/repaired systems that are too expensive to keep spares on hand.

So my question is have any of you built your own supplied air respirator/system, and if so would you recommend your setup? If you're happy with what you have, please share some details.

At the moment I'm looking at constructing a system out of the following components:

1. A disposable painting hood/full face shield/helmet and visor - and to be honest I may set up different options for welding and painting;
2. A small side channel blower (as used for many industrial purposes and for aquaculture air supply); and
3. Some corrugated CPAP hose, which is made of silicone so it is more resistant to weld spatter than the corrugated PP/PU hose.

After looking around at the various pump/blower options the side channel blowers look like a good option as the air does not pass over the electric motor, and the bearings are mounted externally to the casing, so there is no opportunity for contaminating the air with oil or grease. I'd like to know if anyone has other options they'd recommend.

I'm well aware of the hazards that I'm trying to avoid by using the supplied air respirator, so don't feel the need to fill this thread with warnings about isocyanates and various welding fumes. With that said if any of the PPE you have used have a tendency to catch on fire from welding spatter, or dissolve when exposed to paint solvent, then please let me know.

Thanks in advance.

[BobL]

In terms of the hierarchy of control, a well established and professionally accepted system of OHS, PPE should be the last choice after all other things are done to remove or reduce the H&S problem.
This is why I don't advocate the use of masks for wood or any other dusts, let alone trying to DIY on masks etc.

Another reason for not DIY on masks is that most DIYer don't have the ability to adequately test their efforts.
Even though I have access to some dust testing gear I have found testing masks to be very difficult, because they end up having to be fitted to an awkward shape i.e. a human being.
Besides even professionally made masks still leave the fume and sprays inside a shed which ends up making a real mess.

All this is why I think it is far better to put one efforts into physical removal of the fumes/dust/spray etc at source by using a fume hood / extractor.
For a variety of reason,s conventional DCs that use filters are not appropriate for fumes or sprays but simple fume hoods that extract air outside are.

Its pretty easy to make a small fume hood/booth and fit the hood booth with a powerful enough motor/fan to suck enough air so as to remove the fumes.
This is why I have in my shed. Its a 1/3rd HP squirrel cage fan that draws up to 1600 CFM.
The last photo shows the old (RHS) and new (LHS) motor/fans
Fumehood12.jpgFumehood10.jpgFumehood9.jpgCombo.jpg

As you can see the booth is used for small spray jobs as well as welding
I can weld Zn coated steel under this hood and not detect any ZnO particles in the shed air when I do this.
Because I can enclose the booth right down using the bifolding doors I don't get over spray on anything else in the shed.
I also have a HEPA room air filter that I can turn on before I spray that cleans the air up inside the shed.
Then when I paint there is much less dust settling onto the painted objects.

For a bigger booth, a tent or plastic sided enclosure can be used.
We are in the process of doing this at our mens shed using a pop up gazebo to which an extractor will be added.
I only just made the hood for the extractor a couple of days ago.
Its made out of the galv sheet from the backs of old appliances and will be covered with some coarse filter media to entrap the overspray.
The 600 CFM extractor comes from a skip at work - it had a 3P motor on it which I replaced with a washing machine motor.
IMG_1582.jpgIMG_1583.jpg

Of course booths and hoods cost more than a respirator but having used a respirator in the past (and I still do occasionally) I think it's a lot more comfortable and definitely safer using a fume hood/booth.

[SPF]

Hey BobL,
Thanks for the reply. Nice set up too.

I totally agree with you about removing the hazard rather than using PPE. In these projects I can't completely remove the hazards, and they are not being done in the workshop, so PPE it is. I'm not going to be in a IDLH situation and if the air stops i can walk/roll out of the hazard zone.

I am looking at the supplied air respirators because I have a beard, and there is less testing required to ensure a satisfactory result. You don't have to ensure that there is a good seal, and the systems work on basic principles of pressure differentials. There are a few problems that people generally don't know about relating to backflow and cavitation but these are all manageable if sufficient throttles are put in place and air velocity and direction are controlled.

[BobL]

I am looking at the supplied air respirators because I have a beard, and there is less testing required to ensure a satisfactory result. You don't have to ensure that there is a good seal, and the systems work on basic principles of pressure differentials. There are a few problems that people generally don't know about relating to backflow and cavitation but these are all manageable if sufficient throttles are put in place and air velocity and direction are controlled.

I too have a beard and a respirator, a full face/mask Triton which I use in the circumstances you describe.
However, it's inappropriate for welding and even painting.
I wear it when working outside with things like an Arbortech or a chainsaw in really dry wood, and it's excellent for attacking wasps nests otherwise I find it and all respirators too claustrophobic and too hot.
The other thing I dislike is being tethered to things like air lines.

I did measure the Triton flow rate back in July this year,
The flow rate for two P2 cartridges in parallel is 2.9 L/s or 174 L/min.

This rate is OK indoors on a cool day when not working too hard.
However. on a warm or hot day, or when one had to do something moderately physical, I don't think it's sufficient and would want to double that flow.
300 L/min is 10 CFM which is a big ask for a small pump if it has to push air though filters.
Of course you can opt for using air lines and a bigger pump somewhere but that takes you back to a tethered situation..

At work we used respirators tethered to a dedicated 3P - 3HP compressor and fancy filter .
I used to run my respirator on max flow so the compressor used to cycle a lot during its use.

[SPF]

Thanks for that BobL, yeah I'm working on the basis of 300LPM at the mask, so with resistance from the hose and other inefficiencies I'm looking at a 450 LPM pump. Because of the limited requirement for pressure, the side channel blowers are far more efficient than a compressor to do this job. Apparently the best results can be obtained putting the filters on the vacuum side of the pump, but I'll test this. I'm willing to deal with being tethered to the pump, as i will only need to use the system for limited time - unfortunately, I will need a long hose which will no doubt be a PITA.

[soundman]

one of the big advantages of a supplied air respirator is that the air intake can be located some distance away from the contaminated area.

The other big advantage is that the pump and filter pack can be as bulky as you like.

Yeh I know the establishment types will poo poo DIY PPE ...... but if you know what you are doing you should be able to achieve better results than you could buy at any price.

ahving the filtration on the intake side of the pump is a no brainer as long as you can obtain a clean pump/fan ....because most of the commonly available filter packs are intake filters.

One thing that will be an issue will be the intake restriction of the filters and the pumps suction capacity.

Most centrifical blowers the motor and bearings are outside the air path ....... there are also some centrifical blowers specifically designed for food applications which might be suitable.

cheers