Spray booth set up....


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Established Member
22 Aug 2009
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Another topic in many ways closely related to the dust system issue! I'm planning (but not necessarily going to immediately install) a DIY spray booth of about 4.5 X 2.5 X 2.5m high.

I've done some custom painting of motorcycles, and hope to use some of these techniques on art(ish) pieces - so that while i will be using furniture finishes a lot of the time i may occasionally get into the automotive/furniture two pack space - albeit in tiny volumes.

I searched the site, but couldn't quite get at the issues i seem to be unearthing. To share some information first:

As usual it started out simple, but got more complicated with investigation. The problem is basically that if you propose to use two pack or water based paints containing isocyanates (the cure system in many tough polyurethane acrylics, and also in automotive paints) you need a good booth.

Much like wood dust isocyanates get distributed in ultra fine sub micron particles your lungs can't handle, and cause lots of asthma and occasional cancers. Use of solvents introduces a fire risk.

There's quite a lot of info on the HSE site on the topic (the focus is more on car type booths and isocyanates), but as in wood dust it all gets blurry in the domestic/private situation, and where the qty of paint used is low. (below 0.5 tonnes of paint per annum requires no environmental licensing here, but that may vary with your local authority) Automotive booths are regulated differently to industrial booths too, even though the issues can the the same.

Basic furniture/industrial practice seems to be to use an open sided booth, with a filter panel and exhaust fan. The issues there are that (a) nothing stops dirt and dust being drawn into the both, and (b) nothing stops the fumes escaping into the broader workplace. The latter is a no-no with isocyanates where other employees are involved. Practices in the furniture, industrial and automotive areas don't seem to have really got harmonised yet.

The best type of booth seems to be a downdraft enclosed type. Air is pushed into the booth through ceiling mounted filter panels, and drawn out through more filter panels under a mesh floor.

The present regs require (and may be about to toughen up more) in the case of an industrial booth that the particles exhausted are less than 10 microns, and at 50mg/m3 of air which means filters are needed. (10mg/m3 for an automotive booth)

The exhaust must be at least 8m above ground, with other stipulations regarding buildings close by.

Auto booths must be fully enclosed to stop outwards leakage, deliver at least 4 air changes/min or a face velocity of air movement of 100 - 150ft/min (0.5m/sec) (its not clear how these numbers fit together as the latter implies much larger airflows than the former), contain any internal fire for 30min, be fitted with explosion relief panels, and with two emergency doors with the main doors.

If heated then fresh air make up must be at least 10%. The booth is subject to smoke testing to prove effective clearance (it's quite difficult to avoid creating dead zones in a booth), and must be operated and maintained in accordance with various rules. The most basic are the maintenance of a low negative pressure inside to contain fumes, and regular testing to ensure the filters are not blocked.

All of this requires planning permission, at least in the industrial/automotive repair scenario. It's not clear what the 'private' situation may be.

The basic from the operator's point of view is that the booth is to protect the rest of the workforce and the environment, and to create a clean painting environment - he/she needs a good air fed mask (to the right standards - see last nights posts on this topic on dust) and a HVLP gun - plus proper clothing.

The thinking at this stage is to build a closed booth using fire resistant Gyproc plasterboard of whatever grade on metal studs, with ceiling and floor filters from automotive spray booth type off the roll filter fabrics on steel mesh. What's proving a bit more difficult to figure out are the issues of legality (for one man use), fan sizing and sourcing (see below), likely impact on (commercial and house) insurance and paint/solvent storage. (how - in booth?) I'd hope to match best practices in terms of safety and performance.

On fan sizing and sourcing. Any fan on the exhaust size should be explosion proof. Belt drive tube axial (carefully chosen) or BC centrifugal cabinet types seem to be the usual usage - you basically need something that will not loose too much volume as the filters start to blind up and the pressure drop increases. Performance should be maintained it seems up to something a bit over 1 in WG total pressure drop in the ducting and filters.

On size around 20,000cfm is needed at whatever resistance to give 100ft/min face velocity at my proposed booth size. About half that gives 4 air changes per minute at my booth size - this equates to something between 1.7 and 4kW depending on the fan type/efficiency.

To the questions.

Does anybody have any idea how all of these considerations come together to determine requirements at the level of legalities/insurance/hassle from the powers that be for a one man/low usage/non automotive operation?

Fans and explosion proof fluorescents get expensive if you buy new. Does anybody have any ideas on sourcing on the cheap?

Has anybody any experience of fires or other accidents caused by spray booths? (i've known people to spray around gas fired tube heaters with no extraction and get away with it)

I've very little experience of spray type wood and furniture finishes. Setting aside the automotive type finishes does anybody have any idea what the types likely to be required are? Is it possible to avoid solvent based/catalysed lacquers for example in favour of water based finishes? (the latter may still contain isocycanates)

Anything else that comes to mind?

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