Air fed masks and compressors

[elese]

Hi

I have some painting on a narrowboat to do in 2 or 3 months, hopefully.

Stone chip compound on the hull with 2-pack epoxy over the top, and 2-pack epoxy everywhere else, including inside the boat.

I am reading about paint safety on this forum and thinking about an air-fed mask, particularly for painting inside the boat, as fumes can be strong even with all windows/doors open.

I understand that air-fed masks should have a clean air source away from the paint, generally fed from air compressors. Are there any air-fed masks that do not need an air compressor (say, powered by mains electricity, and drawing air from a tube from somewhere clean?) Is there such a thing?

Thanks

 

[Barking Mat]

There's at least one for sale on here.

 

[julianf]

Hi

I have some painting on a narrowboat to do in 2 or 3 months, hopefully.

Stone chip compound on the hull with 2-pack epoxy over the top, and 2-pack epoxy everywhere else, including inside the boat.

I am reading about paint safety on this forum and thinking about an air-fed mask, particularly for painting inside the boat, as fumes can be strong even with all windows/doors open.

I understand that air-fed masks should have a clean air source away from the paint, generally fed from air compressors. Are there any air-fed masks that do not need an air compressor (say, powered by mains electricity, and drawing air from a tube from somewhere clean?) Is there such a thing?

Thanks

I looked at this a while back and could not find any.

There are welding masks with belt packs, but you're still breathing local air then.

I guess to get sufficient flow at low pressure the feed tube would need to be impractically wide bore.

They may exist. But, like I say, I didn't find any.

 

[jo1010]

Painting 2 pack in enclosed spaces with no extraction is a big problem. To do what your thinking of would need a lot of air extraction - look at auto body paint booths with all the downdraft ventilation they have for an idea of what's needed. No mask (either air fed or cartridge) is gonna protect you in an environment thick with paint mist. You have to solve the air movement problem first, but how?

 

[julianf]

Painting 2 pack in enclosed spaces with no extraction is a big problem. To do what your thinking of would need a lot of air extraction - look at auto body paint booths with all the downdraft ventilation they have for an idea of what's needed. No mask (either air fed or cartridge) is gonna protect you in an environment thick with paint mist. You have to solve the air movement problem first, but how?

The op isn't asking about extraction. It seems like they know the dangers but are just looking for an air fed mask that runs on a low pressure (remote) air feed rather than a compressor.

 

[Jelly_Sheffield]

Hi

I have some painting on a narrowboat to do in 2 or 3 months, hopefully.

Stone chip compound on the hull with 2-pack epoxy over the top, and 2-pack epoxy everywhere else, including inside the boat.

I am reading about paint safety on this forum and thinking about an air-fed mask, particularly for painting inside the boat, as fumes can be strong even with all windows/doors open.

I understand that air-fed masks should have a clean air source away from the paint, generally fed from air compressors. Are there any air-fed masks that do not need an air compressor (say, powered by mains electricity, and drawing air from a tube from somewhere clean?) Is there such a thing?

Thanks

What you're looking for is called a "Fresh Air Breathing Hose Respirator"

The MSA Turbo Flo is the most common model, and can be used with a fan assisted unit for upto 18M hoses, or just the hose for up to 9M

Used correctly, a properly fitting full-face mask connected to a unit of this type has an assigned protection factor (APF) of 40, which is considered to be the minimum required level of protection for spraying isocyanates.

However the HSE recommends in addition to a minimum of APF40, that only constant flow or positive pressure demand supplied air RPE with a low flow indicator is used for spraying isocyanates, so you should only consider using this kind of system in fan assisted mode, and only if there's a flow indicator on your mask setup...

I think a Fresh Air Breathing Tube system would probably still be considered "marginal" at best for your purposes by most RPE professionals... @Parm can probably give the official line on this.

You should also consider the ergonomics, specifically potential for the hose to get squashed by working in awkward positions or stuff falling on it restricting your air supply, whereas a compressed air system is much less likely to be cut off by this.

 

[Jelly_Sheffield]

No mask (either air fed or cartridge) is gonna protect you in an environment thick with paint mist.

In general you are correct in the approach that "engineering controls" like ventilation should always come first...

But a properly fitted positive pressure air fed full-face mask (of the type recommended for Isocyanate Spraying) can effectively protect people from Oxygen Deficient or other "Immediately Dangerous to Life and Health" (although is required to have an escape bottle as backup in such scenarios).

One of my old clients used them to protect workers entering "Cyanide Booths" (containment structures constructed to prevent the spread of cyanide gas around the plant in case of accidental release during maintenance) with no problems... Somewhat more consequential than 2-Pack Spraying.

 

[ajlelectronics]

2-pack epoxy over the top, and 2-pack epoxy everywhere else,

Not Iscocyanate hardener.

 

[Parm]

When spraying solvent based paints inside a boat which is essentially a confined space, APF on RPE goes out of the window essentially as your primary hazard is that of explosion from solvent based fume build up

On any job like this its vital that you have additional ventilation to remove paint mist build up from the confined space to prevent fire and explosion risk

If your using an epoxy based product then it wont or shouldn't contain isocyanates. Check the MSDS or drop me a PM with the details.

As for RPE, my recommendation is air supplied respirator, fed from a compressor set up to supply breathing air and located away from where you are doing the work

 

[elese]

Thanks to everyone, all useful information. I know little about this so I wanted to make sure I was getting the right thing.

I'll have to look whether it is easier and cheaper to get a Fresh Air hose Respirator, or perhaps see if I can convince someone to let me borrow their air compressor.

Prices seem variable, with second-hand masks about £100-200 and airflow pumps about £150. New airflow systems seem about £600+. I was hoping to get something just used a few times on ebay, same as I will. I wonder if you can rent them, though if it's for more than a couple of weeks, buying used and selling on is usually cheaper, providing it is good condition.

Is something like this suitable?

Pardon our interruption...

When spraying solvent based paints inside a boat which is essentially a confined space, APF on RPE goes out of the window essentially as your primary hazard is that of explosion from solvent based fume build up

On any job like this its vital that you have additional ventilation to remove paint mist build up from the confined space to prevent fire and explosion risk

If your using an epoxy based product then it wont or shouldn't contain isocyanates. Check the MSDS or drop me a PM with the details.

As for RPE, my recommendation is air supplied respirator, fed from a compressor set up to supply breathing air and located away from where you are doing the work

The fire risk is something I hadn't give much thought to, especially as it is now within a tent, and not just outdoors. I will look to roll back all the panels when painting, but not sure if can be done for the roof.

It does have more windows than most boats, of course all open.

The paint is Jotamastic 90, for which the safety sheet lists 'flammable liquid and vapour' as a hazard, and Carboline Rustbond NG FC, which does not. Isocynates are not mentioned as hazardous ingredients, though they both have benzenes listed (which I remember from Chemistry in school) and other chemicals I have not heard of.

Do you have any information on how to work out level of air extraction needed?

Cheers

 

[Jelly_Sheffield]

Do you have any information on how to work out level of air extraction needed?

There is a rule of thumb that an area is more or less "safe" when the concentration of flammable vapours is less than 10% of the lower explosive limit.

You can use this to estimate the airflow requirement based on the rate of contaminant discharge.



The solvent in your paint is a mixture of Xylene and Ethylbenzene, which have Lower Explosive Limits of 0.9% and 0.8% respectively... So your "10% of LEL" target would be no more than 0.08% solvent in air.

Assuming you don't require additional thinners*, part A of your product is approximately 17% solvent, and part B of your product is approximately 5% solvent.

*(If you do use thinners, you need to redo the maths based on how much additional solvent is in the paint).

The mix ratio is 3.5:1, so ((3.5×17)+5)÷4.5 gives a solvent content of about 14.3%

So for every kilo of paint sprayed you are putting 143g of solvent into the air...

The TDS advises a maximum application rate of 2.6L/minute and the bulk density is near enough 1kg/L so you will be putting out upto 2.6×143 = 371.8g of solvent per minute...

So you need enough airflow to dilute 372g of solvent to 0.08% in air... 372÷(0.08÷100) = 464750g of air needed to dilute it.

Air has a pretty low density of 1.2kg/m³, so if you need 464.75kg of air per minute, you need 464.75÷1.2 = 387.4m³ of air per minute.

Fan are generally rated in m³/hr or cfm... So you would need to multiply by sixty, giving 387.4 × 60 = 23237.5 m³/hr (times by 0.59 to give cfm)



This is somewhat impractical for a temporary DIY setup:

- Firstly, that kind of airflow requires a literal wind machine, or three to four 20" industrial ventilator fans... So you won't see much change from two grand regardless of if you buy or hire them.

- Secondly, passing that airflow through a narrow boat with a cross section of around 4m², would result in a "wind speed" of 1.6m/s (3.6 mph), which is probably tolerable for spraying, but is going to be perceptible, and potentially problematic around any areas where there's a change shape causing turbulence.



For practicality's sake you would probably have to either:

1) relax the 10% of LEL guideline, and aim for not exceeding 80% of the LEL (to account for the fact that you're not always going to get perfect ventilation, but you do want to remain below LEL at all times)

This would result in an airflow requirement just shy of 3000m³/hr, so (assuming a ventilation efficiency of 50% to be on the safe side, as you have already reduced your margin of safety because relaxing the LEL limit) two of the 12" ducted "ventilator" fans sold by machine mart would do the trick, at around £400 to buy.


2) Reduce the application rate below the maximum specified in the TDS...

2.6L/min is very high for paint spraying and is presumably appropriate for users who need to cover huge areas quickly, because they are painting literal ships in drydock.

A rate more like 0.25L/min would be the upper end of a normal handheld spray gun, which would reduce the airflow requirement to around 2300m³/hr.

At that point you may get away with just one of the big machine-mart ventilators, assuming you are using plastic sheeting to seal the ventilator to one end of the boat, to ensuring most the airflow is passing through.

 

[jo1010]

^^comprehensive analysis this shows the kind of kit needed to achieve proper ventilation in enclosed spaces - it works out very expensive for a one off job.
I'd be considering brush on solutions rather than spray in that situation

 

[elese]

^^comprehensive analysis this shows the kind of kit needed to achieve proper ventilation in enclosed spaces - it works out very expensive for a one off job.
I'd be considering brush on solutions rather than spray in that situation

Yes, looks I like will be using a brush. Specification for both paints above does include it