From DIYinfo.org
Not all respirators provide the same protection against harmful vapours.
Spraying or not, a respirator is a great safety measure for your lungs. Even when spraying seemingly benign water-based products, we strongly recommend a respirator and good air circulation.
When it comes to finishing materials and solvents, the sad truth is that using almost any of these products can be dangerous. The risk ranges from slightly hazardous to extremely toxic, and precautions against them should include skin protection, eye protection and lung protection.
Gloves and goggles aren't all that hard to find or fit properly, but respirators can be a different story. Not all respirators provide adequate protection for woodworking finishes and solvents, and a poor fit may make even a suitable respirator inadequate. Here I'll look at the types of respirators to wear when using finishes and solvents in the average home or small shop. Particulates, such as sawdust, require a different type of respirator. Also, professionals using extremely hazardous materials, or having prolonged exposure to chemicals and solvents, will require more sophisticated respirators.
You may not need a respirator for every type of finishing method or product. Brushing or wiping many finishes with adequate ventilation may be safe when using shellac, oils (linseed and tung) and some water-based finishes. However, once you start getting into acutely toxic solvent-based finishes like lacquers and varnishes, a respirator is a good idea.
When atomising or spraying any finish, including seemingly benign water-based finishes, I strongly advise using a respirator and providing good air circulation.
[edit] Most respirators have two layers of protection
Many respirators come with a pre-filter in front of the charcoal filter canister (see Inside a respirator's cartridge). The pre-filter captures larger particles, such as pigments and dust, preventing them from clogging up the charcoal filter and reducing its effectiveness. Expect to go through several pre-filters before replacing the cartridges. When I order a matched set of cartridges, I order three sets of pre-filters.
Most respirators use activated carbon to filter harmful vapours because it has a very large surface area and chemically attracts organic vapour and gas like a sponge.
The charcoal canister eventually becomes saturated and the cartridge needs to be replaced. Knowing when to do this is difficult, because the type of use and conditions affect the service life of the filter. If you can smell the solvent or finish, replace the cartridge. As you get used to the service life of your respirator, you can replace it on a regular basis. The charcoal filter is always working—whether you are wearing it or not. You can extend the life of the filter substantially by storing the cartridge in a sealed plastic bag.
[edit] Look for the right kind of cartridge
The cartridge for most finishing situations should be rated for organic vapours and gases, paints, lacquers and enamels. Respirators with these cartridges are available at just about all paint stores and large hardware stores.
If you have a special requirement or are unsure whether the respirator will work with the finish you're using, get a copy of the material safety data sheet (MSDS) from the manufacturer or supplier of the finish and send it to the respirator company, which can match the cartridge to the respirator. Or check the yellow pages for you’re nearest safety equipment & accessories store.
Cartridges rated for organic gas and vapours, paint, lacquer and enamels do not offer suitable protection for the following materials: ammonia, as when fuming wood; methylene chloride found in some furniture strippers; methanol found in some wood stains and finishes; two-part urethane finishes whose odourless compounds cannot be detected if the respirator does not fit properly or if the charcoal cartridge is saturated. For these situations, you should contact the manufacturer of the product or the yellow pages for you’re nearest safety equipment & accessories store to get specific recommendations.
[edit] What respirator is right for you?
Respirators that protect against vapours are divided into two classes: some work on negative pressure, and the others work on positive pressure (see Two methods of protection).
Two methods of protection:
Negative-pressure respirators typically have a flexible face piece made from neoprene or silicone and incorporate the cartridges and pre-filters. Neoprene provides the best chemical-resistant seal, while silicone is a bit smoother and may be more comfortable for some users. These respirators mount securely over your mouth and nose, allowing you to breathe only filtered air. Designs available include disposable versions, where the entire respirator is thrown away when the cartridge is saturated. Models with replaceable cartridges and pre-filters can be half mask or full mask, the latter providing eye protection as well.
Positive-pressure systems, also known as air-supplied systems, pump clean, breathable air into a mask or hood. The air can either be filtered air (using a filtering system similar to the charcoal cartridge), or the air-hose inlet can be located away from the finishing area in a source of fresh air.
A negative-pressure respirator is the most economical and popular form of protection, while positive-pressure systems are more expensive. The main difference between the two is the level of protection. A negative-pressure respirator with a half face mask, regardless of the manufacturer, can allow around 10% of contaminated air through. A full-face mask allows 2% through. A positive-pressure respirator allows less than one tenth of 1% (0.1%) through. Over extended periods of use, say four to eight hours, this is a sizable difference in protection.
These comparisons assume that the respirator has been properly fitted to the user. The Occupational Safety and Health Administration (OSHA), which monitors industrial workplace safety, will not allow masks on individuals who have facial hair or glasses that extend beyond the sealing area of the mask. A hood is the only answer for these individuals.
Even if you are clean-shaven and don't wear glasses, you should still be concerned about the proper fit of a mask-style respirator. Perform a few simple tests (see Testing for proper fit), adjusting the straps as necessary.
[edit] Test for a proper fit
1. Cover the inlet holes where the cartridges are placed and breath in. The mask should collapse slightly.
2. Then cover the exhalation vent and breath out. The mask bulges slightly. If all of the above occurs the mask is a good fit.
For most woodworkers, a negative-pressure respirator is adequate when use is limited to 30 minutes. A half-mask, dual-cartridge style with elastic straps is the most practical. If you want the best protection, or have prolonged exposure to solvents and finishes, take a serious look at a positive-pressure respirator (a battery-operated version is the most cost effective).
In all cases, remember that a respirator is no substitute for doing your finishing in a well-ventilated area.
