Today I will cover personal breathing aids, and if there is interest I can cover area/group methods later.
There are three basic types of devices that you can use to clean the air you breathe, passive and active filters and supplied-air systems.
Passive filters are the most common and range from common dust masks through industrial respirators to the military grade gas masks. Passive filters all use the power of your diaphragm and lungs to draw air through them, and can only remove things from the atmosphere before it gets to your lungs. Filters do not add or supply oxygen for you to breathe. Think of them as water filters whereas a supplied-air system is a canteen, if that helps make the difference clear.
Active filtration is any system that uses an external source of energy to move the air for you to breathe. The main advantage over passive filters is that they create a positive pressure on the inside of the mask/respirator and that is a great help in keeping pollutants out of your lungs. They also make it easier to breathe and won't make you work muscles in your abdomen that you may not realize you have. The other advantage is that since it creates a positive pressure inside the mask, you don't have to have a perfect seal between the mask and your skin. Those of us with beards can don a Powered Air Purifying Respirator (PAPR) and breathe clean air without having to shave first. (Yes, I'm trying to get the boss to buy me one.)
Supplied-air is any system that provides stored and/or piped-in clean air to an air-tight hood or mask. The typical Scuba (Self Contained Underwater Breathing Apparatus) tanks that divers use are a good example of a supplied-air system, and several companies make SCBA (remove the word underwater) gear for firefighters and separate systems for industrial use. There are also emergency hoods with a small air bottle, commonly referred to as Scram-Packs, designed to allow a person to evacuate an area with severe air quality issues. At my job, we carry them when applying anhydrous ammonia and certain pesticides, and the 10 minute air bottle is plenty to get clear of a serious leak. Self-contained means more mobile, but with a very limited amount of air -- usually no more than 30 or 60 minutes' worth.
Many industrial respirators can be converted to a supplied-air configuration by removing the filters and connecting to hoses running from a certified source of clean air. Dragging hoses around limits your mobility, but gives a much longer time to do what needs to be done. The main problem with SCBA systems is the cost of keeping the bottles full (2200 psi is a bit more than your garage compressor can handle) of clean air (oil-less compressors and big pre-filters) unless you have the budget of a business or municipality to draw upon.
Choosing the Right Type
Those are the types of breathing equipment that are available, now how do you figure out which one you need?
The first step is to identify what you are likely to run into, so you can find the mask that will protect you the best. Knowing the limits of specific chemicals is a special art that requires training, since some are dangerous at very small concentrations. Knowing what to expect will give you a chance to study ahead of time and make sure you have what you need.
If you're dealing with dust from construction, demolition, or weather, a simple dust mask will usually be enough. Look for the ones with an exhaust valve on the front; they make breathing easier and don't trap as much moisture as the unvented style. In a pinch, a wetted piece of cloth wrapped around the lower half of your face will work almost as well as a commercial dust mask. Cowboys didn't wear bandannas just to look cool; they were there to be used as dust masks when they got stuck behind the herd of cattle.
If there is lead paint or asbestos present, then you'll need to look at a respirator with filters rated for those. Half-face respirators are designed for minor-to-moderate contamination that does not pose a threat to your eyes, and are the most commonly used industrial type. Since they don't cover the entire head there are fewer problems with claustrophobia and heat stress for the wearer.
Any time you start to deal with vapors or mists (welding and cutting certain metals, chemical exposure, etc.) you will need to find a respirator with replaceable filters and then get the filters that will remove those chemicals. Most filters have a lifespan of hours or days once the factory seal is broken, and many have a shelf-life as well, so rotate your stock as needed. Additionally, if you're dealing with mists instead of dusts, you'll be looking for a full-face respirator in order to protect your eyes. Military surplus gas masks fall into this category, with the caveat of "it's surplus for a reason": natural and man-made rubbers have a definite useful life, and when they start to weather-check or crack they are no longer of any use, so be careful what you buy. Finally, face shields fog up from the moisture in your breath in cool/cold weather and you can't just take off the respirator to clean it. Cat crap (TM) is a good anti-fog treatment for goggles and face shields.
If there is a hazard that will deplete or replace the oxygen in the area you are in, or a chemical is present in concentrations that are "Immediately Dangerous to Life and Health" (IDLH, an acronym that you may see on warning labels or data sheets) then a supplied-air system is the only type that will work.
Next, you need to know how much money you have to spend on a respirator.
- Dust mask: a couple of dollars apiece.
- Half-mask respirator: $20-50, plus filters.
- Full-face respirator: $30-100, plus filters.
- PAPR: $1500-2000, plus filters (usually more than 2) and batteries.
- SCBA: $800-5000, plus a way to refill tanks.
Finally, you need to make sure you know how to use what you are looking to buy. If you are ever offered a chance to take Haz-Mat or Haz-Com training, do it. Learn how to fit a mask, as even the simple dust masks need to be fitted to you face in order to do any good. Find someone who can show you how to put on and take off the respirator you've chosen; there are tricks that make is a lot easier and save wear and tear on your equipment. Unless you are trained, I would suggest you avoid the SCBA systems, as there is far too much potential for making lethal errors.
For liability reasons, I can't tell you what you'll need for any specific hazard. Do your research and if you have a specific question about a specific hazard, I may be able to point you towards where you can find the information. I'm a trained user but not a trainer, so I don't have all of the information you may need for your personal preparations.