As more research is being done on the chronic effects of low level exposures to pesticides, it continues to be apparent that pesticide use can adversely affect the health of the pesticide applicator. That's why it's important that people wear the appropriate personal protective equipment, and even use more PPE than is required, especially when treating Christmas trees with a high pressure sprayer.
One of these pieces of equipment is the respirator. In my opinion, anyone treating trees with a high pressure sprayer should use a respirator. This is true whether you are using horticultural oil or a synthetic pesticide. Few materials require the use of a respirator on the label, but since you are continually walking through the spray, that is the best way to reduce exposure.
Some of the commercial applicators have purchased the helmets with motorized forced air which completely cover the head. These offer the most protection, and are the easiest to wear. They keep the worker cool, and don't require a lot of effort to breath through them.
But a lot of people still depend on either the full or 1/2 face respirator with attached cartridges which are certainly less expensive. However, there are several issues with these.
1. They don't cover the entire face, and in fact the ear canal is one area of skin that is particularly thin and will readily absorb pesticides. The rate of absorption is far higher than the skin on your palm or forearm. Using a hood on a spray suit will eliminate this problem.
2. Many people don't fit the respirator closely enough to the face. I've seen several folks wear respirators that just hang on their face. The respirator is supposed to fit snugly so that all air breathed in passes through the cartridges. And yes, when you do this, they will fog up. But, when the fit isn't snug, contaminated air can come in through the sides. If a man has a beard or mustache, this can interfere with the fit. In fact, it is best not to have facial hair when using a respirator.
3. The third issue then becomes one of applicator's health. Some people's lungs just aren't strong enough to pull air through the respirators.We all know how tiring it is to wear a hot spray suit and respirator and walk through trees spraying with a hose. You have to have good heart and lungs to be able to do this demanding work.
In fact, OSHA regulation 1910.134 requires workers be properly trained in using a respirator, that a fit test be conducted, and that the worker is certified by a doctor as being physically fit enough to use the respirator. These requirements have largely been overlooked in agricultural circles, but that may be changing.
So be safe. Check the fit on your respirator, and use it like it was intended.