Respirators protect people from three basic health hazards: particulates, harmful gases and vapors, and oxygen deficiency.

Particulates include sand used in sandblasting and latex paint atomized during spraying. Particulates also are referred to as dust, fumes, and mists. Although they are perhaps the easiest contaminants to keep out of your lungs, they are by no means benign. Inhale too much sand during sandblasting and you risk contracting lung cancer.

Gases and vapors pose the most common respiratory hazard in painting. Prominent in this rogues' gallery are organic vapors, which typically emanate from paint solvents. An initial whiff of organic vapors might not faze you, but 20 years of the stuff can lead to a brain disorder called chronic painter's syndrome. If it doesn't kill you outright, the disorder can leave you impotent, paralyzed, or psychotic.

Oxygen deficiency is what you find in the bottom of a fuel tank that hasn't been ventilated for two years. In an oxygen-deficient atmosphere, you can lose consciousness and die in a matter of minutes.

Once you've identified the hazard, you can begin choosing your respirator.

The most common respirator is the half-mask, which can either be disposable or reusable. Disposable half-mask respirators guard against either particulates, gases and vapors, or both. In the case of the particulate respirator, you throw it away when it becomes clogged up. You pitch the half-mask respirator for gases and vapors when its special filtering element is exhausted. Usually, you'll know that has happened when you begin to smell or taste the chemical.

The so-called nuisance or comfort masks sold at the hardware store, by the way, really don't qualify as respirators. "They're strictly for sweeping the garage or mowing the grass," said Stephen Navarro, a technical service representative for 3M, a respirator manufacturer. Besides, they're not approved by the National Institute for Occupational Safety and Health (NIOSH), OSHA's think tank.

Reusable half-masks rely on disposable cartridges -- some to block out gases and vapors and others to filter out particulates. The two types of cartridges are often used in tandem. Some cartridges do double duty.

Types of Respiratory Hazard

Dusts, Fumes and Mists are often grouped together as "Particulates".

Dusts Created when solid materials are broken down into fine particles that float in the air before settling under gravity. Dusts are produced by operations such as grinding, drilling, blasting, sanding and milling.

Fumes Created whe solid materials vaporise under high heat and then condense. For example metal vapour cools and condenses into extremely small particles, with a particle size generally less than one micron in diameter. Metal fumes can come from operations such as welding, smelting and pouring of molten metal.

Mists Tiny liquid droplets formed from liquid materials by atomisation and condensation processes. For example, mists can be created by: • Spraying operations • Plating operations • Mixing and Cleaning operations

Gases Substances that are similar to air in their ability to diffuse or spread freely throughout a container or area. Examples include oxygen, carbon monoxide, carbon dioxide, nitrogen and helium.

Vapours The gaseous state of substances that are either liquids or solids at room temperature. They are formed when solids or liquids evaporate. Petroleum is an example of a liquid that evaporates easily, producing petroleum vapour. Other examples are paint thinners and degreasing solvents.

Oxygen Deficiency Occurs when the percentage of oxygen in the air falls below 19.5% (3M definition). It can be caused by chemical reaction, fire or when other chemicals displace oxygen from the air.