What is a heifer cow? A heifer is a mature female cow that has not calved, or given birth to a calf, yet. As soon as a heifer gives birth, she becomes a cow. A cow refers to a female of any age that has given birth.
When most people think about gas masks or respirators, what they usually envision is a tight-fitting plastic or rubber face mask with some sort of filter cartridge. The mask covers the nose and mouth. These are called half-mask air-purifying respirators.
Half Facepiece & Full Facepiece Gas Mask/Chemical Cartridge Respirators. These chemical and gas masks are also known as air-purifying respirators because they filter or clean chemical gases and particles out of the air as you breathe.