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.
There is now a Elevation Training Mask 2.0) is a gas mask that you place over your face that restricts the amount of oxygen you can breathe. It comes with three different nose pieces (yellow, orange and red) that you attach to the front of the mask that restricts the oxygen intake.