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.
Put your mask on immediately and leave it on. You should put your mask on at the earliest sign of danger. Also, you should leave your gas mask until instructed that it is safe to remove it. If you take it off you could risk breathing in harmful chemicals that can cause sickness, cancer, or death.