A mask protecting its wearer from poison gas is called a gas mask. A gas mask basically filters inhaled air. These masks are also referred to as respirators.
A typical gas mask has a mouth piece (with a filter), two eye pieces and a face cover. The face cover handles the exhaled air. Purpose of the filter is to clean the inhaled air.
They have become very important in the current world due to a constant threat of chemical warfare.
The filters use different techniques for cleaning the air.
This technique uses the principle that toxic gases are more reactive than ordinary air. Hence we need a reactive chemical to react and neutralize the poisonous gas. For this purpose resins are used, resins are created by mixing atoms from different functional groups. When a poisonous gas is passed through filter containing a layer of resins, the gas particles react with resins to form some other harmless material. Hence the toxic gas gets replaced, as the name suggests.
In this technique hazardous contents from the inhaled air are absorbed while passing through a filter. This technique is useful for both harmful particles and poison gas. In some cases air is cleaned through a chemical reaction while in other cases attraction from oppositely charged particles of substrate can do the work. Elements that are used as substrates include zeolites and activated carbon.
Gas masks are available in a variety of shapes or wearing styles and can be categorized as half-face and full-face masks. Half-face masks cover only your mount, leaving your eyes and other sensitive parts uncovered, providing only partial protection to your face. Full-face masks provide protection to the entire face. They contain clear eye pieces so that the wearers visibility is not affected.
This spy prefers full face. Safety first!
These gas masks rely on a filter for air cleaning. In these masks a wearer has to inhale through a mouth piece containing a filter. Although these masks are simple, less costly and clean the incoming air effectively, they have certain disadvantages. One major threat is air leakages, which render the mask useless, because air comes in without any purification at all. Such leaks are caused when there's a hole or if the mask doesn't fit properly on the wearers face. The filter can also wear off. The toxic materials left in the filters may block the air passage through the filter.
Furthermore the filter may run out of chemicals that help in neutralizing toxic gases and particles. In such cases, the mask, or at least its filter needs to be replaced. Another major disadvantage of filter-based masks is that there is a variety of different poisonous gases and materials, such masks cannot provide protection from all sorts of poisonous materials.
These masks come with a battery-operated canister along with a filter. Basic principle in these masks is that a fan on the canister pumps in air, air is passed through a filter and gets purified. The air is then passed to the wearer through a hose. The main advantage of this type of mask is that in case of any leakage, already purified air in canister gets inhaled by the wearer rather than the contaminated air. These masks are extremely useful for infants. The major disadvantages of this type of masks include battery problems and wearing of filters much early.
This category of masks contains a cylinder filled with oxygen or a mixture of atmospheric gases including oxygen. In such masks a small tube connects the mask to a cylinder. Quantity of oxygen delivered to the wearer is controlled by a valve, also known as a regulator. Oxygen masks are used by pilots flying at high altitudes. Plastic oxygen masks are also used in hospitals for oxygen therapy.
As oxygen breathing can be dangerous near a fire, so firefighters use SCBA (Self Contained Breathing Apparatus). In SCBA a cylinder containing a mixture of oxygen and other gases is used. Similar air cylinder is also used by SCUBA (the Underwater variety) divers. The major cons of this system include its expensive and bulky nature. SCBA also contains air supply for a limited period of time.
It is interesting to note that during the World War II, British government believed that a poisonous gas could be used by enemy against civilian population. As a precautionary measure the government issued 38 million gas masks. There were three types of masks to suite different age groups. Gas helmets were designed for infants. Adults were issued black gas masks and children were provided with Micky Mouse masks. The Mickey Mouse masks had eye pieces and ears resembling the famous cartoon character, Mickey.
The main purpose for selecting this design for children was they don't get scared from an awkward looking mask, and wear the mask joyfully.