[citation needed] Airborne toxic materials may be gaseous (for example, chlorine or mustard gas), or particulates (such as biological agents).

According to Popular Mechanics, "The common sponge was used in ancient Greece as a gas mask..."[2] In 1785, Jean-François Pilâtre de Rozier invented a respirator.

Primitive respirator examples were used by miners and introduced by Alexander von Humboldt in 1799, when he worked as a mining engineer in Prussia.

It was a simple device consisting of a cotton hood with two hoses which hung down to the floor, allowing the wearer to breathe the safer air found there.

The German army successfully used poison gas for the first time against Allied troops at the Second Battle of Ypres, Belgium on April 22, 1915.

In summer and autumn 1915, Edward Harrison, Bertram Lambert and John Sadd developed the Large Box Respirator.

[17][better source needed] This canister gas mask had a tin can containing the absorbent materials by a hose and began to be issued in February 1916.

[citation needed] In the first gas masks of World War I, it was initially found that wood charcoal was a good absorbent of poison gases.

[18] The first effective filtering activated charcoal gas mask in the world was invented in 1915 by Russian chemist Nikolay Zelinsky.

[20] Other gas masks were developed during World War I and the time following for horses in the various mounted units that operated near the front lines.

[23] It was made of plastic and rubber-like material that greatly reduced the weight and bulk compared to World War I gas masks, and fitted the user's face more snugly and comfortably.

[citation needed] Although thorough training and the availability of gas masks and other protective equipment can nullify the casualty-causing effects of an attack by chemical agents, troops who are forced to operate in full protective gear are less efficient in completing tasks, tire easily, and may be affected psychologically by the threat of attack by those weapons.

During the Cold War, it was seen as inevitable that there would be a constant NBC threat on the battlefield and so troops needed protection in which they could remain fully functional; thus, protective gear and especially gas masks have evolved to incorporate innovations in terms of increasing user comfort and compatibility with other equipment (from drinking devices to artificial respiration tubes, to communications systems etc.).

During the Iran–Iraq War (1980–88), Iraq developed its chemical weapons program with the help of European countries such as Germany and France[24] and used them in a large scale against Iranians and Iraqi Kurds.

As late as 1986, Iranian diplomats still travelled in Europe to buy active charcoal and models of filters to produce defensive gear domestically.

While this method can be effective at trapping particulates produced by combustion, it does not filter out harmful gases which may be toxic or which displace the oxygen required for survival.

The US C2 canister (black) contains hexavalent chromium; studies by the U.S. Army Chemical Corps found that the level in the filter was acceptable, but suggest caution when using, as it is a carcinogen.

Thus, when handling asphyxiants, or when ventilation is poor or the hazards are unknown, filtration is not possible and air must be supplied (with a SCBA system) from a pressurized bottle as in scuba diving.

In the military, teargases such as CN, CS, and stannic chloride in a chamber may be used to give the users confidence in the efficacy of the mask.

The wearer of a typical gas mask must exert extra effort to breathe, and some of the exhaled air is re-inhaled due to the dead space between the facepiece and the user's face.

This method of separation will use some form of generally reactive substance (for example an acid) coating or supported by some solid material.

Though it was crude, the hypo helmet was a stopgap measure for British troops in the trenches that offered at least some protection during a gas attack.