Some of London's telephone operators and engineers, trying out their gas masks at the anti-gas civilian training centre in Gloucester, where they were taught how to deal with gas attacks. (Photo by Harry Todd/Fox Photos/Getty Images). 13th February 1937

Soldiers use electronic sensors to search for missing firefighters under a line of fire trucks caught in massive gas explosions in Kaohsiung, Taiwan, Friday, August 1, 2014. A series of underground explosions about midnight Thursday and early Friday ripped through Taiwan's second-largest city, killing scores of people, Taiwan's National Fire Agency said Friday. (Photo by Wally Santana/AP Photo)

An artist takes part in the festival “Statues en Marche” in Marche-en-Famenne, Belgium, July 20, 2019. Living statues are a common sight in many city centers, but it is rare to see such a diverse range of this peculiar form of street art for which performers must keep still for painfully long periods of time to create the desired illusion. (Photo by Yves Herman/Reuters)

Artists called “Le couple en chocolat” take part in the festival “Statues en Marche” in Marche-en-Famenne, Belgium, July 22, 2018. Living statues are a common sight in many city centres, but it is rare to see such a diverse range of this peculiar form of street art for which performers must keep still for painfully long periods of time to create the desired illusion. (Photo by Yves Herman/Reuters)

Women carry gas cylinders to fill them at a distribution point in Cairo January 19, 2015. Egypt is going through its worst energy crisis in decades and is seeking fresh sources of natural gas, which powers most of its homes and factories. (Photo by Mohamed Abd El Ghany/Reuters)

Guest gather in the street as the wait to attend the annual New York City Diner en Blanc, August 22, 2017 held this year at the plaza at Lincoln Center. The Diner en Blanc, the worlds only viral culinary event, a chic secret pop-up style picnic from France, the outdoor site – always a landmark location – is revealed at the last-minute. Guests are asked to dress entirely in elegant white, bring a picnic basket of food, fine china and silverware, white tablecloths, table and chairs. (Photo by Timothy A. Clary/AFP Photo)

Three workers demonstrating the different types of gas masks used in mine rescue work. (Photo by Fox Photos/Getty Images). December 1925