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)

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

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)

A newly wed couple jumps to pose for their wedding photographs after their group wedding ceremony which was held as part of the Harbin International Ice and Snow Festival in the northern city of Harbin, Heilongjiang province January 6, 2015. The wedding ceremony was organised by the city government and 11 couples from China, Russia and Egypt participated in the ceremony. (Photo by Kim Kyung-Hoon/Reuters)

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

Crampus from Netherworld Haunted House with Amber Thompson, spa staff, at Bliss Spa at W Atlanta Downtown hotel on Thursday, October 7, 2014. A self-guided, dark attraction known for its over-the-top special effects, intense make-up, costuming and stunt actors as well as unique monsters, unusual themes and chilling detail, Netherworld Haunted House in Atlanta is taking over the Halloween holiday this season for its 18th season. (Photo by Hyosub Shin/AJC)

A fireman from the London Fire Brigade, wearing a smoke helmet. (Photo by Topical Press Agency/Getty Images). Circa 1908