A woman looks for fruits to buy inside a bus called Sacolao in Santa Teresa neighborhood in Rio de Janeiro, Brazil, July 7, 2015. The bus, which began operating as a municipal initiative but has been taken over by a private enterprise, arrives every week in some neighborhoods to facilitate families with their grocery shopping and sells food at an affordable price, according to sellers. (Photo by Pilar Olivares/Reuters)

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)

Ecuadorian luthier Ivan Ibujes plays a guitar after repairing it at his shop in Quito, June 17, 2016. (Photo by Guillermo Granja/Reuters)

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