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

Riot police arrest an anti-government protester in Ouagadougou, capital of Burkina Faso, October 30, 2014. Thousands of protesters marched on Burkina Faso's presidential palace after burning the parliament building and ransacking state television offices on Thursday, forcing President Blaise Compaore to scrap a plan to extend his 27-year rule. Emergency services said at least three protesters were shot dead and several others wounded by security forces when the crowd tried to storm the home of Compaore's brother. Security forces also fired live rounds and tear gas at protesters near the presidency in the Ouaga 2000 neighborhood. (Photo by Joe Penney/Reuters)

Riot police use a water cannon to disperse LGBT rights activist before a Gay Pride Parade in central Istanbul, Turkey, June 28, 2015. Turkish police fired water cannon and rubber pellets to disperse a crowd gathered in central Istanbul for the city's annual gay pride parade, a Reuters cameraman at the scene said. The police appeared intent on stopping the crowd gathering near Taksim Square, the cameraman said. Taksim is a traditional rallying ground for demonstrators and saw weeks of unrest in 2013. (Photo by Kemal Aslan/Reuters)

Riot police officers in position to crack down on demonstrators during a protest against Venezuelan President Nicolas Maduro, in Caracas on April 20, 2017. Venezuelan riot police fired tear gas Thursday at groups of protesters seeking to oust President Nicolas Maduro, who have vowed new mass marches after a day of deadly unrest. Police in western Caracas broke up scores of opposition protesters trying to join a larger march, though there was no immediate repeat of Wednesday's violent clashes, which left three people dead. (Photo by Juan Barreto/AFP Photo)

An unmanned Antares rocket is seen exploding seconds after lift off from a commercial launch pad in this still image from video shot by Matthew Travis of Zero-G News from the press area at Wallops Island, Virginia October 28, 2014. The 14-story rocket, built and launched by Orbital Sciences Corp, bolted off its seaside launch pad at the Wallops Flight Facility at 6:22 p.m. EDT/22:22 GMT. It burst into flames moments later, then plunged to the ground in a huge ball of fire and smoke, but authorities said no one was hurt. The cause of the accident was not immediately known. (Photo by Matthew Travis/Reuters/Zero-G News)

An approximately 8 year-old male orangutan named Siamang reacts under the influence of tranquilizer as it's being prepared to be released into the wild at a rehabilitation center in Kuta Mbelin, North Sumatra, Indonesia, Friday, July 10, 2015. The orangutans at the center were mostly rescued from palm oil plantations or confiscated from homes where they were kept as pet animals. Orangutan populations in Indonesia's Borneo and Sumatra island are facing severe threats from habitat loss, illegal logging, fires and poaching. Conservationists predicted that without immediate action, orangutans are likely to be the first great ape to become extinct in the wild. (Photo by Binsar Bakkara/AP Photo)

This picture taken on November 11, 2016 shows participants releasing a hot- air balloon during the Tazaungdaing Lighting Festival at Taunggyi in Myanmar' s northeastern Shan State. The skies of central Myanmar were set ablaze this week with the beginning of the Taunggyi fire balloon festival, one of the most beautiful and dangerous celebrations in Asia. Brightly coloured balloons with hundreds of homemade fireworks woven into their frames are sent soaring into the night sky, showering down cascades of sparks onto adoring crowds. (Photo by Ye Aung Thu/AFP Photo)

A protester gestures after he saw a dead protester in Kampala, Uganda February 15, 2016. At least one person has been killed in Uganda's capital Kampala as police clashed with opposition supporters after briefly detaining a top presidential candidate twice as he tried to hold campaign rallies days before a general election. Several people were wounded in the clashes as police fired bullets and tear gas while opposition supporters hurled rocks and erected street barricades in the capital's Wandegeya suburb, witnesses said according to a Reuters news agency report. (Photo by Goran Tomasevic/Reuters)