LONDON—Authorities said 29 people were taken to the hospital with breathing difficulties on Wednesday after a “high quantity of chlorine gas” leaked in a swimming pool at the London sports complex that hosted the 2012 Summer Olympics. The London Fire Brigade said around 200 people were evacuated after the chlorine gas was discharged inside the Aquatics Center at the Queen Elizabeth Olympic Park in east London due to a “chemical reaction.” The brigade said it took 29 people to the hospital and assessed another 48 people at the scene. Most of those affected reported minor breathing difficulties, it said. The fire service declared a “major incident” and sent a large team of emergency workers including 13 ambulance crews and members of its hazardous area response team. Surrounding roads were cordoned off and members of the public were denied access to the park. Local residents were asked to close their doors …