An investigation of San Francisco's 911 dispatch system found that 27 percent of first responders arrive late on the scene of high-priority medical emergencies. Many of the delays are the result of slow processing of 911 calls. The review of about 200,000 emergency medical calls during a four year period found that at least 439 people died while waiting for a late ambulance or after delayed medical help arrived. San Francisco officials are exploring potential solutions to reduce ambulance delays.