A year ago, Typhoon Haiyan created a series of storm surges that left several thousand people dead and around four million homeless. Lasse Petersen was one of thousands of aid workers who flew to the Philippines in the immediate aftermath of the typhoon.
"When we arrived, we decided to focus our efforts on repairing schools," Petersen says.
"In the poor neighbourhoods where we were working, schools were usually the most solidly constructed buildings. In the early stages, they were used as emergency accommodation for refugees, then as storage facilities for aid consignments and as soup kitchens. Finally they were used as classrooms again as refugees either repaired their own houses or were provided with temporary accommodation.
"Twelve months on, there is a lot still to do. Essential services, such as hospitals, power and water, have been restored, but many public buildings are still waiting to be repaired."
Petersen's first deployment was to Papua New Guinea in 2004, helping people whose village was destroyed by a volcanic eruption. Since then, he has worked in dozens of disaster zones, from earthquakes and floods to hurricanes and tsunamis. He tells me about his experiences after the Japanese tsunami - one of the first disasters to be televised live.