As official investigations continue into the huge fertiliser facility blast in West, Texas, that killed 14 and injured at least 200 on 17 April, questions are being asked as to what was stored on the site, how the explosion happened and whether adequate safety precautions were in place.
"Investigators from the US Chemical Safety Board arrived on the scene last Thursday evening," Jean Gonsoulin, a spokeswoman for the board, told New Scientist.
Like 6000 other plants around the US, the facility stored, blended and distributed fertiliser - mainly anhydrous ammonia - to local farmers. Whether the plant also stored ammonium nitrate, a fertiliser doubling up as an explosive used in quarrying rock, is still unclear.