Answer:
because they need to check if the burnt substrate had a gasoline or other flammable material.
Explanation:
Scientists need to compile substrate samples in the case of arson, because by analyzing the burnt substrate and analyzing the deepest substrate (which may not be burned), scientists can see if the fire started naturally or if it had human influence . This is because, if in the burned substrate they find substances of flammable material, such as gasoline, they will be able to prove that the fire was initiated by the action of human beings on purpose.
Because fire heats the air, making it much thicker and uses up oxygen. if it runs out of oxygen, it cant keep itself lit.
