Nevertheless, it has drawbacks that can keep it from detecting just blood that has been shed in a crime. First, it also flouresces in the presence of copper or an alloy of copper. Second, it will also detect the small amounts of blood present in urine and it can be distorted if animal blood was present in the room that is being tested. The final drawback is that it is extremely carcinogenic and must be used by technicians clothed in hazardous material (hazmat) suits.