Consideration needs to be given to traditionally dangerous items and material such as explosives, toxic chemicals, dangerous equipment, etc. If you are an evidence technician, and not a bomb squad member, don't attempt to collect and render safe a WWII grenade found at the scene of a skinhead hate crime. Call the bomb squad. Other evidence is less dramatic in its potential danger to you, but still equally deadly.
Great caution is indicated.
Take your time, and be thoughtful in your method of evidence recovery. You may not notice a junkie's syringe in the tall pile carpet of the bedroom you are processing, and if you have not brought in proper lighting and carefully searched the room in a sequential manner, you may not know the syringe is there until you step into it, it punctures your shoe and the needle sticks into your toe. They include bacterial meningitis, tuberculosis, and Hepatitis B. Contact with the saliva, nasal contents, or product of coughing of a subject may expose you to these potentially fatal diseases. And these are only some of the diseases to be concerned about. There are procedures to protect forensic professionals from disease transmission, but they must be followed religiously without deviation.