According to Mack S. House Jr., a forensic research diver and author of Underwater Forensics Research: Commercial Scientific Diving, investigators are trained with equipment that land-based investigators may never see. They might utilize a mask with lighting on it, for example, or have a video recorder with a remote monitor that allows people on the boat to see what they see. These divers must also know courtroom procedure, evidence documentation, and proper evidence handling. But first, and foremost, they must understand the effects of being under water so they avoid getting themselves into dangerous positions.
Of the two primary concerns for divers, the first is hyperbaric exposure. "Boyle's Law," says House, "states that the volume and pressure of an ideal gas is constant given a constant temperature. It defines the relationship between the volume of the air space and the ambient pressure." Air-containing cavities, such as the sinuses and lungs, react to sudden pressure changes, and divers must pay attention to the effects of decompression. Breathing compressed air underwater can increase gas pressure in the lungs. In addition, Boyle's Law affects the diaphragm. "The greater the ambient pressure," says House, "the more the diaphragm is depressed against the delivery aspect of the regulator, thus requiring less negative inspiritory force."
Second, divers may also sustain "barotrauma," or physical damage to body tissues as a result of difference in pressure between an air space inside or beside the body and the surrounding gas or liquid. Damage occurs in the tissues around the body's air spaces, especially the lungs.
In addition, divers must be informed about long-term psychological effects from finding and handling human decomposition, specifically trauma and burn-out. If they fail to understand what can happen, they can become withdrawn and lose their edge as investigators.
The medical examiner who will decide such things as time, cause, and manner of death must know as much as possible about underwater conditions, because various factors affect the body during decomposition. For example, "refloat" is the time it takes a body to float to the surface after having initially sunk, while scavenger activity can destroy evidence for cause of death. Sometimes bodies in water generate adipocere, or a soap-like substance than can be a preservative, but prolonged immersion makes the skin macerate and become vulnerable to peeling.
"Studies have shown," House states, "that a body will cool faster submerged in water than it will exposed to air." This is due to radiation, or the transfer of energy by non-particulate means, and to convection, the transfer of heat from the victim to the surrounding water. Depending on the weather and water environment, more often than not the submerged victim will succumb to putrefaction at a greater rate than does an open-air victim.
Remains in poor condition present special problems for handling, and thus need extensive documentation. The diver must make a thorough search of the area for additional evidence, e.g., jewelry and clothing, prior to moving any body part. The remains are placed inside a body bag while underwater to prevent loss of evidence as it is taken to the surface. In addition, the diver must take precautions against contamination.
To become certified as an underwater forensic research diver some investigators take a Public Safety Diver course, but like other professional trainers House believes there should be a formal program that focuses on many additional subjects. Among them, he would include anatomy and physiology, psychology, human nutrition, the use of commercial diving equipment, and Coast Guard regulations. The more training such divers acquire the better work they can do, especially in difficult cases.