Scuba Forensics
By Dr Jolie Bookspan, Naui 7636

The science of crime is called forensics. Television forensic shows have become popular. Degree and certificate programs in various forensic specialities are the new trendy career. Real forensics is not like television forensics and often techniques shown on television are exaggerated, applied incorrectly, interpreted badly, or just false. Just as scuba diving in popular television shows is not always accurately portrayed, the forensics of scuba death is not much like television crime shows portray.

I am the science officer for the Vidocq Society (pronounced Vee-doc), an international forensic think-tank for solving cold case murders (www.vidocq.org). The Society allows 82 members by invitation only. The Vidocq, who is considered the founder of modern criminology. Vidocq was a former fugitive and police informant who became an expert in surveillance and disguise. Vidocq was the first to make plaster casts of foot and shoe impressions, and introduce record keeping and the study of ballistics into police work. As the science officer for the Vidocq Society, my job is to make sense of some of the physiology used ( and often not used) in forensic investigations. This article covers a few examples.

In a death that occurred during scuba diving, bubbles may be found in the body. How can you tell if they are from decompression sickness, from air embolism, or normal decomposition? The answer is that it is not straightforward to distinguish.

Bubbling from decompression sickness is dissolved gas coming out of solution from surfacing too rapidly or after staying at depth too long. Dives to about 20 feet (7m) or less usually do not result in a large amount of bubbling, but can in occasional cases. The process of staged decompression-making one or more stops in the water during ascent from depth-reduces, but does not necessarily eliminate, the evolution of bubbles from tissues. Bubbling continues in many locations in the body and usually begins immediately. Where there is significant missed decompression, bubbling begins during ascent.

Bubbling from an air embolism releases gas from the lungs following pulmonary trauma. Air in the lungs expands upon ascent as pressure decreases with decreasing depth. If the diver does not breathe out on the way up, pulmonary gas can escape directly into the pulmonary capillaries or veins then travel with blood flow into the left side of the hear to be pumped into arterial blood that travels around the body, until lodging in the brain, heart, lungs, or other areas. Expanding air on ascent can also overpressure the lung and make its own hole to get out and spread up under the skin (subcutaneous fascial planes) into the neck or downward into the abdomen. Gas may also be released into the pleural space resulting in a pneumothorax. Although this usually involves one lung, double (bilateral) pneumothoraces can occur. At the same time, with severe decompression sickness there may be so many bubbles that the lung can not filter them all, and there may be tearing of vessels and lymph allowing the bubbles to get into the arterial system. then the bubbles are arterial bubbles, as if from arterial gas embolism, although they are not from lung overpressure.

With decomposition, bacteria in the body produce gas after death. Although gas is usual in the portal/hepatic (liver) veins in as little as 12 hours after death, and within 36 hours in intra-vascular and soft tissue if the body is not refrigerated, there have been documented cases where the time was far shorter, more resembling the time frame for a diving accident, even where no diving accident had occurred. With post-mortem (after death) decomposition, in general an erect radiograph (upright X-ray) of the chest and abdomen show large amounts of gas in the right ventricle, aorta and neck veins. Head X-rays show gas in the cerebral (brain) vessels. Limb X-rays may show gas. You seldom see gas around the joints. The Òbusy areaÓ is the heart and great vessels. You need to be careful here. Gas from decompression accidents can be found with a similar distribution. Decomposition gas ends up everywhere, but an obvious place to see it is the heart and venae cava. With DCS you would expect gas more on the low pressure side of the system, though after death all intravascular pressure are equal at zero.

In a diving overpressure accident there can be gas in the cerebral arteries and the left and right ventricles of the heart. However, large amounts of gas may also be present in the right ventricle in off-gassing, decomposition, and from resuscitation. It is not clear-cut.

You can analyse the bubbles to see what kind of gas it is. If it is mostly nitrogen, then the possibility is higher that decompression sickness produced the bubbles. Hydrogen and methane in the recovered gas are a better indication of decomposition. However, if the examination was not done right, air can get into the body in many ways, including the syringe used to withdraw it. A gas-tight syringe needs to be used with care that no blood or air enter the syringe.

Also consider the case where a diver dies (or is killed) on the bottom from any non-diving cause. If the diver is recovered to the surface, gas will come out of solution and decompression bubbles can form in both intra-vascular and soft tissue even in the post-mortem state. A diver who dies while being treated for DCI in a decompression chamber will also have bubbling at post-mortem examination. This gas should theoretically be distinguishable from gas formed through embolism by the presence of gas in muscles and joints. Small amounts of gas in the liver are more often decomposition. Dead bodies brought up from depth may be full of intravascular gas, resulting in an erroneous conclusion of DCS or AGE, and bubbles/gas would be a combination of post-mortem off-gassing (given a sufficiently provocative dive profile) with a little contribution from post-mortem decomposition. In practice, it is difficult to distinguish.

A key point to remember is that death is rare from DCS in sport, commercial, military, and technical diving; perhaps a case per year at most. (The numbers of indigenous fishermen with devastating DCS and subsequent death from extreme scuba practices to support seafood restaurant chains is a separate and tragic issue to be covered in another article).

There are several common fallacies about determining time of death. One is that gastric emptying is a reliable indicator. In reality, it is highly variable. Two more events, stiffening of the body (rigor mortis) and livor mortis (purplish-red skin discoloration from blood settling) are greatly affected by common factors and provide only a general time window, not a specific hour or hours. Another widespread error is thinking that time of death is predictable from body temperature and cooling. the name for cooling of a body after death is algor mortis (Latin: algor is coolness; mortis means death). This cooling does not follow predictable time intervals as once thought. Many factors change the rate of body cooling post-mortem: ambient temperature and humidity, force of the wind, presence of rain or snow, clothing, the surface the body is resting on, if the body has been buried, even if just by leaves, submersion in water, and the water temperature. Fat people cool more slowly than thin ones. Large adults cool more slowly than small ones and children. The general principles that can be used to make educate guesses on land become nearly or completely useless for bodies recovered from underwater. There is no set number of degrees of cooling per hour.

How did the myth of predictability of post-mortem cooling begin? In 1710, English physician John Davey first used the then-new invention of the thermometer in a human body at autopsy. DaveyÕs experiments on the bodies of British soldiers were published based on h is work, which took place in the high heat of malta. Later pathologists following DaveyÕs published descriptions apparently did not place the thermometer inside the body, but in the armpit. Their publications of the inaccurate information of cooling became widely popularized and passed from school to school. It turns out that the widely held dogma that body temperature drops at a precise and steady rate of 1.6 degrees an hour (later rounded to 1.5 for ease of calculation) was never the case.

There is more to know about gas and bubbles, and the science of telling how and when a crime may have occurred. If you get ideas from television show, and avoid old fallacies, even if learned in school or from forensic books, and look further to learn the real science.

Sources - First Quarter 2007 copyright 1996 NAUI. All rights reserved.

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