Your dive com­puter re­ally doesn’t know any­thing about you

Scuba Diving - - TRAIN - ERIC DOU­GLAS has been a dive in­struc­tor, medic, and author on scuba safety and ad­ven­ture. Visit his web­site at books­by­eric.com. BY ERIC DOU­GLAS

Ev­ery year dur­ing the Florida- lob­ster mini sea­son, Greg got bug fever. He had al­ready in­vited friends and fam­ily over for a cook­out the next day, so he needed to catch his limit — he wanted to wow them with his lob­ster grilling. He wasn’t hav­ing much luck fi nd­ing good lo­ca­tions with le­gal- size lob­ster, though. That meant he had to keep div­ing. He wasn’t go­ing to let everyone down.


Greg was 37 years old and dived nearly ev­ery week­end. He was in good shape and didn’t take any med­i­ca­tions. He was ex­pe­ri­enced, with more than 10 years since his cer­ti­fi­ca­tion.


Over a 14-hour pe­riod, Greg made six dives from a pri­vate boat with a cou­ple of bud­dies. He claimed to be us­ing a 32 per­cent ni­trox mix on all of them and used a dive com­puter to track his sta­tus.

His dive se­ries in­cluded: 1) 85 feet of sea­wa­ter (fsw) for 50 min­utes; 2) 75 fsw for 50 min­utes; 3) 75 fsw for 35 min­utes; 4) 70 fsw for 50 min­utes; 5) 85 fsw for 50 min­utes; and 6) 70 fsw for 50 min­utes. Over­all, the divers recorded four hours and 45 min­utes of bot­tom time through­out the day, but did not record their sur­face in­ter­vals. In­stead, they fol­lowed their com­puter's rec­om­men­da­tions. From the be­gin­ning of the first dive to the end of the last, they spent ap­prox­i­mately nine hours and 15 min­utes out of the

wa­ter. Greg was fi­nally done for the day and as­cended to the sur­face for the last time at 10 p.m.


About a half an hour af­ter Greg and his bud­dies made it back to the dock, he no­ticed a pain in his up­per left arm. The pain was in both his bi­ceps and tri­ceps; he de­scribed it as three out of 10, with 10 be­ing the worst pain imag­in­able. He thought it was prob­a­bly just mus­cle strain from car­ry­ing tanks and his dive equip­ment.

The pain per­sisted for an­other half an hour, and Greg re­al­ized there might be a big­ger prob­lem. He be­gan breath­ing 100 per­cent oxy­gen us­ing a de­mand valve, and a friend drove him to a lo­cal hospi­tal. The hospi­tal hap­pened to have a hy­per­baric cham­ber.

The treat­ing physi­cian con­ducted a neu­ro­log­i­cal as­sess­ment and didn’t find any prob­lems, but the pain con­tin­ued. Greg told the doc­tor that the pain was dif­fer­ent than any­thing he had ever felt be­fore. There was no way he could move or hold his arm that made it feel any bet­ter, or worse.

The doc­tor gave Greg a U.S. Navy Treat­ment Ta­ble 6. Two and a half hours af­ter Greg first no­ticed the symp­toms, he en­tered the hy­per­baric cham­ber. When the nearly five-hour treat­ment ended, Greg’s pain was al­most gone. He did have a slight burn­ing feel­ing in his chest that was new, but that was at­trib­uted to the ex­po­sure to high con­cen­tra­tions of oxy­gen. It relieved it­self later that day.

Greg’s doc­tor told him to wait six weeks be­fore re­turn­ing to div­ing. The resid­ual arm pain less­ened over a few days, and a week later, Greg re­al­ized it was gone. He has since re­turned to div­ing, although now he doesn’t do as many dives in a sin­gle day as he did the day he was hurt.


Greg made an ag­gres­sive se­ries of dives, but he stayed within the lim­its of his dive com­puter. He should have been fine, right?

Wrong. Dive com­put­ers are won­der­ful tools that have rev­o­lu­tion­ized the way we dive, giv­ing us more bot­tom time and mak­ing it eas­ier to plan mul­ti­ple dives in a sin­gle day. How­ever, they are sim­ply math­e­mat­i­cal al­go­rithms, just like dive ta­bles. The ad­van­tage they give is they re­cal­cu­late your depth and time on a reg­u­lar ba­sis, es­sen­tially giv­ing you a cus­tom dive ta­ble ev­ery minute or so. The down­side to this is they cut off the built-in safety mar­gin that square dive pro­files on a dive ta­ble pro­vided.

Most dive com­put­ers also do not an­a­lyze your heart rate, hy­dra­tion level, fit­ness level, ac­cu­mu­lated blood gases in your body, or any of the other fac­tors that could con­trib­ute to de­com­pres­sion ill­ness. Fol­low­ing them blindly, or div­ing ag­gres­sively us­ing a com­puter, still leaves the pos­si­bil­ity of a div­ing-re­lated in­jury.

As a side note, af­ter his treat­ment, Greg ad­mit­ted he wasn’t sure what his breath­ing-gas mix had been on the day of his in­jury. He dived as if he were on a 32 per­cent ni­trox mix, but he wasn’t an­a­lyz­ing each tank be­fore each dive, so he wasn’t sure how much ni­tro­gen he was in fact in­hal­ing. That is a se­ri­ous mis­take. Ni­trox can give divers ad­di­tional bot­tom time on ev­ery dive be­cause they are ab­sorb­ing less ni­tro­gen with each breath. Greg put him­self at risk by not an­a­lyz­ing the tanks. If they were filled with air, or a lower oxy­gen mix­ture, he was div­ing be­yond the lim­its of his breath­ing gas. If they hap­pened to be filled with a higher con­cen­tra­tion of oxy­gen, he risked the pos­si­bil­ity of an oxy­gen seizure.

Greg likely had a case of what is called De­com­pres­sion Ill­ness (DCI) Type 1 or Pain-only DCI. DCI is a blan­ket term that in­cludes Type 1, Type 2 Neu­ro­log­i­cal DCI, and Ar­te­rial Gas Em­bolism. Pain-only DCI ex­hibits as pain in the body, typ­i­cally in the ex­trem­i­ties and gen­er­ally in joints like shoul­ders and el­bows, that you can’t oth­er­wise ex­plain. It doesn’t change no mat­ter how you move the ex­trem­ity. The doc­tor’s neu­ro­log­i­cal as­sess­ment in­di­cated there was no prob­lem, so ni­tro­gen-gas bub­bles had not formed against a nerve, which would have caused numb­ness or tin­gling. In the worst cases, neu­ro­log­i­cal symp­toms can cause paral­y­sis or death.

It isn’t a defini­tive cause of de­com­pres­sion ill­ness, but most ex­perts agree that de­hy­dra­tion is likely a con­tribut­ing fac­tor. Greg spent 14 hours on the wa­ter on a boat div­ing. He made six dives and rested be­tween each one. Div­ing it­self causes a diver to be­come de­hy­drated through im­mer­sion di­ure­sis. In short, wa­ter pres­sure forces blood in your ex­trem­i­ties into your body core. Your kid­neys rec­og­nize that you have too much fluid in your body and choose to elim­i­nate it. This is why you al­ways have to uri­nate when you dive. With that much time on a boat while div­ing, it would take a con­scious ef­fort for Greg to drink enough flu­ids to not be de­hy­drated.

On the up­side, Greg did one thing ex­actly as he should have. He re­al­ized he had a pain in his arm that didn’t make sense and didn’t feel like any­thing he had ever felt be­fore. It didn’t change no mat­ter how he moved his arm. Within a half an hour of not­ing the pain, he was breath­ing 100 per­cent oxy­gen and head­ing to the hospi­tal. Within two and a half hours, he was en­ter­ing a hy­per­baric cham­ber for treat­ment.

Statis­tics from Divers Alert Network say that the av­er­age wait time be­tween symp­tom on­set and treat­ment is closer to 17 hours. Most divers in this same sit­u­a­tion would have cho­sen to wait un­til the morn­ing to see if the pain was still there be­fore seek­ing help. Greg’s de­ci­sion to seek help im­me­di­ately likely helped with the rapid res­o­lu­tion of the prob­lem. While still treat­able the next morn­ing, more in­sult to the body tis­sues would have hap­pened, and the in­jury would have been harder to treat.

“Dive com­put­ers also do not an­a­lyze your heart rate, hy­dra­tion level, fit­ness level, ac­cu­mu­lated blood gases in your body, or any of the other fac­tors that could con­trib­ute to de­com­pres­sion ill­ness.”

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