▁lead ▁to ▁sc uba ▁acc idents . ▁It ▁is ▁less ▁of ▁a ▁problem ▁with ▁surface ▁supplied ▁div ing ▁as ▁the ▁depth ▁that ▁the ▁diver ▁can ▁sink ▁to ▁is ▁limited ▁by ▁the ▁um bil ical ▁length , ▁and ▁a ▁sudden ▁or ▁rapid ▁descent ▁can ▁often ▁be ▁quickly ▁stopped ▁by ▁the ▁tender . ▁In ▁early ▁div ing ▁using ▁co pper ▁hel m ets ▁and ▁a ▁limited ▁flow ▁air ▁supply , ▁a ▁sudden ▁rapid ▁descent ▁could ▁lead ▁to ▁severe ▁hel met ▁s que e ze , ▁but ▁this ▁is ▁prevent ed ▁by ▁demand ▁supplied ▁gas , ▁and ▁neck ▁d ams ▁on ▁later ▁hel m ets , ▁which ▁allow ▁water ▁to ▁flo od ▁the ▁hel met ▁until ▁the ▁gas ▁supply ▁catch es ▁up ▁with ▁the ▁compression . ▁Sur face ▁supply ▁ens ures ▁that ▁the ▁gas ▁supply ▁will ▁not ▁run ▁out ▁suddenly ▁due ▁to ▁an ▁unexpected ▁high ▁demand , ▁which ▁can ▁de ple te ▁sc uba ▁supply ▁to ▁the ▁extent ▁that ▁there ▁may ▁not ▁be ▁enough ▁left ▁to ▁surface ▁according ▁to ▁plan . ▁Any ▁sudden ▁increase ▁in ▁depth ▁can ▁also ▁cause ▁bar ot ra uma ▁of ▁the ▁ears ▁and ▁sin uses ▁if ▁the ▁diver ▁cannot ▁equal ise ▁fast ▁enough . ▁ ▁Acc ident ▁statistics ▁There ▁is ▁very ▁little ▁reliable ▁data ▁describing ▁the ▁dem ograph ics , ▁activities ▁and ▁acc idents ▁of ▁the ▁technical ▁div ing ▁population , ▁and ▁conclus ions ▁about ▁accident ▁rates ▁must ▁be ▁considered ▁tent ative . ▁The ▁ 2 0 0 3 ▁D AN ▁report ▁on ▁decom pression ▁ill ness ▁and ▁d ive ▁fatal ities