Scuba Diving – September 2019

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82 / SEPTEMBER/OCTOBER 2019 SCUBADIVING.COM

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xygen toxicity is one of the most sig-

nificant dangers nitrox divers face,

but fortunately it’s easily preventable.

Following training guidelines and plan-

ning dives conservatively can signifi-

cantly reduce your risk—but really un-

derstanding how oxygen toxicity affects

divers will give you all the incentive you

need to adhere to these guidelines.

WHAT IS IT?

Breathing oxygen at an increased par-

tial pressure for prolonged periods can

have harmful effects on the body; oxy-

gen becomes toxic if too many molecules

of it are present in our cells. There are

two main types of oxygen toxicity that

can affect divers: pulmonary toxicity and

central nervous system (CNS) toxicity.

Pulmonary oxygen toxicity is of less

concern to recreational divers as it oc-

curs with prolonged exposure to elevated

oxygen levels. This type of oxygen toxic-

ity can occur in divers doing very long

technical dives (in the range of six to 12

hours or more) and divers doing repeti-

tive technical dives over a period of days

or weeks.

It most commonly occurs in ICU pa-

tients and people undergoing hyperbar-

ic recompression treatment. In the ICU or

in a hyperbaric chamber, patients would

be breathing 100 percent oxygen for

time periods that far exceed typical dive

times, so there is only a small likelihood

that recreational nitrox divers would ex-

perience this type of oxygen toxicity.

If pulmonary oxygen toxicity occurs, it

ASK DAN

What is oxygen toxicity, and how can divers avoid it?

BY DIVERS ALERT NETWORK

generally begins with inflammation of the

upper airway then spreads to the lungs.

Left unchecked, the condition can re-

sult in alveolar damage, or collapse and

decline in/or loss of lung function. Dam-

age caused by this type of oxygen toxic-

ity is entirely reversible, and because this

type of oxygen toxicity occurs almost

exclusively in patients in clinical set-

tings, the consequences are not nearly

as grave as those associated with expe-

riencing CNS oxygen toxicity in the water.

Central nervous system oxygen toxic-

ity is the real concern for divers, includ-

ing both recreational nitrox divers and

technical divers. The condition can arise

without warning, and onset of CNS toxici-

ty can occur with very short exposures to

elevated partial pressures of oxygen. The

condition begins at the molecular level

and affects the complex of tissues that

make up the brain and spinal cord, caus-

ing tissue damage and seizures.

Understanding how molecular oxy-

gen disrupts the CNS requires an un-

derstanding of how the human nervous

system works. The nervous system com-

prises two opposing sides: the sympa-

thetic and parasympathetic nervous

systems. Every organ in the body is con-

trolled by one or often both of these