Snorkel (swimming)

Snorkel

Snorkel, worn with diving half mask
Uses	Breathing while face down at the surface of the water
Related items	Diving mask, Swimming goggles

A snorkel is a device used for breathing atmospheric air when the wearer's head is face downwards in the water with the mouth and the nose submerged. It may be either a separate unit, or integrated into a swimming or diving mask. The integrated version is only suitable for surface snorkeling, while the separate device may also be used for underwater activities such as spearfishing, freediving, finswimming, underwater hockey, underwater rugby and for surface breathing while wearing scuba equipment. A standard snorkel is a curved tube with a shape usually resembling the letter "L" or "J", fitted with a mouthpiece at the lower end and made from plastic, synthetic elastomers, rubber, or light metal.^[1] The snorkel may have a loop or a clip to attach it to the head strap of the diving mask or swimming goggles, or may be tucked between the mask-strap and the head.^[2] Some snorkels are fitted with a float valve at the top to prevent flooding if the top opening is immersed, and some are fitted with a water trap and purge valve, intended for draining water from the tube.

The current European Standard specifies limits for length, bore and internal volume for separate snorkels. Some types of integrated mask-snorkel combinations and anti-flooding valves are banned from manufacture and sale in some countries as unsafe.^[3]

Snorkels constitute respiratory dead space. When the user takes in a fresh breath, some of the previously exhaled air which remains in the snorkel is inhaled again, reducing the amount of fresh air in the inhaled volume, and increasing the risk of a buildup of carbon dioxide in the blood, which can result in hypercapnia. The greater the volume of the tube, and the smaller the tidal volume of breathing, the more this problem is exacerbated. Including the internal volume of the mask in the breathing circuit greatly increases the dead space.^[4] Occasional exhalation through the nose while snorkeling with a separate snorkel will slightly reduce the buildup of carbon dioxide, and may help in keeping the mask clear of water, but in cold water it will increase fogging of the viewport. To some extent the effect of dead space can be counteracted by breathing more deeply and slowly, as this reduces the dead space ratio and work of breathing.