Why is it recommended that a snorkel not exceed 18 inches in length?

A snorkel length of 18 inches or less is recommended primarily to ensure effective functioning during use. If the snorkel is too long, there can be issues with dead space, which refers to the volume of gas in the snorkel that is not utilized for breathing. This can lead to a buildup of carbon dioxide (CO2) because when a diver exhales, some of that exhaled air remains trapped in the snorkel rather than being expelled effectively. Consequently, if a snorkel exceeds 18 inches, it may not allow for adequate clearing of CO2, which can result in discomfort or a feeling of breathlessness. Keeping the snorkel shorter helps maintain a more efficient flow of air, making it easier for the diver to breathe and manage their airflow.

In contrast, while discomfort, swallowing risk, and carrying difficulty are considerations, they are not the primary reasons for the 18-inch guideline, focusing specifically on airflow and safety during use is paramount in underwater breathing activities.