Course Outline

Diving has its own terminology and language. Below are some examples you should know.

  • SCUBA or scuba is short for self-contained underwater breathing apparatus. Typically, scuba equipment consists of a cylinder containing compressed breathing-grade gas with virtually all the moisture extracted. For this reason, it is recommended you hydrate well before diving.
  • Open circuit (OC) is the most common form of scuba equipment. Using OC, you inhale breathing gas from your cylinder via a scuba regulator and exhale gas into the water.
  • Rebreather reuses all the exhaled gas, which filters through a scrubber. The scrubber removes the carbon dioxide and adds just enough oxygen to compensate for the portion of the inhaled gas that was metabolized by the diver’s body. This recycled and cleaned gas is then rebreathed by the diver. Some of the advantages of using a rebreather include longer bottom times, fewer bubbles, quieter operation, better interaction with marine life, and the potential to dive deeper for longer. There are many types of rebreathers on the market, and each one requires specific training.
  • Nitrox is air with an increased percentage of oxygen, typically 32% or 36%. (Normal breathing air consists of approximately 78% nitrogen, 21% oxygen, plus various other trace gases.) The decreased percentage of inert nitrogen in nitrox may help reduce the risk of decompression sickness (DCS). Other benefits of using nitrox may be that it allows for more dive time and less surface interval time and may improve your respiratory rate. There are, however, specific risks when using nitrox, and additional training is required to use this gas.
  • No decompression limit (NDL) is the maximum allowable dive time a diver can remain at a specific depth and ascend directly to the surface without requiring decompression stops. (Note: Decompression diving has specific risks and requires specialized equipment and special gases. Further training is required.) Basic decompression theory will be discussed later in the course, including the use of PDCs to monitor your NDL.
  • Safety stop is a recommended stop for 3 to 5 minutes at 5 meters/15 feet. It is recommended that divers make a safety stop to finish every dive. Note: This is not a decompression stop; it is an additional safety recommendation before actual decompression is required. Most modern PDCs will build in a safety stop. In an emergency, divers can skip this safety stop.
  • Buddy is a certified dive friend. When you become a certified Open Water 20 diver, you should always dive with a buddy so that you can watch out for each other and share the experience. Always stay within close contact with your buddy (3 meters/10 feet in average conditions). The buddy system is a safer way to dive because each diver has a buddy to assist him or her if needed. Diving with a buddy also means you also have two minds to solve underwater problems and two sets of hands and eyes to complete underwater tasks. Decide before the dive who will be the main dive leader and then swim alongside each other to stay together.
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