The PADI Enriched Air Diver is excellent dry course (theory based) that will allow you extend your bottom time by increasing your no decompression limits and ultimately dive safer. 

When mixing a higher percentage of oxygen in your cylinder rather than the standard air (21 percent) to anywhere from 23% to 40% you could potentially extend your bottom time at certain depth. 

During diving, water pressure causes the nitrogen we breathe to be absorbed into the bloodstream. The higher the pressure, the more nitrogen is absorbed, and the greater the risk of decompression illness. The higher the oxygen percentage in your air tanks, the less nitrogen we absorb, leading to a longer no-decompression limit and a longer dive time.

If you are like us and want to be safer when diving and spend more bottom with the added advantage of almost zero fatigue the next day then jump on a Nitrox course