## What Does BAR Stand for in Scuba Diving?
BAR is an acronym that stands for Breathed Air Ratio. It is a measure of the percentage of oxygen in a scuba diving gas mixture. The BAR is expressed as a percentage, with 100% BAR representing pure oxygen.
The BAR is important because it affects the diver’s decompression requirements. The higher the BAR, the more oxygen the diver is breathing, and the shorter the decompression time required. Conversely, the lower the BAR, the less oxygen the diver is breathing, and the longer the decompression time required.
### BAR and Decompression
The decompression tables used by scuba divers are based on the assumption that the diver is breathing air with a BAR of 100%. If the diver is breathing a gas mixture with a lower BAR, then the decompression time must be adjusted accordingly.
The following table shows the decompression times for different BARs:
| BAR | Decompression Time |
|—|—|
| 100% | 1 hour |
| 80% | 1 hour 30 minutes |
| 60% | 2 hours |
| 40% | 2 hours 30 minutes |
| 20% | 3 hours |
As you can see, the decompression time increases significantly as the BAR decreases. This is because the diver is breathing less oxygen, which means that their body must take longer to eliminate the nitrogen that has been absorbed into their tissues.
### BAR and Altitude
The BAR is also affected by altitude. The higher the altitude, the lower the atmospheric pressure. This means that there is less oxygen available in the air, which results in a lower BAR.
The following table shows the BAR at different altitudes:
| Altitude (feet) | BAR |
|—|—|
| 0 | 100% |
| 1,000 | 94% |
| 2,000 | 89% |
| 3,000 | 84% |
| 4,000 | 80% |
| 5,000 | 76% |
As you can see, the BAR decreases significantly as the altitude increases. This means that divers who are diving at high altitudes must be aware of the potential for decompression sickness and adjust their decompression times accordingly.
### BAR and Nitrox
Nitrox is a scuba diving gas mixture that contains a higher percentage of oxygen than air. The BAR of nitrox is typically between 32% and 40%.
Nitrox can be used to reduce the diver’s decompression requirements. However, it is important to note that nitrox can also increase the risk of oxygen toxicity. Therefore, it is important to use nitrox only under the supervision of a qualified dive professional.
### Conclusion
The BAR is an important concept for scuba divers to understand. It affects the diver’s decompression requirements, as well as their risk of decompression sickness and oxygen toxicity. By understanding the BAR, divers can make informed decisions about the gas mixtures they use and the dives they make.