surface supplied vs back gas

Surface Supplied vs. Back Gas

by Dr. Thomas Powell:

The public safety diving world is one that has been made up of a “hodge-podge” of equipment for years. The reason for this mixture of equipment is largely based upon a lack of two items. These two items are funding and knowledge. In many cases, public safety dive teams are developed because a group of volunteers see a community-based need and begin to organize without an understanding of standardized public safety dive operations. Relying on basic open water credentials, these divers piece together usable equipment that can allow personnel to “make-due” until funding becomes available. The problem is that these divers show they can make something work and future funding comes rarely and in small amounts. Emergency Response Diving International (ERDI) has worked for many years to try and encourage dive teams to standardize the equipment used among team members and within territories. If divers know where to find tools, snaps, quick releases, and other items on one set of gear, the standardization of equipment ensures they can always find those items and possibly provide assistance, to any other teammate.

Air delivery is one topic that must be discussed and planned on any dive team. Typically, when developing a dive team, leadership personnel choose one air delivery method and stick with it in perpetuity. The choice comes down to standard back gas, or surface supplied gas. Any trained diver in the modern world should have a general understanding of back gas and how a diver uses this type of air delivery system. Essentially, a cylinder of some type is mounted to the diver’s back and the diver breathes gas through the use of a standard regulator system. In contrast, with surface supplied gas the diver is connected to the surface using an umbilical. Breathing gas is pumped to the diver through this umbilical throughout a dive.

Back Gas

The use of back gas has both positives and negatives. The first line item that must be reviewed is cost. A new dive team often has an easy time locating and procuring cylinders at a reasonable cost. These cylinders are often simple to maintain and can remain available for quick and easy use. After all, almost every diver trained today already knows the basics on how to use a single cylinder for diving purposes. The problem with using back gas is that your gas will only last so long. Public safety divers are often performing arduous or stressful activities while being subjected to multiple problematic factors. A stressed diver often breathes gas faster. For this reason, dive times may be shortened and the team may be faced with swapping cylinders with high frequency. The team must also plan for refilling these used cylinders. If you are a sport diver, do not look at public safety diving as you would a fun reef dive in the Caribbean. Instead, understand that public safety divers follow the “rule of thirds.” These divers will use one-third of their gas to swim to a target area and perform a search.  A second third is used to return to the entry point and to remain available during an emergency. The final third must be maintained for possible decontamination needs. These factors all create limiting potential for back gas public safety dives.

Lastly, back gas is monitored by the diver. This can become an issue when dive operations are performed in black-water environments or when divers become too focused on operational tasks. To overcome this problem, tenders must be trained to use communications systems or methods of various types to help the diver remain focused or on task. This may also create a limiting factor for dive times based upon the individual air consumption rates of divers that must be monitored by shore personnel as secondary oversight for gas reserves.

Surface Supplied Gas

Surface supplied gas presents its own set of positives and negatives. First, the team using a system such as this must have the proper surface gas supply system, umbilicals, and masks or helmets with proper inputs. This type of system requires both divers and surface personnel to be trained to manage and operate the system while monitoring diver safety at all times. The reality is that there is a similar level of training required when compared to using back gas, but the entire team must be trained to work together and depend on one-another with a reduced level of diver-based responsibility (in regard to self-monitoring).

The reality of surface supplied gas systems is that divers may essentially have an unlimited quantity of gas available. When compared to using back gas, this lends to an elimination of swapping out cylinders and a larger comfort zone in regard to completing tasks without worry associated with gas availability. The related problem is that divers may choose or be asked to stay underwater for longer periods when safe practice suggests public safety divers adhere to restricted dive times.

Both surface supplied gas and back gas systems can work in regard to public safety dive applications. A team must weigh the pros and cons of each type of air delivery system based on need, use, and operational activity. Most teams will choose to purchase one type of system and then use that system type moving forward. With surface supplied gas, a diver maintains an almost unlimited gas supply but the team must work at all times as a well-oiled machine. The diver cannot break free from his or her tether and operate without surface support. Back gas allows the diver to operate in an independent fashion if needed, but also allows for a situation where surface personnel must be trained to provide secondary monitoring for the diver, as well as operational oversight. Both types of systems are functional and support dive operations, but each must be considered for best value and usability.

– Thomas Powell – Owner/Instructor Trainer – Air Hogs Scuba, Garner, NC

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