Neutral Buoyancy for Public Safety Divers -

5 Reasons Why Neutral Buoyancy and Trim Are Important for Public Safety Divers

Article by Aaron Bradshaw, Air Hogs Scuba

As public safety divers, we often enter the water over-weighted due to the amount of gear we carry, and it is standard operating procedure for many teams to crawl along the bottom during a search. There are times when this is required—due to conditions or the need to remain on the bottom to work—but it shouldn’t always be the default.

Neutral buoyancy is a state of equilibrium in which a diver is neither rising nor falling in the water column. This balance is achieved by managing the three “air bladders” available to public safety divers: the wing/BCD, dry suit, and lung volume. The wing (or BCD) serves as the primary buoyancy control device, while the dry suit contains just enough gas to offset suit squeeze and maintain thermal protection. Lungs act as fine controls. The more over-weighted a diver is, the more air must be added and managed in the wing.

Trim is the next element once you achieve neutral buoyancy. Proper trim typically means a horizontal body position in the water (depending on the bottom terrain), with fins angled up so they don’t drag and disturb the environment.

I recall a specific training site used by our team and other local groups—a pond near a local station. Its plant growth is dense, and fine silt rests on top of that growth. We’ve run searches there for everything from small objects like shell casings to larger items like rifles and human-sized dummies. Some lessons learned at this site—and others—stand out.

Certainly, there are times when divers must carry extra weight or may even dive without fins, crawling along the bottom. Consider the techniques in this post as an additional tool in your toolkit. These buoyancy and trim skills are required for many advanced ERDI courses, such as Confined Space Operations.

Crime Scene and Evidence Preservation

The last thing we want to do as public safety divers is destroy or disturb a crime scene or evidence. ERDI courses—starting with ERD 1—delve deeply into proper evidence collection and documentation, and this focus continues through ERDI Crime Scene Investigation courses. Without proper buoyancy and trim, evidence may be disturbed or destroyed.

The pond mentioned above is like others in our area where we regularly search for evidence. It may take multiple careful searches to find smaller items such as shell casings. A diver “roto-tilling” or crawling the bottom can easily move, degrade, or destroy that evidence.

Visibility

Most public safety divers aren’t lucky enough to conduct their recovery dives in crystal-clear water. In my area, visibility is often limited—though we usually start with some visibility. Achieving neutral buoyancy may allow divers to search without disturbing that delicate silt layer more than necessary. Finite, hands-on searching typically causes far less disturbance than a fully laden diver who kicks up silt and drags gear along the bottom.

In such challenging environments, the odds are stacked against us, so we should capitalize on any visibility we have. A few years ago, an instructor placed items in our training pond for a group of ERD I and ERD II students. The pond had 2–3 feet (about 1 meter) of plant growth, and silt covering the leaves would drop visibility to zero if disturbed. Diver after diver searched but couldn’t find the last few items. The reason? With poor buoyancy, they were fighting the plant growth and reducing visibility.

After a debrief, we reset with proper buoyancy and trim. By staying above the plant growth and probing vertically—rather than kicking through silt—we found every item in about 30 minutes. With these new skills, subsequent searches were much more efficient, and many items were located visually, thanks to the improved water clarity.

Fatigue

Over-weighting a diver more than necessary goes beyond disturbing evidence or visibility: it also increases fatigue, accelerates gas consumption, and reduces the effectiveness of a search. Public safety divers are already burdened with heavy gear and mission tasks. Properly weighting the diver removes unnecessary stress.

When a diver has neutral buoyancy and good trim, each kick results in more efficient movement and better control in the water. A less fatigued diver can complete more dives with a higher success rate—and is also more effective in tender or support roles once out of the water.

Safety

As a team leader and public safety diver, safety is always on my mind—and it should be on yours as well. Proper weighting and neutral buoyancy help avoid a “see-saw” dive profile, ensure safer ascent rates, and reduce fatigue. Fatigue, in turn, leads to poor decisions and compromises safety. Our primary mission is always to bring our teams home safely.

Good buoyancy and trim also let you remain above or navigate around potential hazards like sharp debris, entanglement risks, steel cables, or boat rigging.

Search Efficiency

A properly trimmed, neutrally buoyant public safety diver who uses non-silting kicks will be far more efficient in many search scenarios. Fatigue impairs search efficiency, and when visibility drops, efficiency suffers further.

Each time an area must be searched a second or third time, the odds of disturbing evidence increase. Plant life can hold silt that, once kicked up, covers the object of interest. Crawling or “roto-tilling” the bottom may shift or destroy evidence entirely.

Moving Forward

If you want to improve these skills, consider holding a dedicated buoyancy and trim workshop. Perform weight checks, verify your weighting in the water, work on fin techniques, and practice trim as a team. In addition to ERDI courses, both SDI and TDI offer excellent programs to broaden your team’s knowledge. Many of our divers have taken TDI courses—such as Intro to Tech, Cavern, and Cave—to further hone these buoyancy and trim skills.

About the Author
Aaron Bradshaw is a Public Safety Diver and Instructor with Air Hogs Scuba. He has extensive experience in ERDI courses and is passionate about improving safety, efficiency, and outcomes for public safety dive teams.