Shipwrecks are among the most fascinating dive sites to explore; they allow us to get up close and personal with marine life, and they provide us with a fantastic window into history. Unless you stay outside the wrecks you dive, you enter restricted spaces with each penetration. Many diving agencies provide limited definitions concerning restrictions, however some divers find these to be confusing, as they are overly broad. With this in mind, consider the following next time you plan for a wreck dive with restrictions.
No Restrictions
At sites with no restrictions, two divers can easily pass through a space simultaneously, while sharing air either side by side or piggyback.
In spaces with no restrictions, there is nothing in the way to prevent divers from quickly and easily egressing from the wreck.
Restrictions
In spaces with restrictions, two divers are not easily able to pass through the space while sharing air side by side or piggyback. The only way to share air in a restricted space is to use a long hose.
In simple restricted spaces, a single diver is able to pass through with ease. There is nothing in the way to prevent a single diver from swiftly and easily egressing from the wreck.
Significant Restrictions
In spaces with significant restrictions, two divers cannot pass through while sharing air. The only way to share air may be via a long hose. In addition, a single diver cannot pass through with two cylinders in place. If sidemount diving, a single cylinder must be detached and pushed through ahead of the diver; if using back-mounted doubles, at least one must be detached and pushed through ahead of the diver.
In spaces with significant restrictions, there are significant impediments to swift, easy egress.
Major Restrictions
Spaces with major restrictions are impossible to pass through without removing both primary cylinders. The only way to share air may be via a long hose. If sidemount diving, both primary cylinders must be detached and pushed through ahead of the diver. Back-mounted cylinders must also be removed and pushed through ahead of the diver.
In spaces with major restrictions, there is a significant risk that entrapment will occur, and there are impediments that cause delayed egress from the wreck.
Extreme Restrictions
In areas with extreme restrictions, it is impossible for a diver to pass through with cylinders attached. A leashed trail of cylinders is required, or as an alternative, divers may “team pass” cylinders through the restriction. Progress through the area is typically very slow, and in many cases, air sharing is impossible because of the length of the restriction. Some extreme restrictions are several meters long, and siltout is a distinct possibility. Once inside the restricted space, the risk of entrapment is extreme, and emergency egress is nearly impossible. In addition, clear communication may not be possible.
Using extreme caution and careful planning can help you stay safe, no matter what type of restrictions are encountered. Remember always to dive within the boundaries of your training and experience, and listen to your inner voice. Many of the techniques required for getting through tight restrictions are taught in high-level technical courses. Increasing your knowledge by taking progressively more advanced courses is the best and safest way to address wreck diving challenges, including restrictions.