Diving with a cutting tool is just common sense
- Seas and lakes can contain discarded fishing lines and nets.
- Divers can get caught in their own dive lines and spear gun lines.
- Entangled sea creatures may also need help.
Fixed Blade Knife
These are the original dive safety knives. Modern improvements include
- titanium or "really stainless" stainless steels
- built-in line cutters (like zip knives or gut hooks)
- blunt tips for safety (knives with a sharp tip can also be blunted with a few strokes on a brick)
- single piece knives (metal handle) for easy cleaning (salt water can't collect between the tang and the handle)
- serrated blades for cutting ability, including cutting thin wire
Thick blades (a quarter of an inch thick) are strong. They can be used to break thin wire by twisting a loop of wire like a tourniquet.
Lanyards are essential to prevent loss of the knife. In an emergency, a panicked diver could easily fumble and drop the knife.
Titanium Knives
Titanium knives are popular because they are totally impervious to rust. Beta titanium is better, harder than the normal alpha-beta titanium.
However, titanium is
- Expensive
- Relatively soft, not good for cutting wire
- Difficult to sharpen, need diamond coated stones
Modern steels such as H1, X15; and cobalt alloys such as talonite and dendritic cobalt are good alternatives. They also do not rust, and are harder than titanium.
Zip Knife / Line Cutter
These are simple cutters. A recessed razor blade allows only thin ropes to be cut, and keeps fingers out. Some models allow the blade to be replaced.
Variations are sold as safety seat-belt cutters (for cars) and safety paper cutters (for home use).
Advantages
- Cheap
- Small, light
- Safe, only thin objects can be cut
Disadvantages
- Not suitable for cutting wire
- Not suitable for slashing kelp
Diving knives are banned in some locations to reduce vandalism (carrying a knife anywhere, in some countries, can be punished by imprisonment). Zip knives are less objectionable. Even if confiscated, they only cost a few dollars.
EMT Shears
These are small, angled scissors with blunt noses. They look like the paper scissors used by children. They are used by rescue personnel to cut away clothing from injured people.
Advantages
- Cheap
- Small, light
- Safe
- Can cut thin wire
Disadvantages
- Hinge can break if over stressed
Similar to zip knives, they may be allowed in locations where knives are prohibited.
Attachment Locations
The classic location for a dive knife is on the inside of the calf (not on the outside, to reduce snagging).
Other popular locations are
- the upper arm
- the front of the chest
- the buoyancy compensator
Safety Practice
Knife drills should be carried out regularly to ensure that the equipment can be used as expected. Regular practice also helps prevent panic in a real emergency. Practice items include
- Cutting different types of fishing line, rope, wire (cut away from the body). Use rags to simulate kelp.
- Cutting line tied to the left foot, right foot, left hand, right hand (a loop can be used to simulate a snagged line).
- Removing the knife and cutting with only the left hand, then only the right hand.
- Dropping the knife and retrieving it with the lanyard.
- Removing and using the dive buddy's knife (dive buddies should know where their partner's knives are located).
- Banging on the air tank with a blunt part of the knife to attract attention.
- Repeating all of the above, with eyes closed (to simulate poor visibility).
The Best Diving Knife
Experienced divers will have different opinions on types of knives, and where to wear them.
However most will agree that a cutting tool is essential for dive safety, and two or three are even better.
