One of the key tasks in using rebreathers is filling the canister with granular absorbent. While the actual techniques for filling may vary somewhat based on manufacturer recommendations for the type of scrubber canister being used, some safety precautions are universal. We will look at some of the concerns with canister filling, and methods to reduce the risks of handling absorbent materials while filling canisters.

When breathing, divers expire carbon dioxide (CO2), which is produced as a byproduct of respiration. CO2 in elevated partial pressures is detrimental, leading to increased susceptibility to oxygen toxicity, headaches, unconsciousness, and a host of other problems. The purpose of the scrubber canister is to remove the CO2 from the breathing loop. Because CO2 is slightly acidic, a strong alkaline material is utilized to neutralize the CO2, and remove it from the gas circulating in the system.

The alkaline materials typically used include an array of various hydroxides. Sodium hydroxide, lithium hydroxide, barium hydroxide, calcium hydroxide, magnesium hydroxide and other chemicals are used in common scrubbing compounds. While they all have different properties and benefits for use in rebreathers, they share the common attribute of being relatively friable, and will produce dust when mechanically agitated, as occurs during transport. Dust, because of its smaller size and greater surface area, is much more volatile than larger absorbent granules and migrates around the system more easily.

Another property they share is that they are strongly alkaline. When strong alkalis come into contact with body tissues, injuries may result. Let's look at the types of injuries that can result, and how to prevent them while filling rebreather canisters.

The first problem is with skin contact. Alkalis are capable of causing chemical burns upon contact. The severity and speed with which burns may occur are determined by the chemicals in the compound, how wet the skin is, and individual sensitivity. To avoid skin burns, proper protective clothing should be worn while filling canisters. Long pants, long sleeves, and closed shoes will prevent spillage and blown dust from coming into contact with your skin. Wearing disposable gloves will protect the hands while handling absorbents. This is particularly necessary if you have any minor cuts or scrapes, as you will find it very painful should absorbent contact any lesion. If you are filling outside, stand upwind of where you are pouring the absorbent, so that dust is not blown onto you. When done filling, remove and wash the clothing to clean any residual material, and prevent secondary contact by touching the contaminated clothes.

Eye protection is also important. Dust may be easily blown into the eyes during the filling process, causing chemical burns of the eyes. Wear protective glasses with side shields to minimize any such contact. Again, standing upwind while filling the canister will minimize dust being blown into the eyes. Maintain sufficient distance from the canister while filling to minimize problems.

Dust inhalation is a major problem. Inhaling absorbent dust can cause chemical burns in the upper airway and lungs. This can lead to Adult Respiratory Distress Syndrome, a very serious malady that requires hospitalization to treat. Inhaling small quantities of dust can cause irritation and discomfort, which can last several days to a week after exposure. Wearing a paint mask will minimize dust inhalation during the filling process.

Dust included in the canister can cause similar injuries during the dive. The best way to prevent this problem is to minimize the amount of dust included with the granular absorbent as you fill the canister. One way to do this is to fill outside, in a breeze. Pour the absorbent from some distance above the canister, allowing the dust to blow to the side while filling (similar to separating wheat from chaff).

If there is no breeze, another technique is to set up a fan outdoors. Place the canister in front of the fan, and use the fan to create a breeze. Then fill the canister as described above. Remember to stand to the side, so that the dust is not blown onto you.

Avoid contact with water while filling. Dry your hands before handing the absorbent, keep all parts on a dry surface, and wear dry clothing. Since even heavy perspiration may increase the potential for a problem, try to work in a comfortable environment. Be especially wary of working on open boat decks, where spray and splash may affect the work area.

Finally, remember that it is not just the person actively filling the canister who is at risk. Any people in the immediate vicinity may be exposed, and can have all of the same problems. If others are working in the same area as you, respect their health, and inform them of your activities. Ask them to move, or wear the proper protective equipment as well.

Following the above procedures will reduce, not eliminate, the chances for a chemical burn problem while handing typical absorbents used in rebreathers. There are many potential ways to expose yourself and others, and one cannot possibly cover all of them in one short article. You also need to exercise common sense. So think about what you are doing, and do what you can to diminish other risk factors.

Safe diving!