Chapter 7. Special Problems 

700. MERCURY SPILLS/CORROSION DAMAGE. a. The presence of mercury and mercury salts in air cargo is a definite possibility. Loading, unloading, and general shifting of such cargo can and does result occasionally in damaged containers, cartons, electronic tubes, etc., with subsequent possible leakage of mercury on aircraft structure. b. Spillage of mercury or mercury compounds within an airplane requires immediate action for its isolation and recovery to prevent possible corrosion damage and embrittlement of aluminum alloy structural components, stainless steels (300 and 400 series), and unplated brass components such as cable turnbuckle barrels. c. Mercury, by the amalgamation process, can penetrate any break in the finish (anodize/alodine), paint, and seal coating of a metal structural component. Bright, polished, shining, or scratched surface will hasten the process, as well as moisture. Mercury or mercury compounds attack the metal grain boundaries and seriously embrittle and reduce the strength of parts. Corrosive attack of freshly scratched aluminum alloy is very rapid, and complete penetration of sheet material is known to occur within 3 or 4 minutes. d. Mercury is highly toxic and spreads very easily from one surface to another. It adheres to hands, shoes, clothes, tools, etc. The following precautions for mercury spills should be strictly followed:

(1) Avoid contact with surfaces suspected of being contaminated. Use wood or fiber sheets to support body while working in the area.

WARNING: DO NOT ATTEMPT TO PICK UP MERCURY BY HAND.

(2) Wear wing socks (shoe protectors) and protective (disposable) clothing in contaminated area to prevent scratching metal surfaces. Properly dispose of socks after use.

(3) Do not wear clothing used in contaminated areas on jobs in uncontaminated areas. Dispose of wing socks and protective clothing into unused metal container outside of aircraft. Contact the Waste Management Service or similar authority of the local State Health Department for instructions on proper disposal procedures for mercury.

(4) Have personal clothing cleaned. Wash shoes with soap and water. Clean all tools that have been used in contaminated area with steam or hot water and soap. Discard any drill bits used on mercury contaminated areas. Thoroughly clean vacuum cleaner, if used.

(5) Always wash thoroughly with soap and water after contacting mercury. Keep hands away from mouth. Do not eat, smoke, or blow nose without first washing your hands thoroughly.

(6) Appreciable amounts of mercury will vaporize at normal temperatures. A stagnant air will become dangerous to personal health.

WARNING: ALWAYS PROVIDE GOOD VENTILATION WHILE CLEANING MERCURY CONTAMINATED AREAS.

(7) Do not use cleaning aids such as solvents, solids, or polishes on contaminated area. Such materials may promote corrosion.

(8) If hands become contaminated with mercury while working with cleaning equipment, do not touch any exposed metal in surrounding area, as you may contaminate it.

e. Mercury spills, in some cases, have caused no adverse effects because of protective films of paint, dirt, grease, or oil. The fact that mercury spillage may not, in all cases, result in serious damage should not be relied on. Each instance of mercury or mercury compound spillage should be considered hazardous, and immediate action should be taken to safeguard the aircraft. Inspect for mercury and corrosion as follows:

(1) Determine point at which mercury was spilled. Remove any mercury on floor covering, and then remove covering.

(2) When mercury is found on floor, do not remove access/inspection plates, screws, rivets, bolts, etc., from floor. Any hole which is left open in the contaminated area of the floor may allow mercury to spread to structure underneath the floor.

(3) Inspect the metal floor, seat tracks, cargo rails, and adjacent structure for mercury and corrosion. Inspect skin and internal structure below point of spillage. Also inspect lowest point in fuselage below cargo compartment floor if mercury spill has occurred in cargo area. Mercury liquid will flow to lowest level.

(4) Inspect areas suspected of having mercury contamination using a 1Ox magnifying glass. If corrosion of aluminum has started there will be a light grayish "Christmas Tree" fuzz or gray powdery dust deposit, and severe structural damage may follow.

(5) If corrosion is evident and cleanup cannot be completed immediately, coat contaminated area with corrosion preventative compound or engine oil. This helps to slow down the corrosion rate and also helps to prevent spreading of mercury contamination.

(6) When mercury spills occur in lower cargo compartment, use a portable X-ray machine (if available) along the outside lower surface of the fuselage to check suspected hidden corrosion areas between the skin, stringers, and frames below the floor. Droplets of mercury will show on a radiograph as small white spots. Corrosion and embrittlement will appear as treelike forms completely penetrating a structural component.

(7) Inspect bronze/brass control cable turnbuckle barrels for mercury discoloration. Replace if slightest discoloration is detected.

f. Removal procedure and precautions necessary when mercury is spilled are:

WARNING: VACUUM AIR PASSING OVER THE MERCURY DEPOSITED IN THE GLASS CONTAINER PICKS UP MERCURY VAPORS AND EXHAUSTS THEN FROM THE VACUUM CLEANER. AVOID BREATHING MERCURY VAPORS.

CAUTION: AN AIR HOSE SHOULD NOT BE USED TO DISLODGE MERCURY FROM AIRCRAFT UNDER ANY CIRCUMSTANCES.

(1) Use a high capacity vacuum cleaner with a trap type glass container attached to the large vacuum hose. The size of the pickup hose from the container should be about 1/4 inch in diameter to increase the amount of suction applied to the mercury. Due to the weight of mercury, the container will catch the mercury before it can enter the vacuum cleaner hose.

(2) An all rubber storage battery water syringe, or a medicine dropper, may be used to remove mercury if the trap type glass container and vacuum cleaner are not available. Cellulose tape may be used to pick up very tiny particles of mercury.

(3) General cleanup and inspection (using equipment available) should be made immediately after spillage occurs or is detected.

701. CORROSION PROTECTION FOR AGRICULTURAL AIRCRAFT.

a. General.

Practically all chemicals used in dusting and spraying operations are corrosive by nature and hasten deterioration of fabric, metal, and wood. It is essential to safe operation that precautions be taken to prevent corrosion and deterioration of wood, metal, and fabric. Cleanliness of the airplane is one of the most important precautions of all. If it were practicable and feasible to clean the airplane thoroughly; that is, give it a thorough dry washing inside and out after each day's work, probably no special corrosive preventative measures would be necessary.

b. Precautions.

Since thorough daily cleaning is not practicable, the following precautions should be taken:

(1) All fittings and metal structures should be covered with two coats of epoxy primer, a heavy preservative, conforming to MIL-C-16173, grade 2 (paralketone), or equivalent material. This coating should be applied to items such as wing root fittings, wing strut fittings, control surface hinges, horns, mating edges of fittings and attach bolts, etc.

(2) Nonstainless steel control cables should be coated with paralketone or equivalent protective coating, or should be replaced with corrosion resistant cables.

(3) Periodic inspection of all critical portions of the aircraft structure should be made. Structural parts showing corrosion should be cleaned and refinished if the corrosion attack is superficial. If the part is severely corroded, it should be replaced.

(4) Experience has shown that additional access openings, to permit ready inspection of lower and rearward portions of the fuselage, are particularly desirable.

(5) Provide additional drainage and ventilation for all interiors to prevent collection of moisture.

(6) At the time of recovering, both metal and wood airplane structural members should be coated with epoxy primer (two coats), followed by dope proof paint or wrapping with cellophane tape.

(7) Spray interiors of metal covered wings and fuselages with an adherent corrosion inhibitor.

(8) Wash exterior surfaces with clear fresh water at least once a week. Interior surfaces should also be washed, taking care to prevent damage to electrical circuits or other items subject to malfunctioning due to moisture.

(9) Opening in the wings, fuselage, and control surface members, such as tail wheel wells, openings for control cables, etc., should be sealed as completely as possible to prevent entry of dust or spray.

702 - 799 RESERVED.