Keeping the interior of the aircraft clean is just as important as maintaining a clean exterior surface. Corrosion can establish itself on the inside structure to a greater degree because it is difficult to reach some areas for cleaning. Nuts, bolts, bits of wire, or other metal objects carelessly dropped and neglected, combined with moisture and dissimilar metal contact, can cause electrolytic corrosion.
When performing structural work inside the aircraft, all metal particles and other debris should be cleaned up as soon as possible. To make cleaning easier and prevent the metal particles and debris from getting into inaccessible areas, a dropcloth can be used in the work area to catch this debris.
A vacuum cleaner can be used to pick up dust and dirt from the interior of the cockpit and cabin.
Aircraft interior present certain problems during cleaning operations. The following is taken from The National Fire Protection Association (NFPA) Bulletin #410F "Aircraft Cabin Cleaning Operation".
Basic to an understanding of the problem is the fact that aircraft cabin compartments constitute relatively small enclosures as measured by their cubic footage. This presents the possibility of restricted ventilation and the quick buildup of flammable vapor/air mixtures where there is any indiscriminate use of flammable cleaning agents or solvents. Within the same volume there may also exist the possibility of an ignition source in the form of an electrical fault, a friction or static spark, an open flame device, or some other potential introduced by concurrent maintenance work.
Wherever possible, nonflammable agents should be used in these operations to reduce to the minimum the fire and explosion hazards.
Types of Cleaning Operations
The principal areas of aircraft cabins which may need periodic cleaning are:
(1) Aircraft passenger cabin areas (seats, carpets, side panels, headliners, overhead racks, curtains, ash trays, windows, doors, decorative panels of plastic, wood or similar materials).
(2) Aircraft flight station areas (similar materials to those found in passenger cabin areas plus instrument panels, control pedestals, glare shields, flooring materials, metallic surfaces of instruments and flight control equipment, electrical cables and contacts, etc.).
(3) Lavatories and buffets (similar materials to those found in passenger cabin areas plus toilet facilities, metal fixtures and trim, trash containers, cabinets, wash and sink basins, mirrors, ovens, etc.).
Nonflammable Aircraft Cabin Cleaning Agents and Solvents
(1) Detergents and Soaps. These have widespread application for most aircraft cleaning operations involving fabrics, headliners, rugs, windows and similar surfaces that are not damageable by water solutions since they are colorfast and nonshrinkable. Care is frequently needed to prevent leaching of water soluble fire retardant salts which may have been used to treat such materials in order to reduce their flame spread characteristics.
(2) Alkaline Cleaners. Most of these agents are water soluble and thus have no fire hazard properties. They can be used on fabrics, headliners, rugs and similar surfaces in the same manner as detergent and soap solutions with only minor added limitations resulting from their inherent caustic character which may increase their efficiency as cleaning agents but result in somewhat greater deteriorating effects on certain fabrics and plastics.
(3) Acid Solutions. A number of proprietary acid solutions are available for use as cleaning agents. They are normally mild solutions designed primarily to remove carbon smut or corrosive stains. As water based solutions, they have no flash point but may require more careful and judicious use not only to prevent damage to fabrics, plastics, or other surfaces but also to protect the skin and clothing of those using the materials.
(4) Deodorizing or Disinfecting Agents. A number of proprietary agents useful for aircraft cabin deodorizing or disinfecting are nonflammable. Most of these are designed for spray application (aerosol type) and have a nonflammable pressurizing agent but it is well to check this carefully as some may contain a flammable compressed gas for pressurization.
(5) Abrasives. Some proprietary nonflammable mild abrasive materials are available for rejuvenating painted or polished surfaces. They present no fire hazard.
(6) Dry Cleaning Agents. Perchlorethylene and trichlorethylene as used at ambient temperatures are examples of nonflammable dry cleaning agents. These materials do have a toxicity hazard requiring care in their use. Fire retardant treated materials may be adversely affected by the application of these agents as is true of the water soluble agents.
Flammable and Combustible Agents
(1) High Flash Point Solvents. Specially refined petroleum products, first developed as "Stoddard Solvent" but now sold under a variety of trade names by different companies, have solvent properties approximating gasoline but have fire hazard properties similar to those of kerosene as commonly used (not heated). Most of these are stable products having a flash point from 100° F to 140° F with a comparatively low degree of toxicity.
(2) Low Flash Point Solvents. Class I (flash point at below 100° F) flammable liquids should not be used for aircraft cleaning or refurbishing. Common materials falling into this "Class" are acetone, aviation gasoline, methyl ethyl ketone, naphtha and toluol.
In cases where it is absolutely necessary to use a flammable liquid, high flash point liquids (those having a flash point of 100° F or more) should be used.
(3) Mixed Liquids. Some commercial solvents are mixtures of liquids with differing rates of evaporation such as a mixture of one of the various naphthas and a chlorinated material. The different rates of evaporation may present problems from both the toxicity and fire hazard viewpoints and such mixtures should not be used unless they are stored and handled with full knowledge of these hazards and appropriate precautions taken.
Flammable liquids should be handled only in approved containers or safety cans appropriately labeled.
Fire Prevention Precautions
During aircraft cleaning or refurbishing operations where flammable or combustible liquids are used, the following general safeguards are recommended:
(1) Aircraft cabins should be provided with ventilation sufficient at all times to prevent the accumulation of flammable vapors. To accomplish this, doors to cabins shall be open to secure maximum advantage of natural ventilation. Where such natural ventilation is insufficient under all conditions to prevent the accumulation of flammable vapors, approved mechanical ventilation equipment shall be provided and used. The accumulation of flammable vapors above 25 percent of the lower flammability limit of the particular vapor being used, measured at a point five feet from the location of use, shall result in emergency revisions of operations in progress.
(2) All open flame and spark producing equipment or devices that might be brought within the vapor hazard area should be shut down and not operated during the period when flammable vapors may exist.
(3) Electrical equipment of a hand portable nature used within an aircraft cabin shall be of the type approved for use in Class I, Group D, Hazardous Locations as defined by the National Electrical Code.
(4) Switches to aircraft cabin lighting and to the aircraft electrical system components within the cabin area should not be worked on or switched on or off during cleaning operations.
(5) Suitable warning signs should be placed in conspicuous locations at aircraft doors to indicate that flammable liquids are being or have been used in the cleaning or refurbishing operation in progress.
Fire Protection Recommendations
During aircraft cleaning or refurbishing operations where flammable liquids are used the following general fire protection safeguards are recommended:
(1) Aircraft undergoing such cleaning or refurbishing should preferably be located outside of the hangar buildings when weather conditions permit. This provides for added natural ventilation and normally assures easier access to the aircraft in the event of fire.
(2) It is recommended that during such cleaning or refurbishing operations in an aircraft outside of the hangar that portable fire extinguishers be provided at cabin entrances having a minimum rating of 20-B and, at minimum, a booster hoseline with an adjustable water spray nozzle be available capable of reaching the cabin area for use pending the arrival of airport fire equipment. As an alternate to the previous recommendations a Class A fire extinguisher having a minimum rating of 4-A plus or a Class B fire extinguisher having a minimum rating of 20-B should be placed at aircraft cabin doors for immediate use if required.
NOTE 1: All purpose (dry chemical) type extinguishers should not be used in situations where aluminum corrosion is a problem.
NOTE 2: Portable and semiportable fire detection and extinguishing equipment has been developed, tested and installed to provide protection to aircraft during construction and maintenance operations. Operators are urged to investigate the feasibility of utilizing such equipment during aircraft cabin cleaning and refurbishing operations.
(3) Aircraft undergoing such cleaning or refurbishing where the work must be done under cover should be in hangars equipped with automatic fire protection equipment.
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