S 912-404

 (5)  
Equipment used to ventilate the fuel tanks or provide warm or cool air must not be turned off with the air duct in the fuel tank. The fuel vapor from the fuel tank can enter the air duct and cause an explosion at the motor. Make sure the blower is on before you put the air duct in the fuel tank. Make sure the blower remains on until the air duct is removed from the fuel tank.

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747-400 MAINTENANCE MANUAL
 S 912-405
 (6)  
When you remove an air duct from the fuel tank or disconnect the air duct at the blower, turn the duct 180 degrees away from the purging area. This will stop the flow of fuel vapor into the air duct line.

 S 912-406

 (7)  
During fuel tank maintenance, make sure there is continuous mechanical ventilation. The fresh air flow from the ventilation equipment must maintain the oxygen levels between 19.5% and 23.5% by volume and the fuel vapor levels below 10% LEL (fire safe limit).

 S 912-407

 (8)  
Use a combustible gas indicator to monitor the environment inside the fuel tank. The indicator must be designed for Class I, Division 1 hazardous locations and calibrated for the correct type of jet fuel. The indicator must be securely attached to a ladder or stand at the fuel tank entry location. As an alternate procedure, you can take an additional combustible gas indicator into the fuel tank to monitor the environment where you will do the maintenance.

 S 912-408

 (9)  
Obey these precautions for equipment used to do maintenance in the fuel tanks:

 (a)  
Only use approved non-static plastic containers with rounded corners to hold tools and supplies.

 (b)  
Keep all sharp edged tools in the container at all times when not in use. Sharp edged tools can cause damage to equipment and sealant.

 (c)  
Only use BMS 15-5 wiping materials in open fuel tanks. When you wipe up fuel in the fuel tank, use clean cellulose sponges.

 (d)  
Solvents, sealants, or other materials used in the fuel tank can be a health and fire hazard. Use the correct protective equipment for the solvent or material that is used. Protective equipment includes: respirators, eye protection, protective clothes, gloves etc.

 (e)  
Keep the quantity of solvents that you use to a minimum. Only bring enough solvent in the tank to complete the maintenance. Apply the solvent to a clean wiper, not the airplane structure or sealant. After you finish with the wiper, put the wiper in a polyethlene bag or remove the wiper from the airplane. This will keep the solvent vapor to a minimum.

 (f)  
Powered tools must be air driven.

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747-400
MAINTENANCE MANUAL

 WARNING: ONLY USE SHOP AIR OR BOTTLED AIR AS THE SOURCE OF GAS TO
_______ POWER AIR DRIVEN EQUIPMENT. GASES OTHER THAN SHOP OR BOTTLED AIR CAN REMOVE OXYGEN FROM A CLOSED AREA. IF YOU GO INTO A CLOSED AREA WITHOUT ENOUGH OXYGEN, YOU CAN BECOME UNCONSCIOUS OR IT CAN KILL YOU.
 (g)  
Only use shop air or bottled air as a gas source for air-driven tools. Do not use nitrogen, oxygen, carbon dioxide (CO2) or any other non-air source of gas.

 F.
Purging and Fuel Tank Entry - Personnel Precautions (Fig. 202)

 S 912-409
 (1)  
Make sure the persons who will go into fuel tanks are approved persons for fuel tank entry.

 S 912-410

 (2)  
Make sure observers who will watch persons in the fuel tank(s) are approved as fuel tank entry observers.

 S 912-411

 (3)  
The fuel vapors in and from the fuel tank are explosive and hazardous to your health. The fuel tanks must be in a fire-safe condition when an initial fuel tank entry is made. You must wear an approved respirator with a breathing-air supply when you go into a fuel tank that is in a fire-safe condition. It is necessary to have a good flow of air through the fuel tank to get a fire-safe condition. The air must flow continuously during the fuel tank entry procedure.
　
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