28-10-00
 ALL  ú ú 01 Page 208 ú Jul 15/97
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 S 912-315
 (8)  Do not use electrical test equipment which can cause sparks in a fuel tank.
 E. Purging and Fuel Tank Entry - Equipment Precautions
 S 912-317
 (1)  
All metal work platforms or stands used for entry into the fuel tanks or found within a 50-foot (15-meter) radius of an open fuel tank (before and after the fuel tank purging) must be bonded to the airplane and grounded to an approved earth ground.

 S 912-318

 (2)  
Before you use ventilation equipment make sure the blower or venturi is connected to the airplane ground. The ventilation blower or the venturi must be explosion-proof.

 S 912-319

 (3)  
Air ducts must be bonded to form a continuous electrical conductor, and grounded in at least one location to a static electrical ground.

 S 912-320

 (4)  
If you use the ventilation equipment to exhaust fuel vapors from the tank, static build-up on or in the air ducts can reach a level where a spark can ignite the vapors and an explosion can occur. The air ducts must be coated inside and out with a conductive coating and each section correctly bonded to each other. Air ducts made from vinyl fabric are not recommended because vinyl is an insulator of static charges. If the air duct uses a metal helical wire to create a non-collapsible duct, make sure the wire is permanently attached to a metal or conductive plastic connection on each end of the duct section.

 S 912-321

 (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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 28-10-00
 ALL  ú ú 02 Page 209 ú Mar 12/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 S 912-322
 (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 912-323

 (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 912-324

 (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 912-325

 (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.
　
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