(9)  
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.

(10)
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.

(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 used in the fuel tank are a health and fire hazard. Use the correct protective equipment for the solvent that is used. Protective equipment includes: respirators, face and eye protection, protective clothes, gloves etc.

(e)  
Keep the amount of solvents that are used 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

500 
May 01/98  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  28-10-0 Page 209 

500 
28-10-0 Page 210  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  May 01/98 

500 Tank Rhine Air Ventilation Equipment Feb 1/95 Figure 203A Page 210A/210B BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

wiper, put the wiper in a polyethylene bag or remove the wiper from the airplane. This will keep the solvent vapor to a minimum.
(f)  
Powered tools must be air driven.

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

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

(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 an 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.

(4)  
The fuel tank must be in a health-safe condition before you can go into the fuel tank without a breathing-air supply. When the fuel tank is in a health-safe condition, at a minimum, it is recommended that a half-mask respirator with an organic vapor filter be used. It is necessary to have a good flow of air through the fuel tank to get a health-safe condition. The air must flow continuously during the fuel tank entry procedure.

(5)  
Hydrocarbon fuels that touch the skin can remove protective oils. Without protective oils, the skin can become dry, chapped, cracked or possibly become infected. If a person breathes too much fuel vapor, the person can become dizzy, get a headache or lose his or her coordination. Jet fuel is composed of many different kinds of hydrocarbon molecules. Exposure to some of these molecules for a long time is known to cause cancer.

(6)  
Vapors from fuel or other materials (solvents etc.) used for fuel tank maintenance can replace oxygen from a confined area such as a fuel tank or dry bay. If a person goes into a confined area that contains fuel vapor (or other vapors) without a breathing-air supply, the person may not get enough oxygen. This may cause unconsciousness or death. Make sure the environment is continuously monitored with an approved combustible gas indicator.

(7)  
No one is allowed to go into or remain in a fuel tank if:

(a)  
the flammable vapor concentration is more than 10% of the lower explosive limit

(b)  
the oxygen content of the fuel tank is below 19.5% or above 23.5; 
　
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