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757
MAINTENANCE MANUAL

 ~............................................................................. | HEALTH-SAFE CONDITION | | | | A HEALTH-SAFE CONDITION OCCURS WHEN THE OXYGEN CONTENT IS A | | MINIMUM OF 19.5% TO A MAXIMUM OF 23.5% BY VOLUME AT SEA LEVEL, | | AND THE VAPOR CONCENTRATIONS ARE BELOW THESE PERMISSIBLE EXPOSURE | | LIMITS: | | | ............................................................................... | | Permissible Exposure Level | | | | Total Hydrocarbons TWA *[1]| Lower Explosive Level | | Fuel | (ppm) | (percent) | ............................................................................... |Aviation Gasoline | 300 | 1.0 | ...............................................................................
 |Jet A  |  |  |
 |Jet A-1  |  160  |  0.7  |
 |JP-5  |  |  |
 |JP-8  |  |  |

 2..................…..............................…...........................1
 *[1] TWA - Time Weighted Average
 S 912-217
 (8)  
Lower Explosive Limits (LEL):

 (a)  
The minimum concentration of flammable vapors in air below which propagation of flame does not occur on contact with a source of ignition.

 S 912-218
 (9)  
Permissible Exposure Level (PEL):

 (a)  
The time weighted average airborne concentrations of substances at which it is believed that nearly all workers may be repeatedly exposed 8 hours a day, 40 hours a week, without adverse health effects.

 NOTE: The PEL limits used in this procedure are the PEL limits
____ used by Boeing personnel during fuel tank entry. If the local PEL limits are more restrictive than the ones given in this procedure, use the equivalent local PEL limits.
 S 912-219
 (10)
 Purging or Purged (For Fuel Tank Entry):

 (a)  
Purging an aircraft fuel tank is defined as the removal of any fuel or fuel vapor that remains after the fuel tanks are sumped. A purged fuel tank contains a nonflammable atmosphere that can be maintained by mechanical ventilation.

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757 MAINTENANCE MANUAL
 S 912-220
 (11)
 Unwanted Sources of Ignition:

 (a)  
Unwanted sources of ignition include 1) Open flames (matches, cigarette lighters etc.) 2) Electrical equipment (lights, motors, sparks from engine
　
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