The reading on the combustible gas indicator, shown in the illustration, is obtained by burning the vapor sample within the instrument. How is the flame prevented from igniting the vapor within the space being tested? See illustration SF-0003.
• Combustible gas indicator (CGI) design and how it samples vapors from a confined space • How flashback from a flame or hot element can travel back through piping or hoses • The specific components labeled in the illustration, especially anything called flash back arrestor or similar
• Look closely at the airflow path from the space being tested to the combustion chamber—what parts does the sample pass through before it reaches the hot filament or flame? • Which of the listed answer choices actually matches a clearly labeled safety component in the drawing, rather than just sounding reasonable in theory? • Ask yourself: if the flame is inside the instrument, what physical feature must be present to stop that flame front from traveling backward into the sampling hose?
• Identify any part in the illustration specifically labeled as Flash Back Arrestor or Flame Arrester and note its location • Verify whether the sampling hose length/diameter or internal baffles are shown or labeled as safety features, or if they’re just structural parts • Match the wording of the answer choices to the exact terminology used in the illustration’s labels; pay close attention to inlet and outlet protection around the combustion area
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