CFESA Gas Equipment and Safety 5 — Questions and Answers
Question 1: A commercial steamer is connected to a 3/4-inch gas supply line. The installer wants to verify adequate gas flow. Which tool measures actual flow in cubic feet per hour?
- Manometer
- Clamp meter
- Rotameter or in-line gas meter (Correct answer)
- Combustion analyzer
Correct answer: Rotameter or in-line gas meter
A rotameter or calibrated in-line gas meter directly measures volumetric gas flow rate in cubic feet per hour.
Question 2: During commissioning of a new gas convection oven, the CO reading in the flue gases is 800 ppm air-free. What action is required?
- No action; CO levels below 1,000 ppm are acceptable
- Adjust air shutter slightly and recheck
- Shut down the appliance immediately and do not operate until repaired (Correct answer)
- Increase gas pressure by 0.5 inches W.C.
Correct answer: Shut down the appliance immediately and do not operate until repaired
CO readings above 400 ppm air-free in flue gases indicate dangerous incomplete combustion; the appliance must be shut down and repaired before use.
Question 3: What is the purpose of a drip leg (dirt pocket) installed on a gas supply line to commercial equipment?
- To regulate gas pressure before it enters the appliance
- To trap condensate, scale, and debris before they reach the gas valve (Correct answer)
- To measure the static gas pressure upstream of the appliance
- To provide a shutoff point during servicing
Correct answer: To trap condensate, scale, and debris before they reach the gas valve
A drip leg is a vertical pocket in the gas line that allows heavier contaminants and condensate to fall out before reaching sensitive gas valve components.
Question 4: A technician is replacing a gas valve on a commercial griddle. After completing the repair, what is the correct sequence before returning the unit to service?
- Purge the line, light the pilot, check for leaks, verify flame appearance (Correct answer)
- Light the pilot immediately, then test for leaks with the unit running
- Check for leaks, purge air from the line, then light the pilot
- Restore gas, check for leaks at connections, then purge and ignite
Correct answer: Purge the line, light the pilot, check for leaks, verify flame appearance
The correct sequence is to purge trapped air, establish the pilot, leak-test all connections, and then verify proper burner flame characteristics.
Question 5: Which type of gas pressure regulator maintains constant outlet pressure regardless of fluctuating inlet pressure within its rated range?
- Lockup-type regulator
- Line pressure regulator (Correct answer)
- Pressure-limiting regulator
- Back-pressure regulator
Correct answer: Line pressure regulator
A line pressure regulator (also called a service pressure regulator) is designed to deliver a steady outlet pressure despite varying upstream supply pressure.
Question 6: A gas technician detects gas odor inside a restaurant kitchen but cannot immediately locate the leak. What is the correct first action?
- Open windows and use a fan to ventilate before searching for the leak
- Evacuate the area and shut off the gas supply at the meter or main valve (Correct answer)
- Use an open flame to trace the source of the leak
- Call the gas utility and wait outside for their arrival
Correct answer: Evacuate the area and shut off the gas supply at the meter or main valve
When gas odor is detected and the leak cannot be immediately located, the area must be evacuated and the gas supply shut off at the meter or main valve to eliminate ignition risk.
Question 7: What is the maximum allowable pressure drop across the entire gas piping system of a commercial establishment under full-load flow conditions for natural gas, per most US codes?
- 0.5 inches W.C. (Correct answer)
- 1.0 inch W.C.
- 2.0 inches W.C.
- 3.5 inches W.C.
Correct answer: 0.5 inches W.C.
NFPA 54 and most local codes limit the total pressure drop in a low-pressure natural gas system to 0.5 inches W.C. from meter to appliance under maximum load.
CFESA Gas Equipment and Safety 5
A commercial steamer is connected to a 3/4-inch gas supply line.
The installer wants to verify adequate gas flow.
Which tool measures actual flow in cubic feet per hour?