GFIA Gas Systems and Appliances - 8 hr - gaiaai.orggaiaai.org/Files/Other/Gas Systems and Appliances.pdf · 7/21/2017 2 Topics Introduction to gas systems and appliances • Gas Systems

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Presented by:Jeremy Neagle, P. E.Electrical Engineer

Georgia Fire Investigator’s Association ‐ 2017Savannah, GA

[email protected] 202‐648‐6215

Objectives

• Familiarization with basic gas system components and select gas appliances

• Understanding of failure modes of gas system components and select gas appliances

• Understanding of gas appliance examination

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Topics

Introduction to gas systems and appliances

• Gas Systems

– Basics

– Natural Gas vs. Propane

– Pressure regulators

– Gas meters

– Valves

• Gas Appliances

– Water heaters

– Furnaces

– Dryers

– Ranges

• Bonus– Portable LP systems– Oil burners– Electric water heaters– High‐efficiency water heaters– Tankless/Point‐of‐use water heaters– Hybrid water heaters

Why is this important???

• NFPA 1033 1.3.7

The investigator shall have and maintain at a minimum an up‐to‐date basic knowledge of the following topics beyond the high school level:(1) Fire science(2) Fire chemistry(3) Thermodynamics(4) Thermometry(5) Fire dynamics(6) Explosion dynamics(7) Computer fire modeling(8) Fire investigation(9) Fire analysis(10) Fire investigation methodology(11) Fire investigation technology(12) Hazardous materials(13) Failure analysis and analytical tools(14) Fire protection systems(15) Evidence documentation, collection, and preservation(16) Electricity and electrical systems

• NFPA 1033 4.2.8

Inspect the performance of building systems, including detection, suppression, HVAC, utilities, and building compartmentation, given standard and special equipment and tools, so that a determination can be made as to the need for expert resources, an operating system's impact on fire growth and spread is considered in identifying origin areas, defeated and/or failed systems are identified, and the system's potential as a fire cause is recognized.

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The Basics…

• NFPA 921, Chapter 10 – Building Fuel Gas Systems

More Advanced…

NFPA 54 NFPA 58

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Gas Properties

‐ American Gas Association www.aga.org

Natural Gas

Gas, NaturalA naturally occurring mixture of hydrocarbon and nonhydrocarbon gases found

in porous geologic formations beneath the earth's surface, often in association with petroleum. The principal constituent is methane. 1. Dry. Gas whose water content has been reduced by a dehydration process. Gas containing little or no hydrocarbons commercially recoverable as liquid product. Specified small quantities of liquids are permitted by varying statutory definitions in certain states. 2.Liquefied (LNG). See LIQUEFIED NATURAL GAS. 3. Sour. Gas found in its natural state, containing such amounts of compounds of sulfur as to make it impractical to use, without purifying, because of its corrosive effect on piping and equipment. 4.Sweet. Gas found in its natural state, containing such small amounts of compounds of sulfur that it can be used without purifying, with no deleterious effect on piping and equipment. 5. Wet. Wet natural gas is unprocessed natural gas or partially processed natural gas produced from strata containing condensable hydrocarbons. The term is subject to varying legal definitions as specified by certain state statutes. (The usual maximum allowable is 7lbs./MMcfwater content and .02 gallons/Mcf of Natural Gasoline.)

Gas Properties

Natural Gas

Gas, NaturalA naturally occurring mixture of hydrocarbon and nonhydrocarbon gases found

in porous geologic formations beneath the earth's surface, often in association with petroleum. The principal constituent is methane. 1. Dry. Gas whose water content has been reduced by a dehydration process. Gas containing little or no hydrocarbons commercially recoverable as liquid product. Specified small quantities of liquids are permitted by varying statutory definitions in certain states. 2.Liquefied (LNG). See LIQUEFIED NATURAL GAS. 3. Sour. Gas found in its natural state, containing such amounts of compounds of sulfur as to make it impractical to use, without purifying, because of its corrosive effect on piping and equipment. 4.Sweet. Gas found in its natural state, containing such small amounts of compounds of sulfur that it can be used without purifying, with no deleterious effect on piping and equipment. 5. Wet. Wet natural gas is unprocessed natural gas or partially processed natural gas produced from strata containing condensable hydrocarbons. The term is subject to varying legal definitions as specified by certain state statutes. (The usual maximum allowable is 7lbs./MMcfwater content and .02 gallons/Mcf of Natural Gasoline.)

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Gas Properties

• Natural Gas

NFPA 921: 2014 10.2.1.2 Undiluted natural gas is lighter than air. Depending on the exact composition, it has a specific gravity (air) (vapor density) of 0.59 to 0.72, a lower explosive limit (LEL) of 3.9 percent to 4.5 percent, and an upper explosive limit (UEL) of 14.5 percent to 15 percent. A flammable mixture has a vapor density 0.96 to 0.98. Its ignition temperature is 482°C to 632°C (900°F to 1170°F).

Residential natural gas systems typically operate at 4.0 – 10.0 in. w.c.

Gas Properties

‐ Liquified Petroleum Gas Code (NFPA 58)

LP Gas

Liquified Petroleum Gas (LP‐Gas). Any material having a vapor pressure not exceeding that allowed for commercial propane that is composed predominantly of the following hydrocarbons, either by themselves (except propylene) or as mixtures: propane, propylene, butane (normal butane or isobutene), and butylenes.

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Gas Properties

LP Gas

Liquified Petroleum Gas (LP‐Gas). Any material having a vapor pressure not exceeding that allowed for commercial propane that is composed predominantly of the following hydrocarbons, either by themselves (except propylene) or as mixtures: propane, propylene, butane (normal butane or isobutene), and butylenes.

Gas Properties

• Propane (LP Gas)

NFPA 921: 2014, 10.2.2.2 Undiluted propane gas is heavier than air. It has a specific gravity (air) (vapor density) of approximately 1.5 to 2.0, a lower explosive limit (LEL) of 2.15 percent, and an upper explosive limit (UEL) of 9.6 percent. A flammable propane–air mixture has a vapor density of 1.01 to 1. 0. Its ignition temperature is 493°C to 604°C (920°F to 1120°F).

Residential propane gas systems typically operate at 11.0 – 14.0 in. w.c.

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Gas Properties

• Natural gas ≈ 52337 kJ/kg ≈ 42.9 MJ/m3

• Propane ≈ 50340 kJ/kg ≈ 95.9 MJ/m3

Volumetric Heating Values are based on standard temperatures and pressure of dry gas ‐ 60oF and 14.73 psi.

The energy content of propane is more than twice that of natural gas.

Gas Properties

Methane:

• CH4 + 2O2 → CO2 + 2H2O + energy

Incomplete combustion: When combined with insufficient air or oxygen, it partially burns into carbon monoxide (CO) gas and water vapor.

• 2CH4 + 3O2 → 2CO + 4H2O + energy

Propane:

• C3H8 + 5O2 → 3CO2 + 4H2O + energy

Incomplete combustion: When combined with insufficient air or oxygen, it partially burns into carbon monoxide (CO) gas and/or carbon soot and water vapor.

• 2C3H8 + 9O2 → 4CO2 + 2CO + 8H2O + energy

Or

• C3H8 + 2O2 → 3C + 4H2O + energy

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Gas System Basics – Natural Gas Systems


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Gas System Basics – LP Gas Systems

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Pressure Regulators

Theory of operation

• Gas flow through the regulator is controlled by a valve

• The valve is connected to a rubberized diaphragm

• The diaphragm has a spring pushing on one side and gas pressure pushing on the other side.

• Gas pressure fights against spring pressure to ‘regulate’ valve position

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Pressure Regulators

Pressure Regulators

• Pressure Relief

– In the event of excess pressure, a relief valve opens to vent the pressure past the diaphragm and out of the regulator.

– Vent size is typically limited by a small orifice in the vent path.

– Some local codes require piping of the vent to a specific location.

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Pressure Regulators

• Failure modes

– Diaphragm failure

Catastrophic failure of the rubberized diaphragm results in a failure of the regulator’s ability to counteract spring pressure.

Result: Regulator valve opens and allows high pressure gas to enter the downstream piping. High pressure gas flows out the regulator vent to the atmosphere.

Pressure Regulators

• Failure modes

– Blocked vent

An atmospheric vent blocked by snow/ice, insects or other debris prevents the diaphragm from moving freely and results in a failure of the regulator’s ability to properly regulate pressure.

Result: Regulator valve may not open or close properly in response to gas demand, causing high or low gas pressures in the downstream piping.

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Pressure Regulators

• Failure modes

– Valve seat leakage

Caused by age/wear, debris or other defects, a leaking regulator valve seat allows gas to seep past the valve while in the closed position.

Result: The regulator’s inability to completely shut off the flow of gas allows high pressure gas to enter the downstream piping. Pressure builds up gradually and will be vented to the atmosphere by the regulator’s relief valve. High pressure gas intermittently ‘burps’ out the regulator vent to the atmosphere.

Pressure Regulators

• Testing

– Flow

Flow testing of a pressure regulator is performed to verify that it properly regulates downstream gas pressure while gas is flowing through the system.

Method: Outlet pressure is measured while a nominal amount of gas is flowing through the system. A faulty pressure regulator may result in the outlet pressure fluctuating outside normal values.

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Pressure Regulators

• Testing

– Lockup

Lockup testing of a pressure regulator is performed to verify valve seat integrity.

Method: A pressure regulator is pressurized with no demand (flow), and outlet pressure is measured. A failed valve seat will result in the outlet pressure creeping up and gas ‘burping’ from the regulator vent.

Gas Meters

• Types

– Diaphragm

– Rotary (Roots)

– Inferential (Turbine, Orifice)

• Theory of operation

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Gas Meters

• Diaphragm meters

Gas Meters

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Gas Meters

• Diaphragm meter operation

Gas Meters

• Temperature compensation

– Some gas meters are ‘Temperature Compensated’, meaning that they automatically account for differences in temperature when measuring gas.

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Gas Meters

• Diaphragm meter operation

Gas Meters

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Gas Meters

• Rotary meter operation

Gas Meters

• Inferential meter operation

– Inferential meters do not measure gas volume directly and ‘infer’ the measurement by measuring flow velocity (as with a turbine meter), or differential pressure (as with an orifice meter).

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Gas Meters

• Failure modes

There are various failure modes for gas meters…but the typical result is an incorrect bill.

Leakage from seals is generally the greatest fire/explosion concern.

Gas Meters

• Smart Meters

Called Automated Meter Readers (AMR), Encoder Receiver Transmitters (ERT) or Smart Meters, these meters incorporate an electronic device which reads the meter at a regular interval

Meter readings may be stored in the meter’s memory, transmitted to the utility company, or read by a utility company representative in a passing vehicle.

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Gas Meters

• Testing

Various tests exist to measure the flow rate of gas.

Utility companies perform tests, called ‘proving a meter’ to verify the accuracy of their meters.

A building’s gas meter can be used to test for leaks in the gas system.

– Clock test

Leak Testing

• Various tests exist to check a gas system for leaks and to measure the flow rate of the leak.

– Clock test

– Pressure drop test

– Soap bubble test

– Gas detector surveys

– Bar hole tests

– Odorant tests

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Leak Testing

• Clock Test

– The structure’s gas meter is used to measure the leak rate.

1. All appliances are turned off

2. Gas is turned on and an initial meter reading is taken

3. After a period of time, a final meter reading is taken

4. The difference between the two readings and the elapsed time is used to calculate the volumetric flow rate

Leak Testing

• Pressure Drop Test

1. All appliances are turned off

2. Pressure is applied to the system

3. The gas supply is turned off and the pressure in the system monitored for a period of time

4. A pressure drop over a period of time indicates that there is a leak somewhere in the system

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Leak Testing

• Soap Bubble Test

1. A soap solution is applied to potential leak sources

2. Look for bubbles indicating a leak is present

Leak Testing

• Gas Detector Survey

– A combustible gas detector/indicator is used to ‘sniff’ around potential leak sources to indicate if a leak is present

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Leak Testing

• Bar Hole Test

1. A series of holes are made in the ground with a metal bar

2. A sampling tube is inserted into the hole and a combustible gas detector is used to measure for combustible gases in the soil

Leak Testing

• Odorant Test

– A specialized odorant test instrument is used, along with human confirmation that odorant is present in the gas

– Alternately, gas samples can be drawn through a colorimetric (stain) tube or sent to a laboratory for analysis

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Leak Testing

• Gas volume measurement is dependent on both pressure and temperature.

• Some gas meters may be temperature and/or pressure compensated to account for fluctuations in supply pressure or ambient temperature.

Leak Testing

• Testing

– Testing can be conducted with the designed gas (natural gas, propane, etc.) or a non‐flammable gas may be used.

• In the latter case, the results may need to be corrected to account for different gas properties.

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Valves

Valves

• There are a number of different types of valves used in gas systems and appliances

– Ball valves

– Plug valves

– Gate valves

– Globe valves

– Needle valves

• Various forensic techniques can be used to determine their position

– Examination of external features (handle, stem, stops, etc.)

– X‐ray/CT

– Borescope

– Sectioning

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Valves

Valves

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Valves

Valves

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Valves

Example – Gas Range Valve

Appliances

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Appliances

Gas Properties

• Natural gas ≈ 52337 kJ/kg ≈ 42.9 MJ/m3

• Propane ≈ 50340 kJ/kg ≈ 95.9 MJ/m3

Volumetric Heating Values are based on standard temperatures and pressure of dry gas ‐ 60oF and 14.73 psi.

The energy content of propane is more than twice that of natural gas.

…and propane systems operate at about twice the pressure of natural gas systems!

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Natural Gas – LP Conversions


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• Conversion kits may be included with or purchased for most gas appliances.

– Pressure regulators

– Gas orifices

• Conversion kits must be installed by qualified individuals in accordance with the manufacturer’s instructions!

Combustion Air

• Gas appliances need adequate combustion air to properly burn the fuel gas

• Things to consider:

– Appliances in small rooms or closets

– Multiple gas appliances in a room operating simultaneously

Codes and appliance instructions specify how much combustion air is required

…or if enclosed, the minimum room size or vent area size to a larger space

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Combustion Air

Flame Characteristics

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Appliances

• Water Heaters ‐Who makes what???

• A.O. Smith– State

– Whirlpool

– American Water Heaters

– Reliance Water Heaters

– US Craftmaster Water Heaters

• Rheem– GE

– Ruud

– Vanguard

– Servi‐Star

– True‐Value

– Montgomery‐Ward

• Bradford‐White

Appliances

• Water Heaters

– Old school…open combustion chamber, atmospheric vent

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Appliances

• Water Heaters

– Old school…open combustion chamber, atmospheric vent• May or may not be fitted with a draft hood

Draft hoods ensure that the burner flame is not affected by what is going on with the vent system

Appliances

• Water Heaters

– Old school…open combustion chamber, atmospheric vent

Open combustion chamber design may allow flames to ‘roll out’ of combustion chamber

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Appliances

• Water Heaters

– New school…Power vent

Appliances

• Water Heaters

– New school…Power vent

– Exhaust fan dilutes hot exhaust gases with surrounding room air• Vent system may be PVC as opposed to metal

• Longer horizontal runs and more bends are permitted in vent system

– Burner interlocked with exhaust fan

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Appliances

• Water Heaters

– New school…Flammable Vapor Ignition Resistant (FVIR)

Appliances

• FVIR

– ‘Sealed’ combustion chamber

– Inlet air flame arrestor

– ECO/TCO or TRD

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Appliances

• Thermal Release Device (TRD)

Appliances

• Flammable vapor sensor

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Appliances

• Gas Control Valves

– Typically control pilot and main burner gas

– Typically include a 100% safety shutoff system

– May incorporate ignition system

Appliances

• Millivolt Safety Systems

– A thermocouple or thermopile is placed in the pilot flame

– When the flame is ignited, the heated thermocouple generates a small voltage (mV)

– This small voltage is connected to an electromagnet that is used to hold a safety valve open

– When the pilot flame goes out, the thermocouple cools, the voltage drops and the magnet releases the safety valve stopping the flow of gas to the pilot and main burners (100% shutoff)

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Appliances

• Water heater failure modes

Improper combustion!!!

– Improper fuel

– Blocked inlet/inadequate combustion air

– Blocked vent/downdrafts

Control failures

– Leaking main/pilot burner valve (‘Candling’)

– Delayed ignition

Operator error

– Combustibles too close

– Flammable vapors entering combustion chamber

Appliances

• Delayed ignition

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Appliances

• Delayed ignition

Appliances

• Water heater examination

– Gas supply

– Gas control valve

– Burner assembly

– Combustion chamber

– Flue & baffle

– Exhaust vent

– FVIR safety features

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Appliances

Water Heater Case Study

Appliances

• Gas Ranges

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Appliances

• Ranges ‐ Terminology

– Slide‐in

– Free standing

– Cooktop (Drop‐in)

– Wall ovens

Appliances

• Ranges

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Appliances

• Ranges

Appliances

• Improper combustion of burners can be the result of:

– Incorrect fuel

– Incorrect adjustment

– Burner component mis‐alignment

– Blockage of burner passages

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Appliances

• Oven burners

– Standing pilot

– Spark igniter

– Hot surface igniter

• Mechanical vs. Electrical systems

– Standing pilot

– Spark igniter

– Glow igniter

Appliances

Range Component Examination

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Appliances

• Clothes Dryers

Appliances

• Clothes Dryers

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Appliances

• Clothes Dryers

Appliances

• Clothes Dryers

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Appliances

• Clothes Dryers

– Hot surface igniter

Appliances

• Radiant Flame Sensor/Switch

– Bimetallic switch with a ‘window’ that looks into the burner tube

– Normally closed contacts open upon seeing sufficient radiant heat from the glowing igniter or flame

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Appliances


– XXXX

Appliances

• Dryer burner cycle of operation

1. The thermostat calls for heat

2. Power applied to Booster Coil, Holding Coil and Igniter. Valve #1 opens

3. Flame Sensor opens upon seeing glowing igniter

4. Booster Coil and Igniter are de‐energized, Secondary Coil energized. Valve #2 opens

5. Thermostat opens when satisfied, removing power and causing valves to close.

If the flame goes out before the thermostat is satisfied, the Flame Sensor will close, Valve #2 will close and the ignition cycle will re‐start.

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Appliances

• Clothes Dryers

Appliances

• Clothes dryer failure modes


– Improper fuel


– Blocked vent

Control failures

– Leaking gas control valve

Operator error

– Lint!!!

– Flammable/combustible liquids/residue on load fabric

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Appliances

Dryer Component Examination

Appliances

• Furnaces

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Appliances

• Furnaces

– Conventional (Atmospheric)• Open burner tubes

• Simple heat exchanger (low efficiency)

• Exhaust plenum & atmospheric vent

Appliances

• Furnaces

– Mid/High‐efficiency (Power vented)• Open burner tubes or sealed combustion chamber

• More elaborate/efficient heat exchanger

• Exhaust fan

• Plastic vent system

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Appliances


– Typically control pilot and main burner gas

– Typically include a 100% safety shutoff system (e.g., mV or Flame Rod)

– May incorporate ignition system (e.g., spark or hot surface igniter)

Appliances

• Burner Assembly

– Gas flows through a manifold to individual orifices

– Gas mixes with air and is ignited before going into the heat exchanger

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Appliances

• Flame rectification

– An AC voltage is applied between the Flame Rod and grounded metal parts (burner or pilot housing)

– When a flame fills the gap between the rod and grounded metal parts, it acts like a diode and produces a DC signal

– If the rod shorts out, an AC signal is produced

– Requires AC power and sophisticated controls

• Fan/Limit Switch

– Controls when the circulating fan starts/stops

– Acts as a high‐temperature limit switch in the event the furnace overheats

Appliances

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Appliances

• Furnace failure modes


– Improper fuel



Control failures

– Fan/Limit switch failure

– Leaking main/pilot burner valve


Operator error


– Lack of maintenance

– Flammable vapors entering combustion chamber

Appliances

• Furnace examination

– Gas supply

– Gas control valve

– Burner assembly

– Combustion chamber

– Heat exchanger

– Exhaust plenum

– Exhaust vent

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Appliances

Furnace Case Study

Online Appliance Resources

• Appliance411.com

• Appliancepartspros.com

• Repairclinic.com

• Partselect.com

• Inspectapedia.com

• Grayfurnaceman.com

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BONUS!

Portable LP Cylinders, Valves and Regulators

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• Cylinder markings

• DOT‐4BA240 = Built to US DOT specifications

• M4875 = Manufacturer ID No. (Worthington Cylinder‐Westerville)

• Requalification Marking –Specifies requalification within 12 years of manufacture date. Additional requalification dates are stamped on collar.

DOT‐4BA240

Requalification Marking

M4875


• Cylinder markings

• WCW = Manufacturer (Worthington Cylinder‐Westerville)

• TW = Tare Weight (lbs.)

• 07‐97 = Mfg. date

• WC = Water Capacity (lbs.)

• DT = Dip Tube Length (in.)

TW‐17.0 LB 07‐97

UL Listing Mark WC‐47.7

WCW

DT‐4.0

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• Overfilling Prevention Device (OPD)

– Required on 4‐40 lb. propane cylinders since 2002 (or as early as 1998)

– Prevents filling of cylinder more than 80% with liquid

– Some exemptions for horizontal cylinders for lift trucks, etc.


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Hand WheelYou can tell this is a newer ‘Overfill Protection Device’ (OPD) style cylinder valve by the letters OPD on the hand wheel and valve body and the wheel’s triangular shape (the old non‐OPD versions had round hand wheels).

OPD ValveStops flow of gas/liquid into cylinder during filling when liquid level in cylinder pushes the float up.

Relief ValveVents gas from the cylinder in the event of overpressure.

Main Cylinder ValveUsed to let gas flow in/out of the cylinder during filling and use.

Bleed ValveUsed to manually vent the cylinder or check liquid level.

Dip TubeExtends down into cylinder, will vent liquid out of bleed valve if cylinder is overfilled.

Automatic Shutoff Valve This valve must be pushed in by connecting something to the outlet before gas will flow out of the cylinder.

Connection ThreadsExternal for ACME/QCC fittings (CGA‐791) or internal for CGA‐510 fittings.

Liquid propane goes up the dip tube and out the bleed valve hole (when the screw cap is opened) to check liquid level in the cylinder during filling.

Propane gas vents from the headspace of the cylinder through this hole and out the pressure relief valve when the cylinder pressure exceeds the designed relief pressure.

Liquid propane enters through the inlet fitting and flows into the cylinder through the OPD valve during filling. Propane gas from the headspace of the cylinder flows through the holes in the side of the OPD valve and out of the cylinder during use.


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During filling propane enters the top of the OPD valve and flows into the cylinder through the holes on the side of the valve assembly. A small amount of propane flows down between the main OPD valve and the float valve. When the float arm rises it closes the float valve causing pressure to build up between the main OPD valve and the float valve. This causes the main OPD valve to close, stopping flow of propane into the cylinder.

Float Valve

Main OPD Valve



• Pressure Regulator

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• Excess Flow Valve

Appliances

• Oil Burners

– Used on various appliances

– Operate on a range of liquid fuels, including: fuel oils, diesel, kerosene and some bio‐diesel and jet fuels

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Appliances

• Oil Burners

Appliances

• Oil Burners

– Burner components• Fuel pump

• Fan

• Orifice/Nozzle

• Ignition transformer/Electrodes

• CAD cell/Primary control

(relay safety) system

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Appliances

• Oil Burners

– Orifice/Nozzle• Vary in flow (GPH), spray angle and droplet size

Appliances

• Oil Burners

– Ignition system• High‐voltage transformer

• Electrodes

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Appliances

• Oil Burners

– Cad Cell/Primary Control System• Photo‐sensitive cell that changes resistance with light input

• Used to ‘look at’ burner flame to ensure ignition

• Sends signal to control system

CadCell

IgnitionTransformer

Appliances

• Oil burner failure modes



– Incorrect orifice/nozzle


– Incorrect burner/flame adjustment

Control failures

– Control system failure


Operator error


– Lack of maintenance

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Appliances

• Electric Water Heaters

Appliances


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Appliances


Appliances

• Thermostat/TCO

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Appliances

• Thermostat/TCO

Appliances

• Thermostat/TCO

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Appliances

• Failure modes

– Running heaters dry

– Leakage onto live parts

– High resistance connections

Fuel???

Appliances

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Appliances

Appliances

• Failure modes

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Appliances

• Failure modes

Appliances

• High Efficiency Water Heaters

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Appliances

• Tankless/Point‐of‐use Water Heaters

Appliances

• Hybrid Water Heaters

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Summary

• Operation and failure modes of basic gas system components– Pressure regulators

– Gas meters

– Valves

• Operation, failure modes and examination of select gas appliances– Gas water heaters

– Furnaces

– Ranges

– Clothes dryers

– Portable gas systems

– Oil burners

– Electric water heaters

Questions

Jeremy Neagle, P.E.Electrical EngineerATF Fire Research [email protected]‐648‐6215

Documents

GFIA Gas Systems and Appliances - 8 hr - gaiaai.orggaiaai.org/Files/Other/Gas Systems and Appliances.pdf · 7/21/2017 2 Topics Introduction to gas systems and appliances • Gas Systems