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7 Knowledge Objectives (1 of 2) • Explain the impact of fuel gases on fire and Fuel Gas explosion investigations. Systems • Discuss the characteristics of fuel gases. • Identify common fuel gas system components. • Discuss common piping for fuel gas systems in buildings.
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Knowledge Objectives (2 of 2) Skills Objectives • Discuss common appliance and equipment • Conduct a fire and explosion investigation for requirements. fuel gas systems. • Identify fuel gas utilization equipment. • Describe how to investigate fuel gas systems.
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Introduction Fuel Gas Systems (1 of 6) • During every investigation, presence and • Used to: condition of fuel gas systems must be: – Control indoor climate – Examined – Heat water – Documented – Cook • Fires and explosions often result from failures – Provide energy for manufacturing within these systems.
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Fuel Gas Systems (2 of 6) Fuel Gas Systems (3 of 6) • Most common: natural gas and commercial • Natural gas explosion scene. propane • Can act as: – Initial fuel source (escaped or “fugitive” gas) – Initial ignition source – Both fuel and ignition source
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Fuel Gas Systems (4 of 6) Fuel Gas Systems (5 of 6) • Fuel sources • Ignition sources – Fuel involvement usually results from – Pilot lights and open flames from appliances compromised fuel delivery or containment served by fugitive gases systems. – Static arcs from appliances – Fuel that is escaped may be called “fugitive gas.” – Electrical arcs – Arcs from switches or contacts in appliances – Other electrical equipment
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Fuel Gas Systems (6 of 6) Characteristics of Fuel Gases (1 of 4) • Both fuel and ignition source – Fuel gases can serve as both the first fuel and the fuel for the fire. – Fugitive fuel provides fuel for the fire to grow. • Additional fire spread – Fire can spread because of fugitive fuel gas. – Natural gas and propane are common residential fuels.
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Characteristics of Fuel Gases (2 of 4) Characteristics of Fuel Gases (3 of 4) • Natural gas • Commercial propane – Hydrocarbon gas composed primarily of methane – Recovered during the process of refining – Often recovered from underground pockets during petroleum drilling for crude petroleum – 95% propane and propylene and 5% other gases – Lighter than air – Heavier than air – Flammable range 3.9–15% – Flammable range 2.15–9.6% – Ignition temperature of 900°F to 1170°F (482°C to – Ignition temperature of 920°F to 1120°F (493°C to 632°C) 604°C).
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Characteristics of Fuel Gases (4 of 4) Odorization • Other fuel gases • By law, odor is added to LP‐gas and – Commercial butane commercial natural gas. – Propane HD5 – Butyl mercaptan most often used in natural gas – Coke oven gas – Ethyl mercaptan or thiophane in LP‐gas – Hydrogen • Supply company adds it as a safety feature – Acetylene • Can often be smelled during fire investigation
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Gas Systems Natural Gas Systems • Transport fuel gas directly into consumers’ • Transmitted (in this order) through: buildings and appliances – Transmission pipeline • Natural gas is supplied from central location – Main pipelines (mains) – Via underground supply service lines – Service mains or service laterals • LP‐gas is contained in bulk supply, often at consumer’s location.
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LP‐Gas Systems (1 of 5) LP‐Gas Systems (2 of 5) • Storage supply is often located at consumer’s • Tanks are larger than cylinders. site in tanks or cylinders – Cargo tanks are mounted on a chassis and used to • Alternatively, the gas may be in in bulk storage transport LP‐gas. locations offsite and piped underground, – Portable tanks transport LP‐gas, but are not on a similar to natural gas systems. chassis.
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LP‐Gas Systems (3 of 5) LP‐Gas Systems (4 of 5) • Cylinders are upright and tend to be • Container appurtenances: smaller than tanks. – Pressure relief devices – Most frequently used in rural homes – Connections for flow control and businesses, mobile homes, – Liquid level gauging devices recreational vehicles, and for outdoor – Pressure gauges barbeques and motor fuel – Pressure regulators – Vaporizers
7 7 Common Fuel Gas System LP‐Gas Systems (5 of 5) Components (1 of 5) • A vaporizer is used when there is a demand • Pressure regulation (reduction) for large quantities or propane; it converts – e.g., gas meter liquid propane to gas. • Service piping systems – Delivers gas from the main lines to the user • Valves • Gas burners/pilot lights
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7 7 Common Fuel Gas System Common Fuel Gas System Components (2 of 5) Components (3 of 5) • A large natural gas meter. • A 20‐inch gas main pipeline.
7 7 Common Fuel Gas System Common Fuel Gas System Components (4 of 5) Components (5 of 5) • Furnace burners and gas control valve. • Water heater pilot line and gas control valve.
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Common Piping in Buildings (1 of 2) Common Piping in Buildings (2 of 2) • Maintain evidentiary value of piping and its • The main shutoff valve components controls the flow of gas – Joints and fittings throughout the entire – Piping installation building. – Main shutoff valves • Prohibited locations per NFPA 54 and other codes – Such as air ducts, chimneys, elevator shafts • Electrical bonding and grounding
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7 7 Common Appliance and Equipment Common Appliance and Equipment Requirements (1 of 2) Requirements (2 of 2) • An appliance is compatible with only a certain • Venting and air supply type of gas; gases are not interchangeable. – Exhaust venting prevents buildup of combustion • Appliance installation products. – May need additional regulator – Fresh air from building exterior often necessary – Location where there is easy access and shutdown • Appliance controls – Sufficient clearance between appliance and – For temperature, ignition, and shutoff combustibles – Gas appliance pressure regulators – Gas flow control accessories
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Fuel Gas Utilization Equipment Investigating Fuel Gas Systems • Investigator should be familiar with design • Should be done in systematic, thorough and operation of: manner – Water heaters • Determine whether, and to what extent, – Furnaces system failed – Clothes dryers • Interviews should touch on fuel gas system. – Ranges
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Compliance with Codes and Standards Leakage Causes (1 of 2) • Investigator should determine that codes and • At pipe junctions standards were followed in: – Inadequate threading, improper join, improper – Design use of joint compound – Manufacture • Unlit pilot lights or burners – Construction – Sensing system malfunctions or auto‐shutoff valve – Installation does not operate and gas continues to flow • Additional expertise or resources may be • Uncapped pipes and outlets needed.
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Leakage Causes (2 of 2) Pressure Testing • Malfunctioning appliances and controls • Pressurize the system to isolate damaged – e.g., dirt or debris causes valves to leak sections of piping. • Gas pressure regulators • Gas meters can also be tested. – Failure within internal diaphragm or of seals – If it is safe to reintroduce gas into system – Plugged vents – The meter detects gas escaping from the system. • Corrosion • Physical damage to system
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Locating Leaks (1 of 2) Locating Leaks (2 of 2) • Tests can locate leaks in fuel gas piping • Soap bubble solution test. – Soap bubble test – Use of gas detector survey (“sniffers”)
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Testing Flow Rates and Pressures Underground Migration of Fuel Gases • Should be tested if gas system is suspected to • Gases can travel great distances underground, be involved in fire ignition through: • Can be done in field or at laboratory – Sewer lines • Conducted only by trained, knowledgeable – Electrical and telephone conduits personnel – Drain tiles • Potential ignition sources should be removed • Passing through soil can “scrub” the odorant during testing. out of the gas.
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Summary (1 of 4) Summary (2 of 4) • Fuel gas systems will likely be either natural • Both types of fuel gases will supply fuel to gas or LP‐gas. various appliances that may heat water and • Natural gas systems are generally supplied via the environment and be used for cooking or underground main lines, whereas LP‐gas is various other services. supplied by a consumer tank on the premises.
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Summary (3 of 4) Summary (4 of 4) • Fuel gas systems are often damaged as a • When fuel gases escape underground, they result of other activities occurring in the can be deodorized as a result of the gas structure, allowing fuel gas to escape from the migrating through the ground. system. • Fuel gas system tests should be conducted by trained laboratory technicians.
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