Natural Gas and Propane Explosions Explored and Explained

In the quiet of a typical evening, a sudden eruption shatters the calm—a house explodes into flames, a devastating and mysterious scene. What could have sparked such a violent reaction? The answer often lies in the utilities that warm our homes and cook our meals: natural gas and propane. Though largely invisible and odourless, these fuels play pivotal roles in our daily lives, yet they carry inherent risks of explosions when not adequately managed.

This article discusses the mechanics and dangers of natural gas and propane explosions. By understanding the distribution systems, the properties of the gases, and the safety measures in place, we can appreciate the delicate balance between utilizing these resources and ensuring safety in our communities.

Natural Gas Distribution System Overview

While similar to the propane industry, the natural gas distribution system possesses unique characteristics. It begins at a gas well or a collection area, typically an oil and gas setting, where natural gas is extracted.

After extraction, the gas is transported to a gas treatment station and processed. Oil and water separate during this stage, and undesirable gases are vented or flared off.

The next phase involves a gas processing plant where products and non-hydrocarbon gases are removed. The aim is to refine the gas to a high purity level for end-user consumption. This gas then passes through a compressor station, which helps maintain the flow and pressure within the pipelines.

The treated gas is stored in gas storage wells or directed into the pipeline system for delivery. Notable storage includes the Dawn facility in Ontario, an underground cavern where gas is stored until needed. Some regions depend entirely on pipeline systems without local storage facilities, operating strictly based on demand.

This structured process ensures the delivery of clean and efficient natural gas through a sophisticated distribution system catering to various consumer needs nationwide.

Gas Transport

In transportation, natural gas is moved through transmission lines at pressures ranging from 900 to 1500 pounds per square inch gauge. Maintaining high pressure is crucial for adequate transportation through the pipeline. It is important to note that the gas is not odorized at this stage since it is still within the transmission lines. Odorization of the gas occurs later in the process, closer to the point of distribution to end users.

Gas Distribution

Once the gas reaches a distributor’s gate station, the pressure is significantly reduced using regulators to approximately 60 pounds per square inch, preparing it for entry into the distribution pipeline. At this point, the gas is odorized with mercaptan, which emits an odour similar to rotten eggs. This addition is crucial as natural gas in its original state is odourless, and adding mercaptan ensures leaks can be detected by smell.

The odorization process is meticulously controlled at the gate station, with specific amounts of mercaptan added to achieve the desired level of odorization. This ensures safety and detectability by individuals. Distributors such as AltaGas, Enbridge Gas, or local entities like Go Gas in Manitoba handle this process, each adhering to standards that govern the introduction of mercaptan into the gas.

Following odorization, the gas is distributed through trial and residential consumers. The distribution system through pipelines consists of underground pipes that extend throughout municipalities, delivering gas to individual properties. The gas pressure is further regulated down to levels suitable for specific uses: industrial sites might receive gas at five or ten pounds per square inch, whereas residential areas typically receive it at four ounces or seven inches of water column pressure.

Residential Meter Setup

The residential meter setup includes a regulator on the left-hand side and hose piping on the right side, with a gas shutoff at the bottom. The gas is regulated through a service regulator outside the home, passing through a meter at approximately four ounces or seven inches of water column pressure.

Mechanical Room Setup

In residential settings, the gas is piped to the mechanical or furnace room and utilized in various appliances for heating and cooking. Typical installations include a residential furnace, water heater, stoves, barbecues, gas dryers, and gas fireplaces. The gas is distributed into the home through smaller lines to support these applications.

Natural Gas and Propane Properties

Natural gas has a five percent lower explosive limit, corresponding to about 45,000 parts per million, and an upper explosive limit of 15 percent, or approximately 100,000 parts per million. This indicates that natural gas will ignite or explode within this gas concentration range to air. Propane has similar properties but with a lower explosive limit of 2.15 percent and an upper limit of 9.6 percent, defining the potential ignition or explosion range.

Vapor Density and Ignition Temperatures

Natural gas’s vapour density is 0.6, meaning it is lighter than air and will rise. In contrast, propane’s vapour density is 1.5, causing it to settle and linger near the ground. Natural gas’s ignition temperatures range from 900 to 1170 degrees Fahrenheit, while propane ignites between 920 and 1120 degrees Fahrenheit. A spark in the presence of heat energy can ignite both gases.

Heating Values

Natural gas offers a BTU (British Thermal Unit) value of about 1,000 per cubic foot, whereas propane provides significantly more energy, approximately 24.88 BTU per cubic foot. Despite propane’s higher energy output, it is generally more costly and undergoes a more complex preparation process for consumer use.

Odorant Characteristics and Explosive Force

Both natural gas and propane are odourless in their natural states and are odorized for safety. Mercaptan, which smells like rotten eggs, is added to make gas detectable at 20 percent of the lower explosive limit. This process is carefully controlled at gate stations, ensuring precise odorization to prevent leaks and ensure safety.

Explosive Force Dynamics

The explosive force of gas depends on the gas concentration in the air. Most explosions typically occur at approximately twice the lower explosive limit (LEL), where there is sufficient air for complete combustion, known as the stoichiometric concentration. This level is around 10 percent for natural gas, and for propane, it is about 4 percent, marking the conditions for the most intense and complete combustion.

Fire

This is an example of a house that exploded. The situation is tricky because if there is a higher concentration of gas to air mixture, there can sometimes be more flame after the explosion due to unburned gas catching fire. Certain appliances within the home can also cause a fire more than after the explosion. It is difficult to determine the exact concentration of gas-to-air mixture, but typically, if there is more flame after, it is usually higher on the spectrum.

Some factors that affect the detection of the odorant include aging, which can reduce the sense of smell, and competing odours within the home. For example, strong scents like an odorant can overpower other smells, challenging detecting gas odours. Additionally, some people cannot detect odorants at all, and it’s important to note that the sense of smell shuts down when you are sleeping. There have been instances where people have said they were in bed during an explosion and didn’t smell the gas due to this.

New steel piping or fresh paints can cause an odorant to fade, though investigations have not directly indicated this. However, there have been situations where the soil has scrubbed out the odorant, and people have not been able to detect it with their noses, particularly in underground leaks.

Gas Fire Explosion Investigation

Discussing gas fire explosion investigations, this is a typical house explosion followed by a fire believed to be in Ontario. Personal safety is crucial, and the first thing checked is whether the gas has been shut off or diverted, who did it, and when. It’s vital to ensure the gas is completely shut off. Checking if the gas company performed barbells to check for underground leaks is also crucial.

The scene is assessed for recent construction or underground excavations, which might have damaged gas lines. The presence and depth of frost are also considered, as they might trap gas underground. It’s essential to determine if the utility or regulatory authority was present at the incident, as they usually have the expertise to shut off the gas. Although they tend to remove their meter and regulator from the scene, it is preferable to photograph these in place for investigation purposes.

Additionally, it’s necessary to know if any gas or oil wells in the area could leak. Any gas odour at the scene is noted to ensure the gas has been shut off. This thorough approach is essential for ensuring safety and conducting a detailed investigation of gas fire explosions.

Bar Rolling Tests

Bar rolling tests are conducted to rule out an underground leak from any of the existing gas lines. The gas company or the distribution company usually does the test. It consists of pounding a metal rod off the side of the located gas line to a depth of between 12 inches and 20 inches. A natural gas detector probe is placed in the hole to detect natural gas in the ground. If readings are found, it may indicate an underground leak. This test can also be performed on propane lines; after the first stage regulator in a propane setup, which usually goes underground to the house, bar rolling can be conducted on the underground line going from the second stage regulator to the first stage regulator to check for leaks.

Scene Investigation

It’s essential to understand the conditions before the gas fire explosion. Determining if any construction was done recently, if there was frost on the ground, and if any gas or appliance work was carried out lately is critical. Inquiries should include whether any gas valves were turned on or off, if someone was trying to light an appliance where the pilot light might have gone out, or if the gas service was disconnected or reconnected. It’s also important to know if anyone smelled anything unusual before the explosion to establish a timeline and identify potential causes.

Meter Setup

Understanding the meter’s setup is essential. Typically, the setup includes a regulator that reduces the pressure from 60 pounds to four ounces or seven inches of water column. This is indicated by the meter’s shut-off position, which is aligned with the pipe in the ‘on’ position and perpendicular when ‘off.’

These detailed investigations and tests are crucial for pinpointing the causes of gas explosions and ensuring the effective implementation of future safety measures.

Freezing Rain

This example discusses a meter exposed to freezing rain, which poses significant risks. The vent on the regulator can freeze in the open position, allowing gas to continue flowing through the system even when no demand is downstream. This scenario leads to a dangerous buildup of pressure in the line, which can result in the bursting of valves downstream. Typically, these valves are only rated for two pounds of pressure, and the buildup can occur quickly if the regulator is frozen open.

In Ontario, gas explosions have been caused by crossbar excavation, a severe issue where a gas main is installed through a new subdivision or during gas line renewal. Sometimes, the installation process, Directional Boring, inadvertently penetrates sewer lines. Over time, these sewer lines may become blocked. Directional Boring is a technique for installing various infrastructures, such as water lines, sewer lines, gas lines, airline product pipelines, and environmental remediation casings.

The process involves boring a pilot hole and successively larger reamed-out holes while removing the dirt and drilling mud. Once the borehole is sufficiently large, the pipeline is pulled through, and the installation process continues with standard trenching methods. This situation highlights the critical need for careful monitoring and control during gas line installations to prevent dangerous conditions such as gas leaks and explosions.

Cross Bores

Cross bores occur when underground natural gas pipes are incorrectly installed through sewer or septic pipes. Cross bores are not an immediate safety risk if left undisturbed and can remain unnoticed for years without causing issues. However, they become hazardous when equipment that unclogs sewer and septic pipes, such as cutting tools, accidentally penetrates a natural gas pipe. This is particularly problematic during line staking processes.

The danger escalates significantly if the cutting tool breaches a main gas line, which could be under 50 to 60 pounds of pressure. When this happens, and a plumber uses a snake to clear a blockage, all the pressurized gas can rapidly flow into the house through the newly created opening, creating a severe safety risk. This highlights the critical importance of proper installation and maintenance practices for underground utilities to prevent dangerous incidents involving cross bores.

Open Gas Lines

Open gas lines can sometimes be found when people move out or in, and while this is not typically seen in new houses, it does occur. Determining whether an open gas line results from an accident or intentional action is crucial. In most cases, it is accidental. People often leave these lines open by disconnecting appliances like stoves or dryers and forgetting to cap or plug the line. Additionally, the absence of a shut-off valve on the line can exacerbate the problem, as the gas might flow freely through the pipe.

In the event of a gas explosion, finding an open gas line in the debris is a significant clue. Investigators would need to ask various questions to understand the situation better. Questions might include whether the occupants had recently moved in or if they had replaced a gas dryer with an electric one but forgot to cap the line. Answers to these questions can guide the direction of the investigation, helping to uncover the underlying causes of the incident. This understanding is crucial for preventing future accidents and ensuring the safety of residents.

Gas Application

For gas appliances, connectors are commonly used. These for gas appliances, such as dryer connectors, are typically yellow, although they can also be found in plain stainless steel, which is just metal without any coating. These connectors are crucial in safely delivering gas to appliances, ensuring a secure and leak-resistant connection.

Propane Considerations

Special considerations for propane systems include determining if a service call was involved. This could indicate that the propane company recently visited to fill the tank or modify the system. When the tank is empty, the gas company is responsible for checking the entire system for leaks, which includes appliances, lines, and valves. Additionally, they are tasked with relighting pilots for the homeowner. If there has been an outage, the gas appliances inside must be relit once propane is reintroduced into the system.

Sunrise Propane Explosion

The Sunrise Propane explosion occurred in the late 2000s, around 2008 or 2009. This incident involved a high explosion resulting from a tank-to-tank transfer at a Sunrise Propane facility. The explosion was captured in a photograph taken from a distance, illustrating the scale and intensity of the event. Such explosions underscore the potential dangers of handling and transferring propane, particularly in large quantities.

Propane Explosion Myths

Myths surrounding propane explosions include believing that propane explosions blow walls out from the bottom while natural gas explosions blow out at the top. Additionally, there is a common misconception that propane explosions are more destructive than natural gas explosions due to higher pressure and faster flame fronts. However, in practice, the damage from propane and natural gas explosions often appears similar, making it difficult to distinguish between them based solely on the aftermath.

It is important to remember that most gas leaks, which lead to explosions, are caused by actions or inactions that deviate from safety procedures. Investigating these incidents focuses on determining why and how the gas leaked and what ignited it. An explosion signifies that understanding the origin of the ignition is a priority.

Key facts to consider about gas safety include:

• Natural gas is lighter than air and will always rise.
• Most gas mains are installed underground at a minimum depth of 12 inches, though typically only a little deeper than 24 inches.
• Odorants are added to the gas at the gate station to aid in leak detection.
• The explosive range for gas is generally between four and fifteen percent.
• Gas installations are expected to be performed by certified installers and usually involve a permit system or some form of quality control.
• Gas companies or inspectors conduct a small sample of installation inspections, but they must inspect all new installations.
• When gas meters are activated, they must comply with regulations, and the gas company must ensure that all connected appliances have been inspected before the gas is turned on.
• Gas companies also conduct periodic surveys of underground line leaks using sensitive equipment, typically at a three-year interval.
• Questions often arise during investigations about the location of the gas meter and regulator. Typically, the gas company retains these components throughout the entire investigation. All piping after the meter is considered the property of the customer or the insured, and it is usually kept with the investigator acting on behalf of the insurance company.

Propane Distribution Systems

Propane is heavier than air, which causes it to settle at the lowest level. The fuel is stored in various containers, tanks, and cylinders. Despite some systems existing for propane distribution, they are relatively rare, with most fuel being sourced from tanks or cylinders.

Cylinders require inspection and recertification every decade, and an odorant is added to the fuel for safety purposes. Propane’s explosive range lies between two and nine percent. Gas installations must be inspected by certified installers, who are usually required to obtain a permit. Inspections may be revisited, though this is not consistently enforced.

Propane companies must inspect all new installations when they supply propane to a new customer to ensure code compliance. Although not always mandated by regional regulations, most companies perform these inspections as part of their due diligence.

Unlike natural gas setups, the customers typically own propane system regulators. Because propane is heavier than air, it will seek the lowest possible level where it can accumulate, potentially entering drains, gutters, and sewers.

Conclusion

Understanding the roles of natural gas and propane in our daily lives underscores the importance of stringent safety measures. This exploration of their properties and distribution systems highlights the balance between using these energy resources and ensuring public safety. Explosions, though rare, remind us of the potential dangers associated with improper handling.

This article emphasizes the need for robust safety protocols, vigilant maintenance, and ongoing education to prevent accidents. As consumers, staying informed about our home gas systems is crucial. Industry professionals and regulatory bodies must enforce and continuously refine safety regulations. We can safeguard our communities against natural gas and propane dangers through awareness and diligence.