On a hot summer afternoon, your bulk plant is in the process of off-loading 33,000 gallons of propane from a railroad tank car.
As the unloading process continues, a thunderstorm begins to develop and move in from the southeast.
The decision is made to stop off-loading the rail car until the storm passes.
Before the pump is shut down, the rail car unloading rack is hit with a direct lightning strike and a fire breaks out.
A technician at the pump house sees a small fire at the dome of the tank car.
He immediately hits the Emergency Shutoff Valve (ESV) switch at the pump house and a controlled and safe shut down of the plant begins.
The ESV automatically shuts down the propane liquid transfer pump, closes valves in the transfer system, and activates the plant’s emergency alarm to alert other employees of the emergency.
Within seconds, the system is completely isolated.
After activating the plant ESV, the operator calls the local fire department and returns to the loading rack where he activates a fixed fire monitor tied into the plant’s domestic water system.
A large fire stream from the 500 gallon per minute (gpm) monitor is directed onto the rail car’s tank shell near the dome.
By the time the fire department arrives the fire has already gone out.
If you have good engineering controls, trained personnel, and a well-thought out Emergency Response Plan it could happen this way. Fortunately, most emergencies in industrial facilities never develop into major events because the scenario was anticipated and planned for before the event actually occurred. As an owner or operator, you understand the hazards of propane. But have you looked at possible emergency response scenarios within your plant? What are the probability and consequences of each scenario? This process is a critical benchmark in developing a facility Emergency Response Plan.
Sometimes known as "Scenario-Based Emergency Planning," this process assists you in:
The terms HAZARD and RISK are often used interchangeably but from an emergency planning perspective, they actually have very different meanings and represent two different activities in the planning process.
HAZARDS are materials, processes, or locations within the plant that may pose some danger or peril. In emergency response operations, hazards generally refer to the physical and chemical properties of a material under certain conditions. For example, propane has very specific characteristics such as boiling point, vapor density, expansion ratio, and flammable limits which determine how it and its container will behave under both normal and emergency conditions. The hazardous characteristics of propane remain constant. Propane will always be propane regardless of the size or type of storage container, location etc.
RISK is the probability that something will go wrong. Unlike hazards, which are constant and fairly easy to identify, risks are variable and may change. Within the fields of Process Safety Management and Safety Engineering, there are many risk evaluation tools used to help determine the probability that an event may occur and the consequences of that event. However, from an emergency planning perspective, the risk assessment process can be simplified by focusing on scenarios that represent the range of credible events that could happen.
Experienced emergency planners develop Emergency Response Plans based on scenarios that are "credible". In simple terms, a Credible Scenario is believable and falls within the range of accepted probability. It may be based upon either actual experiences within the facility or historical experience or events within the gas industry at-large.
On one end of the spectrum are emergencies that have a very low probability of ever occurring, but for which the consequences would be severe. An example of this scenario would be a fully loaded passenger aircraft crashing into your bulk plant with all of the storage tanks filled to capacity. This scenario is not very likely, but it could happen. However, if you developed your Emergency Response Plan around this scenario your plan will not be very realistic in addressing the more likely and probable events.
At the other end of the spectrum are scenarios that have a very high probability of occurring, but the consequences will be minimal. An example of this type of scenario might be a trash dumpster on fire in the plant’s parking lot. An Emergency Response Plan built around this scenario would also be deficient in addressing emergencies that may test your capabilities and operations.
If we listed all of the possible emergency scenarios and placed them on a scale with Low Probability/High Consequence events on one end and High Probability/Low Consequence events on the other end, the "credible" emergencies would be somewhere in the middle. Although selecting credible scenarios can be somewhat subjective, there are some practical guidelines that can be used to determine what should be addressed in the Emergency Response Plan. These include:
Identifying the real hazards within your facility is a key step in determining the types of credible emergencies that could occur. These should include both physical and chemical hazards, including fires, releases, and confined spaces.
Fire and leak scenarios involving propane storage and loading/off-loading systems should be practical and take into consideration how the system is designed to function during an emergency. Although large quantities of liquid propane may be found in storage vessels, most emergency response events involve the transfer and handling of product.
Depending upon local requirements, some facilities may have a range of engineered fire detection, fire suppression, and emergency shutdown systems in-place. In addition, the fire flow requirements and flow capabilities of either the plant or local water system should be assessed.
Exposures can include people, property, environmental or systems that could be impacted by an emergency in your plant. Systems can range from transportation systems (e.g., railroad, highway and air corridors) to impacts upon electrical and utility grids. For example, if you have a propane leak and there are special occupancies downwind (e.g., school, nursing home, etc.), what are the procedures for notifying these occupancies? If there is a vapor release involving your facility, will it potential impact the highway or railroad corridor that adjoins your facility?
Neighboring facilities could also pose a threat to your facility if they have an emergency. For example, if the facility next door stores or uses certain liquefied gases such as chlorine or anhydrous ammonia, how will it affect your plant? Are there procedures in-place for notification of your facility?
This is a top-perspective view of the incident area. Its purpose is only to get the general idea of the incident and surroundings.
In this section, we present an animated version of the incident.