Originally published by Fire Engineering
This module focuses on the hidden dangers of a hazardous materials incident and the dynamics that affect a first-due company’s response. The aim of this is to provide the basics for you to expand your training arsenal to your district and your company’s target hazards. This is merely a springboard for suggested training guidelines and materials you can use for your hazmat drills. Scroll down to access simulations.
In this scenario, we will look at a reported vehicle fire on an interstate. First-responding units come upon an over-the-road commercial tanker with fire showing. As the first-due company, it’s incumbent upon everyone operating on the fireground understand the inherent complexity of the incident and the need for specialized resources.
The simulation illustrates arrival conditions. Note that the incident occurs on a three-lane interstate with a shoulder. First-arriving units find a commercial tanker located on the shoulder with the rear of the tank engulfed in flames. There is one occupant (driver) in front of his vehicle who is semi-alert, exhibiting the following symptoms: burning/red eyes, chest pain, lack of responsiveness, agitation, and pain in the mouth/throat.
One of the immediate challenges this scenario presents is size-up. Due to the location of the incident and constant flow of vehicle traffic, size-up will be limited to the first-arriving units. There are three factors that are important to prioritize during the first minutes after arriving.
- Determine safe work zone for all first responders
- Identify the downwind and upwind areas
- Are the occupants visible and/or in immediate danger?
- Verify and determine level of entrapment (if applicable)
- Type of Vehicle
- Type of road trailer?
- Are markings, labels, or placards visible?
- Type of Vehicle
- What resources are responding?
- Are additional resources needed?
- Determine the best access for rescuers and positioning of incoming apparatus
The answer to these questions will determine how the incident progresses over the duration of the call. A thorough knowledge of your first due will expedite the speed in which these decisions will be made. On the surface, this incident presents only two challenges: the immediate fire hazard present and operating conditions on the interstate, both of which are visible life safety hazards. However, those familiar with such incidents will be keen to point out the inherent complexity and dangers that face all first responders. But how can we teach those affecting fire suppression operations the dangers they may face in the near future? More importantly, we must give them the tools and knowledge they need to understand their limitations and the associated risks they face when they go downrange.
With no clear markings or placards visible, it becomes imperative to ascertain what this over-the-road tanker is transporting. What effect does fire have on said contents? What effect does water has on the substance? Thus, the next benchmark becomes identification.
- Are the occupants accounted for?
- Determine level of entrapment (if applicable)
- Is rescue required or possible?
- Triage and patient packaging
- Narrow down possible content category
- Create list of known factors/brief for subject matter expert
- What additional resources are needed?
- Fire Suppression
- What effect does fire suppression operations have on the contents?
Specific ‘Hidden dangers’
As many know, the answer to these questions are often split-second decisions, which highlights the need to answer these questions in training prior to the event occurring. This is the basis for what we do and responsibility we have to those we serve. However, it is still unclear the forces at work unseen to the naked eye. Two possible factors at work are vapor density and specific gravity. One might think that these factors are independent, but that was not the case in this scenario. A third factor to consider is the impact of chemical reactivity to fire suppression operations.
Factor #1. Vapor Density
Vapor density is the relative weight of a gas or vapor as compared to air, with air being given a numerical value of one (1). For example, If the vapor density is 0.79 thus less than one (1), then that vapor will rise in normal atmosphere. Conversely, if a gas has a vapor density greater than one (1)—for example, if the vapor density is 1.79—that vapor will sink and concentrate in normal atmosphere. This is important to note because most hazmat incidents are not easily identifiable through sight or smell and there are only 14 gases that have vapor densities less than 1.
Factor #2. Specific Gravity
A second hidden danger is the consequence of the substance’s specific gravity. Specific gravity is the ratio of a liquid’s density as compared to water, with water being given a numerical value of one (1). Thus, if the specific gravity is less than one (1)—for example, 0.79—then that liquid will float in water. Conversely, if a liquid has a specific gravity greater than one (1), that liquid will sink in water.
The misconception is that these dangers only apply independently of one another. In fact, when impinged by fire or when the container is damaged and exposed to outside elements, the reaction can compound their effects. In this scenario, the trailer contains sodium hypochlorite (>15% concentration in liquid form) which is stable as a liquid when contained under normal operating conditions. However, fire is not a normal operating condition. In the quantities present during the incident, the chemical is an oxidizer. In addition, when heated, the liquid decomposes and has the potential to produce three hazardous gases: hypochlorous acid, chlorine, and hydrochloric acid. All of these have a vapor density greater than one (1) and all of these create a low-lying immediately dangerous to life and health (IDLH) atmosphere. This means that by the time the first unit arrives, an IDLH atmosphere is forming around the base of the vehicle and is increasing in size and magnitude with each passing minute.
The easiest and most efficient way to determine this information is to make contact with the driver. With single payload tankers such as this, often the driver will know what they are transporting and have access to their bill of lading, which has actionable information that will expediate mitigation and fire suppression operations. That said, there are many factors that could prevent this exchange from occurring.
Scope is a key factor on any incident and crews must recognize early that the incident has the potential to be beyond their capabilities. If you are unable to ascertain the contents, you must begin to narrow down what could be contributing to this incident. This type of over-the-road tanker is categorized as a DOT MC412 trailer. Practically, this provides responders with the contents usually contain corrosive liquids and it has a maximum operating pressure of 15 PSI, which suggests that the contents have a potential to create an IDLH atmosphere pending a leak, spill, or failure due to fire impingement or damage. Additionally, the operating pressure is low which suggests a boiling-liquid, expanding-vapor explosion (BLEVE) is unlikely under normal operating conditions. However, without access to specific contents information or even a placard, this incident is rapidly increasing in scope.
With an uncertain incident, any change or deterioration in conditions can negatively affect the uninhibited chemical reaction that is occurring. More importantly, the actions taken by first responders have the potential to dramatically increase the hazards placed on those operating in and around the fireground. The accompanying image is a picture of the underbody of the trailer. Above the frame rails, there is a constant leak occurring which is creating white puddles in and around the wheels of the trailer. In addition, this area is being impinged by fire. This along with the patient’s symptoms and unknown contents should dictate the need for specialty resources such as a hazardous materials response.
Factor #3: Chemical Reactivity to Fire Suppression Operations
Another challenge this incident presents is the chemical reactivity to fire suppression operations. In this scenario, liquid sodium hypochlorite is actively leaking onto the interstate and surrounding green space. Although the chemical is nonflammable, when exposed to heat, the chemical releases chlorine gas and hydrochloric acid. Moreover, the chemical is decomposed by heat and light, causing a rapid increase in pressure. As indicated previously, in the quantities present it is also an oxidizer which increases combustion. An advantage for the responders in this scenario was that this chemical is water soluble. In other words, it can be diluted with copious amounts of water. Hydraulic ventilation using a 60+° fog pattern will entrain air and help disperse the low-lying toxic vapors being produced by the decomposition of the liquid. It is important to note that apart from chlorine’s toxic properties and limited visual detection, chlorine vapors deteriorate structural turnout gear; this can be seen in the rapid discoloration of the outer shell.
In the end, the first-arriving crew established an initial safe zone of 800 meters; designated hot, warm, cold zones; and requested a hazmat officer response. Ultimately, using a defensive appliance to extinguish the fire, cool the container, and hydraulically ventilate the low-lying vapors while committing minimal personnel to the hot zone until hazmat resources arrived. Once on scene, hazmat personnel conducted offensive operations to mitigate the subsequent spill but were unable to mitigate the leak due to the damage sustained due to the fire.
While awaiting the chemical transfer, an excavator was requested and used to dig a containment ditch to collect the product in the event there was a total failure of the container. Once the remaining chemical was pumped out of the original tanker into another, the scene was turned over to a third party for cleanup. Thanks in large part to the training and experience of the responders, this incident ended in success. But what if one of those factors had been different? What if instead of a vehicle fire it came in as a vehicle accident with entrapment under similar conditions? What if the chemical had been different and unstable or violently reactive to water? Thankfully, these are all questions that did not have to be answered during the incident. A successful mitigation of your future road incident may very well hinge on properly considering these factors in your response.