Three-Point Hazmat Size-Up

SCENARIO 1. AN ENGINE IS dispatched to a basement fire in a two-story, balloon-frame house. How is this fire likely to progress? How is this determined? In this case, the fire officer understands the environment the building is in, the likely occupancy including the associated life safety considerations, the building, and the fire’s behavior. Based on this information, the officer develops and implements an incident action plan (IAP).

Scenario 2. An engine is dispatched to a leaking box trailer parked at the local interstate truck stop. A white-over-black placard with the number 1789 is displayed on the side of the truck, and a leak of 60 drops per minute is observed in the area of the rear doors. How is this incident likely to progress? How is this determined?

In any incident, the initial actions taken ultimately set the stage for the successful resolution of the problem. For common incidents such as motor vehicle collisions and structure fires, most fire department personnel are familiar with the appropriate incident size-up, determining the need for additional resources, and IAP. Since hazardous materials incidents are not as common, properly recognizing and assessing the situation are often more problematic.

Recognizing the problem is the key to responder safety. Responders cannot depend on the presence of a hazmat placard, since most materials are not required to be placarded unless more than 1,000 pounds are present. Other clues to the presence of a hazmat are the occupancy, the container (including size, shape, labels, markings, and documentation), and the material’s effects on people and things. Based on recognition of the problem and the observations obtained on the initial approach, responders can assign initial exclusion zones.

The resources available for hazmat response vary by jurisdiction. In some cases, a hazmat or a decontamination unit may be available, but it may take time for it to arrive. In the interim, the officer must perform the initial size-up and develop an IAP.

One approach to the size-up of a hazmat incident involves performing a three-point incident assessment-environment, containers, and materials involved. Other information and additional details can be considered in a hierarchy under each of those major topics, which leads to a tree-shaped structure for information management. Since the officer may eventually need to use data from technical experts, this builds a framework that enables the officer to see the overall picture and have a manageable span of control over the data, in the same way that the incident command system allows for the management of and accountability for a large number of people.

As the data are collected, some key questions can be answered: What have I got? Where is it? Where is it going? What can I do? What resources do I need? This is an ongoing process, and the answers to these and other questions may be refined as the incident progresses.

Using a tree or network for information management also works for other types of incidents such as structure fires and rescues. The key is to use the system to organize the data and clarify things. Although it can be expanded as needed, depending on the nature of the incident, it is a tool to distill things down to the essentials. A hazmat version of this system for information management is shown in Figure 1.



The environment includes the people, places, and things present at the incident. It includes the larger-scale view of things and is, consequently, the first thing you see on approach. Quickly identifying the important items in the incident area is critical, because it addresses the incident priorities of life safety, incident stabilization, and property conservation. In part, the environmental elements may be considered analogous to identifying exposures at a fire scene at which the officer is trying to determine “Who or what do I have to protect?” Some considerations include population, protection, occupancy, geography, accessibility, material confinement, and the length of time the incident has been underway. Scene security addresses additional scene safety and control issues, especially those at a crime scene.

Hazmat incidents are like any other incident in that life safety is the primary consideration. The location and number of people, including emergency services personnel, along with their actual or potential exposure to the material, are of primary importance. Since hazmat incidents are ideally approached from upwind and uphill, one very important safety consideration in evaluating the environment is the weather in the immediate area, particularly the local wind direction and speed. Local features (e.g., waterways, hills, buildings) often influence winds, so the weather data from the airport or other weather station relayed by the dispatcher are not always correct for the particular location. Structures and vehicles may provide significant protection for people and may have facilities such as an HVAC system, which should be controlled to keep the material away from the occupants. In addition to the wind, other weather factors, such as heat and humidity, can greatly affect the behavior of a hazardous material. For example, anhydrous ammonia typically moves upward, but a cloud can interact with moisture in the atmosphere and hover along the ground on a humid day.

The location of the release is another major environmental consideration. Whether it is inside or outside a structure is very important, depending on the material. If a vapor release occurs outside a building, the vapor clouds may dissipate in the air, whereas a similar hazmat release inside a building may result in a higher concentration of the material. This is particularly important for materials such as anhydrous ammonia, which has a lower explosive limit (LEL)-upper explosive limit (UEL) range of between 15 and 28 percent (NIOSH Pocket Guide to Chemical Hazards) and presents an additional hazard when concentrated and unable to disperse.

On the other hand, a building may contain the release so that the material will not travel out into the surrounding community. The spill’s location relative to waterways and sewers is a very common environmental consideration, since the material ideally must be confined to the area of origin.

Access to the incident location may also be a problem. For example, many rail lines run through areas where there is no easy road access. A container that has fallen down a hill may be relatively difficult to access, but a leaking container located uphill along your approach path presents a completely different problem.

The environment consideration dictates who or what may be in harm’s way, but further assessment of the container and material will indicate the likelihood of the harm coming to them.


The container design is analogous to building construction in structural fire size-up. Like buildings, each type of container has its own important features. General container assessment includes type (railcar, tank truck, intermodal container, drum, fixed tank, pipe, and so forth), size, shape (e.g., pressure or nonpressure vessel), construction, condition, and documents or markings associated with the container.

Each class of container has its unique features, which are often governed by regulations. For example, the common gasoline tank truck has a distinctive shape and safety features such as rollover protection, internal valves, and remote valve shutoffs. It may have several compartments and thus may be carrying multiple products.

On a railcar tank, the location of valves and the type of dome may indicate the type of product it contains, even if labels, placards, or other markings are not visible. A railcar may additionally be equipped with head shields, thermal protection, or a protective jacket that can be identified by careful observation or understanding the railcar’s markings.

These features may be very important in an emergency response. A protective jacket around the container may offer additional container protection but also makes locating a leak more difficult and limits access, which is significant when cooling water must be applied.

Pressure-controlling devices help protect the container from rupture or collapse. A pressure-relief device offers some protection from rupture from excess pressure, whereas a vacuum breaker prevents a tank from collapsing under low-pressure conditions. Most firefighters are familiar with propane cylinders and the importance of the pressure-relief device (photo 1).

(1) Further details can be added to the size-up scheme as needed. For example, on this overturned propane truck, an attached relief device is part of the container’s protection system. In this case, if the container were under additional stress, would the relief device operate? What kind of relief device is present? In this position, would it vent from the vapor space or the liquid space? (Photo courtesy of Delaware Department of Natural Resources and Environmental Control.)

Drums, however, typically do not have pressure-relief devices and may catastrophically fail under stress, sometimes rocketing through the air as a result. Knowing the container type gives you some idea of the quantity and type of material that may be involved and where and how leaks and failures commonly occur and may generally provide valuable information that influences tactical decisions.

Assess the container’s condition for damage and for stresses acting on the container, such as thermal, chemical, or mechanical stress. They may interact differently on each type of container. The gasoline tank truck mentioned above is constructed of aluminum, which has a relatively low melting point and so may fare rather poorly in the presence of the thermal stress of a fire. A DOT 412 tanker would hold up much better under these conditions because it is made of a heavier gauge steel. Mechanical stress on the container includes anything that pushes or pulls on the container, such as pressure, bending, crushing, and twisting. Chemical stress occurs when the hazardous material interacts with the container, softening or corroding it. It is critical to identify stress on the container; if stress overcomes the container, a breach can occur. Some indications of increasing stress to the container include sounds, movement, additional cracking, and more frequent or violent venting. Although these warnings are not always present, heed them when they are.

The nature (holes, cracks, gouges, scores, or dents), extent, and location of container damage are among the main points in container assessment. One case where the location of the damaged portion of the container is especially important is when the damage crosses a weld. Knowing the materials of construction and how they react to damage will help to evaluate the condition of the container.

Placards, labels, other markings, and documentation are also associated with the container; they indicate the material that is inside. It is essential to obtain documentation, such as shipping papers, at a hazmat incident; it can often be used to identify what materials are present, even though some of the materials cannot be directly observed at the time.

Assessing the container and any stress still acting on it is important in estimating the likelihood of container failure, a key element in determining the magnitude of the problem.


In assessing the hazardous materials involved, it is as essential to understand the physical and chemical properties as it is to identify the extent and location of a fire in a structure. The material’s chemical properties determine what it does or what the mechanism of harm is. The mechanism of harm helps to determine what type of personal protective equipment is required for anyone directly exposed to the material. The basic mechanisms of harm include energy release (fire, explosion, chemical reaction, or radioactivity), corrosiveness, and toxicity.

Fire is one of the most common hazards encountered when dealing with hazardous materials. In assessing a fire hazard, consider the material’s flash point, the extent of its flammable range, where the lower flammable range starts, and the ability to control available ignition sources. If the material is above its flash point, it is giving off enough vapor such that a flammable environment can exist. Even if the air temperature is below the material’s flash point, the material may be in a location that is above the flash point-for example, on blacktop in the sun. The environment of the spill (indoors vs. outdoors) greatly influences whether the required concentrations are likely to be present. The presence of other materials, such as oxidizers, can greatly increase the fire hazard a material presents (photo 2).

(2) The ambient temperature and flash point of the hazardous materials involved affect an incident’s severity. This car collided with the tractor trailer and ruptured the truck’s saddle fuel tank containing diesel fuel. A car fire fueled by the car’s gasoline ensued in the middle of a large puddle of diesel fuel. However, because the ambient temperature was near freezing and responders quickly knocked down the car fire, the spilled diesel fuel never ignited because it never reached its flash point of around 140ºF. [Photo courtesy of Mill Creek (DE) Fire Company.]

Fire hazard is simply the most common reactive hazard. Other chemical reactions can also pose problems. Many chemical reactions are exothermic, or produce heat when the reaction occurs. Reactions may also produce gases, which add pressure to the system. Explosions are an extreme example of a reactive hazard in which the reaction is extremely fast and gases are given off, producing a pressure wave. Any energy put into the system can increase the hazard. For example, sulfuric acid, which normally has very little vapor pressure, can be converted into a mist, which presents a mobile airborne hazard. Even though it might not be directly observed, it is critical that responders understand the energy of the system as it impacts the environment, the container, and the materials involved. Energy is what causes harm.

Corrosive materials include U.S. Department of Transportation (DOT) hazard classes 8 (corrosives), 5 (oxidizers), and 2.3 (toxic gases), which can damage living tissue, metals, or other materials. Important considerations for this class include the concentration of the corrosive material and the chemical strength of the material. The chemical strength is the inherent strength of the acid, base, or oxidizer. Sulfuric acid is a stronger acid than hydrochloric acid, which is stronger than phosphoric acid (in soda) and acetic acid (in vinegar). Any of these materials can be diluted to a low concentration. You can often detect corrosive materials using pH paper. Some corrosive materials are also toxic.

Toxic materials have a variety of effects, depending on the nature and the amount of the material. A toxic environment can result from the presence of a toxic material or the absence of oxygen. The release of a large amount of material, even one not normally considered toxic (such as nitrogen), can result in asphyxiation. The key to a toxic exposure is the dose received, so avoiding contact or performing rapid decontamination if contact has occurred is the most important action at an incident involving toxic materials. In general, toxic materials can disrupt the structure of body tissues and change the rate of normal body functions. Assessing and measuring toxicity is relatively difficult, so the key to understanding the hazard is to identify the material or class of material and consult references for guidance.

Physical properties play a large role in the material’s behavior and help to determine the type of PPE required for handling the material. The most important physical properties address the material’s mobility. For example, among the physical states of materials-solids, liquids, and gases-gases are the most mobile, requiring larger exclusion zones and higher levels of personal protective equipment. Likewise, materials that have a high vapor pressure or give off relatively large amounts of vapor also require a more cautious approach. Vapor pressure increases with temperature, so consider the local environment along with the standard room temperature value listed in the references. Other physical properties such as solubility, vapor density, and specific gravity play key roles in developing a material-management strategy, as in the assessment example in the box above.

Solubility is another key physical property, since it determines the tactics such as decontamination, material control, and the use of foam for firefighting. Materials that are highly water soluble are relatively easy to remove using water, and an escaping vapor cloud may be absorbed into a fog stream. Conversely, it is very difficult to control a water-soluble material if it reaches a waterway, since the entire water stream would be contaminated. Water-soluble materials are generally polar, which requires a different proportion of foam if it is used for vapor suppression or firefighting.

Vapor density and specific gravity are related physical properties that affect the air-monitoring/detection strategy and the material-management strategy. Materials with a vapor density of less than 1 (1 = air) rise, so detection activities should be concentrated on the higher elevations of the incident. Conversely, materials that are heavier than air will sink and tend to accumulate in lower places. Specific gravity is similar in that an insoluble liquid with a specific gravity less than 1 will float on water, including water in a decontamination pool. In this case, an underflow dam or a boom to absorb the material from the water’s surface are two possible material-management strategies. When materials are heavier than water, they can be concentrated using an overflow dam. There are many other physical properties, and the assessment tree can be expanded to handle them when they become important to a response.

An example of where understanding both the physical and chemical properties of the material is critical is in the development of an air-monitoring strategy, one of the key items at any hazmat incident. You can identify initial hot, warm, and cold zones using initial observations and references, but determine the actual location of the material through monitoring. The chemical properties determine the type of equipment you will need. For example, for flammable materials, use a four-gas or LEL combustible gas detector; for corrosives, use pH paper; and to detect very low levels of toxic materials, use a photoionization detector, flame ionization detector, other specialized detector, or colorimetric indicator. The physical properties determine where to look for the material and whether the material is in a form the detectors can find. Suppression or rescue units should be able to perform some basic air monitoring, particularly in the case of flammable or corrosive materials. Common incidents where this occurs include gas leaks and motor vehicle collisions. Air monitoring is also essential when performing decontamination, to ensure that the hazardous material has been removed. A hazmat technician will perform air monitoring, looking for the location, identity, and quantity of material. To do so, the technician must understand the material and know how and where to find it.

The material’s physical properties give clues to the movement of the material and, hence, the probability of coming in contact with the material. The chemical properties of the material dictate the consequences of coming into contact with the material. These are the keys to understanding the material’s behavior, much like understanding the smoke and fire behavior at a structural fire incident.

. . .

Understanding the nature of the incident is the key to safe and expedient resolution. Careful consideration of the environment, containers, and materials-including things causing additional stress on the system-will lead to identification of strategic priorities and concerns. Investigating further levels of detail in each of these areas will provide guidance on tactics for safely resolving the incident.

Material Assessment Example

Material: 4,4’-Diphenylmethane diisocyanate (MDI).

Chemical property: Toxicity – LC50 (4 hr, male rats) = 36 ppm.

Conclusion: Highly toxic material. Very little vapor exposure causes death in 50 percent of the exposed rats.

Physical property: Vapor pressure (at 77°F) = 0.000005 mmHg.

Conclusion: Very low-vapor pressure material. Contact with a significant amount of vapor is not likely under normal conditions.

KRISTINA A. KREUTZER is a research chemist at the DuPont Experimental Station, a member of its emergency response team, and a captain with the Mill Creek Fire Company in Wilmington, Delaware. She has a bachelor’s degree in chemistry from the University of Maryland and a Ph.D. in chemistry from the Massachusetts Institute of Technology. Kreutzer is a certified firefighter I and II, fire officer I and II, fire instructor I and II, hazardous materials technician, and National Registry Emergency Medical Technician-Basic (NREMT-B). She is a hazmat instructor with Delaware State Fire School and a member of the New Castle County (DE) Technical Decontamination Team and the New Castle County Industrial Hazardous Materials Response Alliance.

No posts to display