Haz-Mat Survival Tips: Stages of a Hazardous Materials IncidentBeyond the Rule of Thumb
Survival Tip 23
By Steven De Lisi
Hazardous materials generally present little threat to first responders and those who handle the material unless there is an unintended breach of a container resulting in a release of the material. Containers of hazardous materials are typically breached as a result of internal pressure created by exposure to excessive heat; a chemical reaction of the contents that causes an increase in pressure or deterioration of the container; or mechanical damage, such as when a container strikes an object with force or it is struck by another object, as when punctured by a forklift blade.
Regardless of the type of stress applied to a container, first responders will find that hazardous-materials incidents can often be divided into three stages, each stage with its own unique challenges. These stages are
Containers with an on-going release
Containers with the potential to release their contents
Containers that have already released their contents
Determining the stage of a hazardous-materials incident should be included during the initial size-up and hazard assessment by those first to arrive at the scene of a hazardous-materials incident. By doing so, first responders will be better able to determine just how aggressive they should be in attempting to manage the incident. For example, incidents involving a container with an ongoing release may require quick action to contain the spilled material, whereas those involving containers exposed to heat or a chemical reaction with the potential to release their contents (often as a result of the container's bursting) may require a rapid evacuation of all persons in the affected area. However, when dealing with incidents involving containers that have already released their contents prior to the arrival of first responders, there may be little that they need to do to improve the situation other than to isolate and deny entry to the spill area.
Although there are specific concerns for each stage of a hazardous-materials incident, first responders should remember that the stage can change throughout the course of an event, thereby presenting a combination of challenges to the safe handling of the incident.
Containers with an ongoing release
Incidents involving containers with an ongoing release may be the result of mechanical damage to the container or valves, or exposure to heat, which has activated a pressure relief device. In this stage, first responders are faced with three considerations:
Behavior of the hazardous material based upon its physical state.
Stopping the release.
Containing the release.
The physical state of a hazardous material may be solid, liquid, or gas. For first responders, a gas is the most difficult form of material to deal with since containment, especially outdoors, is difficult. However, solids and liquids can create dust and vapors respectively, and they present the same containment difficulties as any gas.
To contain the release of liquids, first responders are usually taught how to construct temporary barriers using soil, granular absorbents, or specially designed absorbent booms. When using any of this containment equipment, the following questions must be asked:
Is containment equipment available at the scene?
Will the containment medium react with the hazardous material?
How much material has already been released?
How much more material will continue to be released?
The importance of estimating the size of the release is critical to ensure that containment areas are of adequate capacity. For example, retention basins created to contain the release of a liquid hazardous material may need to be pumped out during the course of an incident to avoid overflowing. Remember that the time to order a vacuum truck for this purpose is long before the liquid reaches the top of the basin.
When dealing with cargo tanks, some first responders may assume that all have multiple compartments, so that a tear in one compartment will result in a release from only that section of the tank. However, some cargo tanks may be what are sometimes referred to as a "single shot" tank, meaning that the tank is open from end to end and a breach in any one portion of the tank could result in the release of the entire contents.
The release of a liquid from a container will usually subside when the level of the liquid reaches the level of the breach. Although some first responders may then assume that the leak may then subside, the reality is that as the liquid level in a container changes, the center of gravity changes as well. For containers resting solidly on level ground, this is of no consequence. However, for those found in an unstable configuration, such as a cargo tank that has overturned down an embankment, the position of the container may shift as the liquid level drops, thereby continuing to lower the breach below the liquid level and allowing the container to leak long after first responders believed it would stop.
The potential for some containers of hazardous materials to shift position during an incident can pose a severe threat to first responders working nearby. In these situations, it is important to stabilize containers. This can be accomplished with wooden blocks for individual containers such as drums or securing large vehicles with cables from a wrecker truck or crane.
Access to containment equipment is often a challenge for first responders. For many departments, this equipment is normally not carried on first-due apparatus but is often relegated to a small trailer or special utility truck. Unfortunately, the arrival of these trucks and trailers is usually delayed, forcing first responders to use makeshift means for containment.
In the absence of absorbent booms, you can sometimes construct an underflow dam by using a small section of plastic pipe, but since this pipe is likely carried on the same truck or trailer as the booms, you may have to use a section of hard suction hose instead. Always remember that, for booms or underflow dams to be effective, the hazardous material to be contained must not mix with water and it must float on the surface.
Containers with the potential to release their contents
Containers of hazardous materials that have not released their contents do not normally present a danger to first responders unless there is the threat of a chemical, thermal, or mechanical stress that can affect the integrity of the container. Potential sources of mechanical stress include situations such as the structural collapse of a building, a tank resting in an unstable position with the potential to fall, or first responders handling a container. As mentioned previously, chemical and thermal stress can increase internal pressure; and if the container is not equipped with a pressure-relief device, as is the case with most containers of liquids, the increase in pressure can cause the container to burst with great force.
Remember that thermal stress is not just the result of exposure to fire, but also can be caused by ambient temperature and exposure to direct sunlight. Depending on the location of the incident and the time of year, there can be wide fluctuations of outdoor temperatures during the course of an incident.
There can always be a combination of stressors acting on a container, and they can present unique hazards to first responders. In particular, a container that has already been weakened by mechanical damage may fail sooner if subjected to an increase in internal pressure from subsequent chemical or thermal stress.
For containers equipped with a pressure-relief device, there may be less of a chance of the container's exploding from this excessive internal pressure. However, the effectiveness of a pressure-relief device may be compromised by mechanical stress to the container, since the amount of pressure a damaged container can withstand may be less than the setting of the pressure-relief device, meaning that the container may burst before the pressure-relief device opens--or even while the device is in operation.
Chemical stress includes situations in which certain types of corrosive material stored in lined metal containers attack the container wall because of lining failure. Chemical stress can also occur when certain materials are mixed, such as when employees in the act of disposing of hazardous waste place material in the wrong container or when a rail car containing a small amount of liquid residue is filled with another, incompatible material.
Thermal stress can sometimes be relieved by cooling containers with water or moving them from the source of heat exposure. You must first consider the potential of hazards to first responders should the containers burst before undertaking these activities. In some situations, first responders may instead decide that a retreat to safety is in order.
Likewise, removing all persons from an affected area may be the best approach when dealing with containers subject to chemical stress, since there is most likely very little first responders can do to correct the situation. Allowing the container to burst with all persons withdrawn from the area or waiting for the chemical stress to relieve itself may be the only ways to safely stop the increase of internal pressure.
Containers that have already released their contents
Incidents in which containers have released their entire contents prior to the arrival of first responders usually involve small containers such as those intended for use by consumers. Examples include one-gallon and five-gallon containers, paper bags, plastic containers, and cardboard boxes. Since they are intended for ease of handling, the volume and weight are usually limited, yet the very fact that these containers are designed to be handled invites the potential for them to be dropped or otherwise exposed to mechanical stress.
These incidents typically result in a relatively small release of product when compared to bulk tanks, yet first responders must remember that five gallons of material can still have a significant impact--for example, if it were spilled into a waterway. Likewise, a jar of pesticide concentrate may contain very little product, yet the potential for extreme toxicity is a real threat that cannot be underestimated because of the small size of the release.
There are two advantages to first responders when dealing with containers that have already released their contents: (1) They can usually visualize the amount of material released and are therefore are better able to estimate potential exposure and determine the size of a containment area; (2) there is no need to deal with the hazards of an ongoing release or an incident with a potential for release mentioned previously. Furthermore, unless the material is migrating from the incident scene, such as on a sloped surface moving towards a drain, there may be little first responders need to do to contain the material. Of course, although some first responders may be content with this fact, remember that incidents occurring outdoors are subject to environmental factors, most notably rain, and that a sudden storm moving through an area can turn a relatively minor spill involving five gallons of paint into a fast-moving nightmare that needs to be contained in a manner that is no different than handling an ongoing release from a cargo tank.
The stage of a hazardous-materials incident should always be a factor when determining the level of involvement of first responders attempting to resolve the incident. Of all the stages, remember that the most critical is the one in which first responders are faced with a container without an active release on arrival. All too often, first responders may be lulled into a false sense of security, yet there may be disastrous consequences unless they determine early in the incident the potential for the container to release its contents and take the appropriate steps to protect themselves and the public.
Click here for more info on Steven De Lisi's book, Hazardous Materials Incidents: Surviving the Initial Response.
Steven M. De Lisi retired after a fire service career spanning 27 years that included serving as a regional training manager for the Virginia Department of Fire Programs (VDFP) and most recently as the deputy chief for the Virginia Air Guard Fire Rescue. De Lisi is a hazardous materials specialist; he continues to coordinate a statewide training program for the investigation of environmental crimes as an adjunct instructor for VDFP. De Lisi began his career in hazardous-materials response in 1982 as a member of the hazmat team with the Newport News (VA) Fire Department. Since then, he has also served as a hazardous materials officer for the Virginia Department of Emergency Management; in that capacity, he provided on-scene assistance to first responders involved with hazardous-materials incidents in an area that included more than 20 local jurisdictions.
December 23, 2007
