Identification will often be difficult in roadway incidents. However, once identification and the more important verification of the identification has occurred, someone must find out what the material is and how it might hurt us, the public and/or property.
Imagine this. You are the Incident Commander (IC) and you call your Level A Recon team who is telling you the name of the product, which you cannot understand. The Recon team states they will spell it phonetically. “Mike, Echo, Tango, Hotel, Yankee, Lima, Echo, Tango, Hotel, Yankee, Lima, Papa, Hotel, Oscar, Sierra, Papa, Hotel, Oscar, November, Oscar, Tango, Hotel, India, Oscar, Lima, India, Tango, India, Charlie [SPACE] Alpha, Charlie, India, Delta.” At this point, you may wish you were assigned to decontamination instead of serving as the IC. The team spelled MethylEthylPhosphonothiolitic Acid. OK, we verify with the shipper, receiver, or someone to be sure that the trailer or container is marked correctly and now it is time for the Hazmat Research/Science Officer to tell us what the heck that even is.
If you are assigned the position of Hazmat Research/Science Officer, you must be able to interpret the research material’s characteristics into plain language so that strategies and tactics can be developed to deal with the product. We must also remember that research materials may list different values for each property. We must consult at least three different sources and use the worst case scenario of what is listed.
For example, if one source lists that your material will detonate anytime it reaches 84 degrees Fahrenheit, another source lists the temperature at 75 degrees Fahrenheit, and a third lists the temperature at which detonation will occur at 60 degrees Fahrenheit, we must use the 60 degrees as the worst case scenario. Each source may have used independent testing and if anyone was able to make the material we are dealing with detonate at a lower temperature than the other sources list, we want to use that value just in case Murphy is riding along with us that day — as he often does.
Let’s start with a simpler product, gasoline. First, let us look at the chemical formula which is often one of the first things you see on many of the research sources. Gasoline’s chemical formula varies slightly with the octane rating and purity. It could be C6H18 all the way up to C8H26. In the first compound, this means that there are six molecules of Carbon and 18 molecules of Hydrogen, which we know is highly flammable (see Hindenburg disaster, May 6, 1937). So, out of the gate here, we would expect our hazardous material (gasoline) to probably be highly flammable, even if we didn’t know anything about it.
Many sources will also list a CAS (Chemical Abstract Service) number. These numbers are assigned to unique chemicals. Do you ever notice that when you look up a number in the Department of Transportation Emergency Response Guidebook that several chemicals may be listed? This is not the case for CAS numbers. Each chemical has a unique CAS number. Next, we want to see what the physical property of the material is. This is sometimes listed as, “a clear, colorless liquid” or as “a colorless gas with a pungent odor.” If we do not see a description, we need to examine the chemical properties.
Flash point will tell us the temperature at which a material can vaporize to form an ignitable mixture in air given an external ignition source. For gasoline, the flash point is 45 degrees below zero Fahrenheit. This means unless we are standing on the North Pole in January, it is likely warm enough outside for our liquid to be generating sufficient vapors to ignite if an external ignition source is present. If a flash point is not given for our material in our reference, we can assume that it is either already a solid or gas under normal conditions, or has not been tested. Our explosive limits (often listed as “UEL” – Upper Explosive Limit and “LEL” – Lower Explosive Limit) will tell us the concentrations in air that allow the material to burn. These are normally listed as percentages but can easily be converted to parts per million (ppm).
Gasoline’s upper explosive limit is 7.6 percent and the lower explosive limit is 1.4 percent. This is the equivalent of 76,000 ppm and 14,000 ppm (as 1,000,000 ppm = 100 percent concentration in air). In concentrations below 1.4 percent, gasoline is too lean to burn in air and in concentrations above 7.6 percent; gasoline is too rich to burn in air. Narrow explosive limits represent less of a risk of fire. Wide explosive limits (Ethylene Oxide has a LEL of 3 percent and UEL of 100 percent) represent a material that can explode or burn under virtually any concentrations. Specific Gravity will tell us the weight of the liquid when compared to water (which is equal to one). So, specific gravities greater than one will sink in water and specific gravities less than one will float in water. This is helpful if we intend to construct underflow or overflow dams. If we do not see a specific gravity value in our reference source, we can assume that it is either a solid or gas under normal conditions, or that source’s publisher may not have tested the material.
Vapor Density is similar and tells us the weight of a vapor when compared to air (which is equal to one). Vapor densities greater than one will sink in air and hug the ground, which makes their movement more dependent on topography. Vapor densities less than one will rise in air and makes their movement more dependent on prevailing winds. Gasoline has a specific gravity of 0.72 which means it will float on top of water. This is why water does not work to extinguish gasoline fires. Water simply carries the burning gasoline wherever the topography takes them both. Foam is necessary to sit on top of the burning gasoline and smother, cool and separate the fuel from oxygen. When using foam, we must know at what percentage to apply it to the material. Solubility of the material should be examined in our reference sources.
If our hazardous material is soluble (sometimes defined as water miscible), then it is a polar solvent. If our material is insoluble (sometimes defined as water immiscible), then it is a hydrocarbon. Gasoline is insoluble in water and is therefore a hydrocarbon. Hydrocarbons get three percent concentration of Aqueous Film Forming Foam (AFFF) and Polar Solvents get six percent concentration of AFFF. But remember for every 100 gallons, even at six percent concentration, AFFF is still 94 gallons of water and six gallons of foam concentrate (the stuff in the buckets). So if our material is incompatible with water or water is not recommended as an extinguishing agent, then AFFF is very likely not appropriate either.
Next, we want to examine our boiling point and vapor pressure. These two properties have some correlation. Water has a boiling point of 212 degrees Fahrenheit and a Vapor Pressure of roughly 20 millimeters of Mercury (mm Hg) at room temperature (whatever room temperature is — consider it 72 degrees Fahrenheit). Consider the ring of water around the drink you leave on the table in the kitchen. It stays for a while but over the period of an hour or two, it vaporizes and evaporates. While we do not normally think of water giving off vapors, we know it is capable of vaporization even at “room temperature.” We also know when we boil water to 212 degrees Fahrenheit, we get steam. Vapor pressure will rise with increases in temperature. At 212 degrees Fahrenheit, the vapor pressure of water is 760 mm Hg. This number should be familiar as 760 mm Hg is equal to 14.7 psi (atmospheric pressure at sea level). When water reaches that temperature and vapor pressure, neither continue to rise as the liquid is converted to vapor. Boiling points that are very low in temperature and vapor pressures that are much higher than atmospheric pressure (760 mm Hg) represent volatile materials that give off a large amount of vapors. Extremely high boiling points and low vapor pressures are present in materials that do not readily vaporize.
Ethylene Glycol (antifreeze in internal combustion engine radiators) has a vapor pressure of 3.75 mm Hg at room temperature. This liquid will hang around a while as a liquid and requires higher temperatures to readily become a vapor. Conversely, Chlorine has a vapor pressure of somewhere between 4,800 and 5,200 mm Hg. This is largely above atmospheric pressure (760 mm Hg) and means we will almost always see Chlorine in gaseous/vapor form. Remember, just because a material’s vapor pressure is below atmospheric pressure (760 mm Hg) does not mean that it does not generate vapors. Lower vapor pressures just mean it takes much longer to vaporize (remember the water ring on the table).
Gasoline has a boiling point of 102 degrees Fahrenheit and a Vapor Pressure of 38 to 300 mm Hg. This means that vapors will likely be present; however, we should still see liquid (especially on colder days). Most reference sources do not list a vapor density value since gasoline is considered a liquid. It is also possible that we would see a vapor pressure for a solid in our reference materials. If this occurs, we are dealing with a material that is capable of undergoing sublimation. Sublimation is when a material moves from a solid state directly to a gas state without becoming a liquid first. Napthalene (mothballs) is an example of such a material.
Finally, we want to examine the way by which the material hurts the public or us. These values are often reported by different agencies using different terms. The Environmental Protection Agency (EPA) uses Acute Exposure Guideline Levels (AEGLs) often called “Eagles.” The U.S. National Institute for Occupational Safety and Health (NIOSH) uses Immediately Dangerous to Life and Health (IDLH). NIOSH will also use a recommended exposure limit (REL) while OSHA uses a permissible exposure limit (PEL). Additionally, the American Industrial Hygiene Association uses Emergency Response Planning Guide (ERPG) values at three different levels. In each of these terms are values that represent concentrations that are unsafe for unprotected individuals. They all have one thing in common. The lower the reported value, the more dangerous the material. Values may appear as parts per million (ppm) for liquids and gases/vapors or milligrams per cubic meter (mg/m3) for solids. Gasoline possesses more chronic health hazards than acute, aside from catching fire and burning you. However, the ERPG-1 (the level below which you can sustain exposure for one hour without adverse health effects) is 200 ppm.
For comparison, at 10 ppm, Chlorine is immediately dangerous to life and health (IDLH) requiring prompt evacuation of unprotected individuals. The lower reported number for Chlorine represents less of a concentration it takes to hurt us. Therefore, Chlorine is a more dangerous chemical than gasoline when considering health hazards.
We must also consider how the material enters our body when we select our personal protective equipment. Materials that harm us through skin absorption require fully-encapsulating (Level A) suits. Materials that are a splash hazard and a mild respiratory hazard may require a reduced level of protection (Level B or C).
Let’s take what we have read here and go back to our Methyethylphosphonothiolitic Acid. This is the military nerve agent called VX. It has a boiling point of 568.4 degrees Fahrenheit and a vapor pressure of 0.0007 mm Hg. This means that unless it is aerosolized mechanically, this material will likely be a liquid. Any vapors produced will be slow forming and this material will be very persistent (by design). It has a specific gravity of 1.008 — approximately the same weight as water — and is soluble in water which makes it and water a perfect match (by design). Its flash point is 318.2 degrees Fahrenheit which makes it difficult to burn (by design). Its vapor density is 9.2 which makes any vapors present much heavier than air. The level at which it is immediately dangerous to life and health is 0.003 mg/m3 which given its molecular mass is equal to 0.072 parts per million (ppm) or 72,000 parts per billion (ppb). So the level at which VX can kill you is about 0.0000072 percent concentration in air. That’s not much.
Continue to research the terms associated with chemical properties, particularly for chemicals being used in fixed facilities in your jurisdiction. Remember, understanding a chemical’s behavior is easy once you understand what each chemical property describes. However, you cannot help anyone if you have researched a material for 20 minutes, and it turns out to be the wrong chemical. Insure that identification and verification have occurred. Recognize any red flags that may occur from the research sources to the hot zone.
If the entry team is reporting heavy vapor concentrations and the material you are researching has a boiling point of 1,000,000 degrees Fahrenheit and a Vapor Pressure of 0.000000001 mm Hg, then you are either on the wrong page in the book or the entry team is at a different call than you are. The research/science job is often unappreciated. But the information gathered during this process can be critical. This author’s chief once entered the command post during the eighth hour of a hazmat incident involving an overturned gasoline tanker that was not leaking and stated, “These hazmat calls sure are boring.” Your author here replied, “Yep, just the way I like them.” Proper research and understanding the science can prevent all of us from “creating” exciting hazmat calls.
Be safe and do good.