David A. Greene

Published Writing - Fall 2007

Haz Mat: Basically Stable or Pop Rivet???

This quarter, we are discussing hazardous materials. One of the benefits of teaching the hazardous materials technician course for the South Carolina Fire Academy is that I have the opportunity to interact with other instructors, many of whom, are very knowledgeable in the haz mat world. 

A friend and fellow instructor, who we will call David also (to protect the innocent), submits that most haz mat calls are routine or as he describes it, Basically Stable. I can only assume that is what the abbreviation that he uses stands for. Moreover, David outlines that modern passenger airplanes are assembled using composite materials and are joined using thousands of pop rivets. Pop rivets routinely fall out of airplanes in flight and with roughly 87,000 flights a day over the United States, we all are constantly exposed to falling pop rivets. Very few of us probably know someone who can tell the story of walking through the mall parking lot and being beaned in the forehead by a pop rivet falling from a passing airliner at 35,000 feet. David is exactly right, although the bulk of haz mat calls are routine, we must always be prepared for when that “pop rivet” haz mat call hits us. These types of calls can stress any department beyond its limits and require more resources, commitment from personnel, and interaction with many other agencies than any other type of call we encounter.

Identifying the material involved is paramount and is often the most difficult task. Identification drives everything in our operation: our suit selection, the air monitoring and detection equipment to be utilized, the confinement and containment techniques, the type and size of our decontamination, everything. In fixed facilities, we have an edge in “the game”. We should already know, based on our pre-incident surveys, what materials are used in our fixed facilities. A haz mat release in this situation will likely be one of the materials used at the facility. Determining which one may be our only obstacle in the operation. This is our plight on the railroads as well, as a list of transported materials can frequently be obtained from the rail company in the event of a release. 

In road transportation, however, we often enter “the game” after half time and down by four touchdowns. Covering 200 miles of highways, including 28 miles of Interstate 95, the department in which I work is frequently tasked with interacting with tractor-trailer accidents and fires. In my experience, the truck drivers have been a little less than helpful. One sifted through ten sets of shipping papers until he finally resigned himself to not knowing, another had no shipping papers and spoke only Spanish (and was more fluent than the six semesters at the College of Charleston made me . . . probably because the College of Charleston required me to take only four semesters and I didn’t take the additional two for extra credit). My personal favorite truck driver, is the guy who when questioned of what he is transporting while we both admire his burning tractor and trailer tells us, “I don’t know, but it’s bad.” With this ever-increasing disadvantage in mind, we must find another way to identify materials and to improve our position, tactically. 

We will assume that an isolation perimeter has been established and we have begun our process to determine if this call is basically stable or a pop rivet. Let’s start with what state the material (chemical) is in. Is it a solid, liquid or gas? Although there are solids out there that are very reactive, or as David would say, “very unhappy chemicals”, solids are easiest to control. Liquids on the other hand are more difficult to control and can frequently enter places where we don’t want them (i.e. sewers, water supplies, etc.). Gases are impossible to control, at least outdoors, and are often the causes of the most injuries in frequency and severity. We take the information regarding the state of the material and use it along with other information to determine what it is.

Do we have any victims? If so, they can tell us a lot about the material, even if they are unconscious. First, let’s look at the magnitude of the event and the location. A farmer can inhale a very toxic hazardous material alone at home without the incident appearing to be serious, at least to everyone but the farmer. However, the same material released at the mall on the day after Thanksgiving should generate many more patients exhibiting the same signs and symptoms. In this case, we are likely dealing with a gas that affected a large number of people, especially if our patients present with a chief complaint of respiratory distress or apnea. In the presence of only one patient in a location that has the potential for many more, we should consider that our patient possibly ate or drank something they shouldn’t have or absorbed a material through their skin, especially if their chief complaint is nausea and vomiting. This in turn means we are dealing with a solid or liquid, and therefore something that is easier to control. Was our patient burned by a corrosive? If so, are the burns a soapy sloughing off of the skin, which is indicative of a base or alkali. If the burns have hard scabs with blisters, an acid likely burned our patient. 

We should always use our air monitoring and detection equipment to help us determine the material. Don’t be fooled by our patients’ signs and symptoms. When alerts were issued that crop dusters would be used to spray organophosphate (pesticides) on large numbers of people, our enemy’s plan included lacing the organophosphates with radium (a highly radioactive material). We monitor for radiation first, always. In the above case, patients that present with bradycardia, hypotension, dyspnea, nausea and vomiting, incontinence, miosis (pupil constriction), lacrimation (tearing of the eyes), salivation and diaphoresis may very well have been exposed to an organophosphate or a nerve agent, but remember it is still necessary to pull the radiation detectors off of the truck each and every time. Remember, we have no defense from radiation other than time, distance and shielding. Unfortunately, we live in a world now where what we see may not always be what we have. Don’t forget to monitor for radiation first. We monitor for flammability second, which is also very important for those of us that don’t want to be shrink wrapped while wearing our plastic Level A (body bag with the window) suit. Flammability monitoring can be accomplished using any number of detectors but keep in mind that significant changes in the oxygen level will greatly affect your flammability readings. Also, monitoring for corrosivity early, using Ph strips or paper, can save your other monitors from being destroyed by corrosive vapors. Third, we monitor for oxygen. This is a very important step. Responders will typically have their own air supply when entering; however, increases in oxygen above normal levels could show the presence of an oxidizer and decreases in oxygen below normal levels could show the presence of another material that is displacing the oxygen. Finally, we monitor for toxicity, but that typically involves using chemical specific monitors. At that point, we have to have an idea of what the material is in order to determine the appropriate chemical specific monitor to use.

Next, we use our reference materials to determine the material. So what do all those numbers mean? When looking at a material’s IDLH value (or the amount of a chemical that is immediately dangerous to our life and health) we hope to see a high number. The higher the reported IDLH value is, the more of the material it takes to hurt us. The lower the IDLH value is, the less it takes to hurt us. These are typically reported in parts-per-million (ppm). One million parts-per-million of a material would be 100% concentration in air. Therefore, one-tenth of one percent concentration in air is equal to 1,000 ppm. As stated above, if we notice our oxygen level has gone from normal 20.9% to 20.8%, that means that one-tenth of a percent of oxygen or 1,000 ppm has been displaced by something else. The IDLH value for Chlorine is 10 ppm, so if this was the material we were faced with, we would already be 100 times higher than the minimum amount that can cause us harm by the time we noticed the change on our oxygen meter. 

The boiling point and vapor pressure of our material, which are directly related to each other, is also something else we need to read about in our reference materials. If the material is a liquid, when it is heated to its boiling point it will become a vapor (or gas). Think of water (H-2-O). Below 32 degrees Fahrenheit, it is a solid (ice). When it reaches its melting point of 32 degrees Fahrenheit, it becomes a liquid (water), and again changes state when it reaches 212 degrees Fahrenheit, to become a vapor (gas). Boiling point is the temperature at which the substance will change from a liquid to a gas at a given pressure. Vapor pressure of a liquid is the pressure exerted by its vapor when the liquid and vapor are in dynamic equilibrium. All liquids produce vapors to some degree. Remember pumper operations class, what is normal atmospheric pressure? It is 14.7 psi at sea level, which is equivalent to 760 millimeters of mercury (mm Hg). As reported vapor pressures approach 760 mm Hg, the more readily they will vaporize. Materials with high vapor pressures are considered volatile and will form a high concentration of vapor above the liquid. Gasoline, which has a boiling point of 32 – 210 degrees Celsius and a vapor pressure of 304 – 684 mm Hg, readily produces vapors above its liquid. If you put a bucket of gasoline in a vacuum or otherwise eliminated its vapors and stuck a burning match in the liquid, the match would go out (don’t try that at home). Water has a vapor pressure of approximately 15 mm Hg at room temperature. If you heat water to 212 degrees Fahrenheit, its vapor pressure at that temperature is 760 mm Hg and is therefore no longer a liquid. Even at 15 mm Hg, vaporization does occur, however slowly. What happens to the ring of water left by your cold drink left on a table in the day room? When you remove your drink from the table, over the next hour or two, the ring disappears. This is not visible such as when you heat a teakettle to 212 degrees Fahrenheit and can watch the steam (vapor) escape from the top. When examining boiling points and vapor pressures in our research materials, we hope to see a high boiling point and a low vapor pressure, as this is indicative of liquids that do not readily vaporize or change states to a gas. A low boiling point will almost always carry with it a high vapor pressure meaning that our liquid will readily convert to a vapor, which, as we established, is the most difficult to control. Now let’s examine Chlorine. It has a boiling point of minus 30 degrees Fahrenheit and a vapor pressure of 7600 mm Hg. This means that Chlorine always wants to be a gas.  If we put it in a container and raise the pressure, it forces some of the gas back into a liquid. This allows us to transport more of the material and makes it easier to transfer. Everything is copasetic until we puncture the container.  Think of a pressure cooker, pressure is applied to water, which raises the boiling point, allowing the water to reach temperatures higher than 212 degrees Fahrenheit before boiling (turning to gas). As soon as the liquid escapes its high-pressure environment, be it a pressure cooker or chlorine cylinder, it is exposed to atmospheric pressure and becomes a gas again.

If we have identified that our liquid will readily vaporize, we want to know how much of the vapor we will have to deal with in relation to the liquid. This can be found in the vapor expansion ratio portion of our research materials. Remember the vapor expansion ratio of water?  It is 1700:1. For every one part of water, we will have 1700 parts of steam (vapor) produced once it is heated to its boiling point. Chlorine’s vapor expansion ratio is 450-500:1. So, we hope to see low vapor expansion ratios because high vapor expansion ratios means we have more material to deal with once it converts from liquid to gas.

Hazardous materials response continues to be one of the most technical forms of the modern day fire service. If you take the task oriented hands-on stuff associated with fire suppression, along with the investigative techniques and inductive reasoning we use in investigations, add a sprinkle of emergency medicine, along with the chemistry classes we all now wish we didn’t sleep through in high school, then you have modern day haz mat responses. Another one of Alan V. Brunacini’s timeless truths is: “It’s very painful to be challenged and lonely at the same time.” Remember that no fire department can handle a major haz mat call alone, don’t be afraid to “phone a friend” or more. Continue to review your research material terms, the operation of your air monitors and detection equipment, and review how chemicals hurt people, and you will be well prepared when that pop rivet hits your department in the forehead.

Be safe and do good.