Search Past Articles
Explore Past Articles
Haz Mat "Specialist Course"

Vapor Density and Specific Gravity

Vapor Density and Specific Gravity are integral concepts that can tell you where your hazardous spill or release will go. If you understand how these relate to your product you can accurately predict and anticipate needed changes to your scene before citizens or responders become exposed. This of course, minimizes injury and contamination. Both vapor density and specific gravity are based on an arbitrary scale surrounding both sides of the numeral 1. Vapor Density measures the weight of a gas or vapor in air, using 1 as the weight of normal outside air. Specific gravity measures the weight of a liquid or solid in water, using 1 as the weight of normal water.

Vapor Density using this scale gives us immediate information allowing us to formulate our future plume dispersion plans. If the vapor density is determined from chemical information resources to be less than 1 a number of constants can be calculated. For most vapors lighter than air, the tendency upon release, {In addition to rising in the sky} is to dissipate and become weaker very fast. This is beneficial for a number of reasons.

  1. Evacuation is non-existent or confined to the immediate area.
  2. Exposure to un-protected persons is usually minor.
  3. Day-to-Day operations are minimally disrupted.
  4. Mitigation equipment of the released vapor is natural dispersion.

All four of these response issues decrease the drain on your man-power and equipment. Generally the contamination area is small and can be dealt with by few responders. Since confinement is impossible, and containment depends on the vessel releasing the vapor plume, tactics should involve the use of an air monitoring device. Once the plume direction has been evaluated it is critical to determine the location of the PEL {Permissible Exposure Limit} on the downwind side affecting civilians. Beyond this position evacuation is not necessary and harm to the public will be limited to an unpleasant irritating odor. By placing one firefighter at this point to prevent civilians from entering any area above the PEL, you have isolated the area of contamination from the public. This is one reason why chemical facilities are usually found with large area sites. If a plume dispersion scenario occurs, their fenced in grounds may be large enough for this to occur. In this case, their fence eliminates the need to post a firefighter or employee at the PEL limit downwind.

If the Vapor Density of the release is greater than 1, other issues are presented. Entrapment in confined areas by vapors, asphyxiation, and unstable air currents, are just some of the concerns. As you can see by the drawings, heavier than air vapors will fall near the ground right where we humans breathe. If they fall into a sub-level area we may be asphyxiated. Generally, these heavier than air vapors with a vapor density greater than 1 tend to stay concentrated for a longer time. As a result, they are more hazardous remaining above their PEL, and from the physics of being denser than air. Since there are uneven air currents near the ground surface, these toxic vapors can travel quite far and still remain above the PEL. If they are flammable, they can re-surface inside a building through basement drains, possibly finding an ignition source, such as the water heater or furnace creating explosion possibilities. Because of these properties, a response to a scene involving a vapor release greater than 1 will require more man-power and equipment. If in an industrial area, streets will need to be roped off. If in a residential area, door-to-door warnings may have to be implemented. These actions will all require a larger commitment from your department.

Specific Gravity involves the same type of arbitrary scale of 1, except now we are evaluating the weight of a material when mixed in any form of water. Sewer drains, lakes, oceans, etc, if the information resources data reveal a number less than 1, the material will float on top of water, much like gasoline in a puddle does. If the data reveals a value above 1, it will sink as in the example of Carbon Disulfide. Since most contaminants spilled have a specific gravity less than 1, you will find much re-mediation equipment and data for these types of spills. Booms, Vactors, Absorbent Pads are among some. The general format for these spills is the area is larger but the contaminant is easier to pick-up and retain. It does however require vast equipment and man-power for open water, less than 1 specific gravity, spilled contaminant. Defining “easier” becomes the issue. For spills with a specific gravity above 1, which sink to the bottom of a waterway you will not find much remediation data or equipment. These types of spills are less frequent and very expensive to mitigate the bottom of a waterway. The three most common treatments for this type of spill are:

  1. Natural environment absorption, which sometimes works and sometimes ruins a waterway.
  2. Specialized dive teams with imbibed absorption capabilities.
  3. Overall reduction of these chemicals uses, by switching to a non-hazardous alternative.

This concept is quickly becoming the industry standard for many hazardous chemicals. Ultimately, while this is best for people and the environment it may also eliminate the need for us Haz-Mat guys.

Haz Mat Mike


Monomers Into Polymers

     Monomers can be thought of as the constituents of polymers. What this statement refers to is how these molecular units are related to each other, rather than their pure chemical make-up. When monomers form polymers they do change into a new compound with its own set of unique chemical properties. This change is what gives polymers their vast use in industry and in many common place materials that can save us time and maintenance in our daily lives.
     Monomers can be thought of as a bag of individual chain links all floating separate next to each other, but not connected. In the monomer state they remain this way, through the application of an “Inhibitor”. An inhibitor is essentially the reverse of a catalyst. The inhibitor PREVENTS a reaction from taking place. For emergency response, the inhibitor has its challenges. Inhibitors are time dependent as to how long they will continue to be effective, or prevent a reaction. Inhibitors are also affected by sunlight and exterior temperature. If the time lapses longer than the effective rate of the inhibitors life or exterior temperatures increase or the monomer becomes exposed to sunlight, polymerization can occur. This is exactly what has happened in these photographs.
     When polymerization occurs, all the floating chain links combine together to form one long chain, quickly! When this occurs in an industrial process reactor, the result is a new desired product which can then be formed into all manner of things we use in our daily lives. However, if it occurs outside of this reactor process, such as in a transportation vehicle involved in an accident three things are likely to occur:

  1. Tremendous heat is evolved by the polymerization process.
  2. Rapid expansion occurs.
  3. Violent shaking of the vessel containing the monomers evolves.

    All three of these challenges can injure emergency responders in close proximity of a container with a failed inhibitor. Extra heat can burn responders or hinder firefighting operations. Rapid expansion can overflow into other areas making the environmental spill worse or cause an explosion of the vessel injuring responders from blast and container shrapnel. Violent shaking of a container can disconnect one vessel from another causing more contamination or physical injury to workers or responders.
     The greatest hazard for responders when dealing with monomers is the potential for polymerization and detonation. The main challenge will be to determine the length of time you have until the inhibitor wears out. After that, detonation can be imminent. As you can see by these photographs, this turned out to be a slow leak of the polymer transformation yielding the traditional “Green Goo” we Haz-Mat people are known for. Can you imagine the injury and damage potential if this 55 gallon had detonated? Respect polymerization potential, especially if it’s next to 1075!

Haz-Mat Mike


Cool Environmental Solution

     I believe as hazardous materials responders we are always part of the solution. Whether the response is environmental, fire, or EMS, we are always improvising solutions to our immediate problems in order to save lives. While National Foam responds to fire or hazardous materials vapor suppression incidents, they too improvise solutions to save lives. Whether it is with an impressive array of Foam solutions, portable equipment or stationary fixed systems, now they can tackle the environment. While this solution may not be Haz Mat response, it’s just plain cool.
     Several years ago, ACT Inc., specializing in lake restoration purchased a portable eductor for a unique device they were developing. Their machine was designed to apply environmentally sound chemicals to the lake bottoms containing an overabundance of weeds or algae. The chemicals involved, when mixed together, formed a “flock” which settled on the lake bed, inhibiting the germination and growth of nuisance vegetation.
     Only one problem, the application of these chemicals had to be mixed under water to be effective. ACT’s concept was to construct a floating platform with the device mounted underneath. It consisted of two, above deck mounted feeder {distribution} pipes, one for each chemical, and one mixing pipe. The two chemicals were applied by small spray nozzles inside the mixing pipe. As the sprays mixed, the “flock” was created and settled to the lake bottom.
     When ACT designed the original device, they contacted National Foam for an effective proportioning unit for this system. The end result was an eduction device that proportioned the chemicals from drums on the floating platform and carried them in the proper quantities into the two feeder pipes.
     After this success, ACT ordered a second eductor for yet another application device. So, while nuisance lake vegetation continues to threaten our lakes, National Foam continues to respond to our environment. See, I told you it was cool.

Haz Mat Mike


Clandestine Methamphetamine Drug Lab Scenario

The photograph set for this article is representative of an actual field exercise for training responders that are expected to successfully mitigate a Clandestine Drug Lab. This scenario was devised for our responders at a recent Homeland Security Training Conference. Your Teams’ response may be different, but all teams must follow the following format to efficiently succeed in any type of response.

  1. Responsible staff members must determine the “level of response” your group will offer BEFORE you respond. All Haz-Mat incidents have varying levels of response service. Are you going to rescue victims? Are you going to stop leaks and or releases? Will you do both? Are you going to over-pack damaged containers? Are you going to mitigate the environmental area and impact back to the level of operation before the incident occurred? Inside all of these choices are also many “levels of response” that must be determined before responding begins so that all involved understand what they will get when they call you! This facilitates a smooth response, and that all the needed groups to control an incident are called early.
  2. ID {Identification of the chemicals involved} the products before operations begin. This may very well require a properly suited entry team to ID the products involved. This is all well and fine, just remember until these hazards are discussed among your response group, no mitigation should occur. In some cases VERY simple mitigation operations can be done by the initial entry team sent in for ID, but this must be pre-agreed by all members of your group, and depend on the severity of the hazards involved. This technique is called prioritization.
  3. Prioritization of all hazards before operations begin is paramount for overall safety. Simply put, you must discover which hazards are the most dangerous at the site. The steps for prioritization in this order are: 1] Decide what hazards are the most dangerous to you. 2] Rank them in order of severity and mitigate them in that order, the most dangerous first, the second, one step less hazardous than the first, and so on. 3] Determine which possible mixtures of the “free” hazards involved could become explosive, or more toxic than the first hazard you chose if mixed together. Once this has been decided you can begin to suit up the next volley of responders to handle these hazards in the order you have agreed upon.
  4. Mitigation requires many skills based upon what type of hazard and container you are dealing with. One important operation that often goes undone is that of separation and isolation. First, always remove the intact, uninvolved containers away from the hazard area if they are of a movable size by one or two responders. This simple act will minimize the severity of reaction or explosion if the incident deteriorates while you are in the “Hot-Zone”. This simple operation, when done, has saved many responders lives.
  5. Environmental return to “normal business” refers to the actual site being clean enough for normal workers to return to the site, in their normal work attire. If your Company is Environmental in nature, this may be the largest part of the work performed before you finish the job and “clear the site”. Most response teams of an Emergency nature do not have the training, manpower, or equipment, for an operation of this magnitude. Only Environmental Contractors have heavy moving equipment, transportation licenses, hazardous waste receiving sites, or recycling centers all aligned and ready to handle shipments of hazardous waste. Be advised, that at some point in the incident you will be working with these people, so call them early to your scene.

In this event, we had students follow these rules and implemented a color coding system for environmental monitoring results. This was done to keep the site clean, as the training norm is to never have “live chemicals on site”. By instructing the students during the “Prioritization” section of the exercise, I assigned each hazard found, a color of its container indicating what the monitoring results would be if these chemicals were on our site. This worked well with the separation and isolation aspect of the exercise, as long as they did not rely on the containers labels. Can you see if any mistakes were made?

Haz-Mat Mike


National Foam

Pictures accompanying this article can be found right here, and always check out the "Pictures from the Field" link up top when a new article is posted, there will usually be a corresponding picture set.

     One of the most under used and under appreciated tools for hazardous materials mitigation work is FOAM. One of the best products I have used is from the company called National Foam. I had the distinct pleasure of attending their class and becoming a National Foam Industrial Instructor many years ago. These people specialize in FOAM and all things connected to firefighting foam. They are staffed by area firefighters which makes them the horses’ mouth as far as interfacing with all fire departments. With this type of liaison, whenever you have a question regarding the implications of their product, you never have to deal with a salesman. You are dealing with a fireman. This prevents miscommunication and gets you the customer the correct answer the first time. National Foam has received awards from the federal government regarding all the saved lives it was responsible for aboard Navy ships during WWII. In addition, all appliances for National Foam are fabricated on site by many of these same firefighters. National Foam also builds Foam Firefighting apparatus for Oil field firefighters around the globe. This is definitely a top drawer organization. One particular product I am very fond of is “Universal Gold”.

     In the beginning days of hazardous materials vapor suppression, Foam for haz-mat use was a sloppy affair, had clogging issues in the field and generally was so difficult to use that it was placed on the back shelf of most firefighting operations. With the domestic increase in terrorist activities in our country vapor suppression has risen into high concern within our list of needs. Vapor suppression of any contaminant released by accident or on purpose accomplishes two goals for the firefighter:

  1. By stopping the evolution of vapors from a release, large scale evacuation procedures along with non-existent man-power to carry out those procedures is not needed. Think of your department and just imagine the amount of planning, man-power and equipment that you would need just to evacuate one senior citizen home in your town. “It isn’t going to happen” we do not like to hear this, but we all know this is the truth. In place sheltering is fine, as long as those senior citizen buildings can be self-sufficient and sealed from the outside for an extended time period. Most will never be, and are not now. Complete and rapid vapor suppression of an area spill or deliberate release completely eliminates exposure to nearby citizens.

  2. Confinement of these vapors along with product confinement gives the fire department command time to adapt. Very few of us have resources immediately at our disposal. By having the time to deploy these contractor resources we can save lives.

     National Foam replaced the difficult challenges of early “mixed foam” with Universal Gold. The stats on this particular product are stunning. As you will see in the following photographs, Environmental usage is as impressive as its vapor suppression capabilities. For any of your Foam needs, contact these people. There are many issues regarding Foam and its’ use, but in firefighting mode I have found the greatest challenge to be application. There are three main areas that are critical for a successful outcome:

  1. volume onsite
  2. air aspiration
  3. application rate

These three are the most important if you want to save lives and minimize destruction at your site.


     Due to the concept of “¼ drain time” you must be able to calculate the total gallons of Foam you will need, and have it onsite before Foam application operations begin. This is due to the “1/4 drain time” concept of the Foam bubble breaking down and returning to its liquid form. If you cannot replace and increase Finished Foam faster than it drains, you will not be able suppress the fire vapors. The result will be that the Foam “burns back” faster than you can apply it and cool or smother the surface, resulting in a continuation of the fire, or continuation of vaporization of hazardous air pollutants.

     To get the best performance out of your Foam, ALL nozzles must be air aspirating. The aspiration of air into the Foam solution directed from your hand-line is what produces finished Foam of the highest quality. If you view the Tanker Fire on I-75 in Hazel Park, Michigan on July 15th, {of which I will have pictures and video up soon} this is exactly why I remained on this scene from 2022 until 0330 the next morning. We had major problems delivering this volume of Foam.

     The application rate is another critical factor that must be taken into consideration. Unless you can deliver the volume of Foam required for the size area of the fire, at the proper speed, you will revert to the same end as the “1/4 drain time” scenario. The Foam applied will not be able to overtake the burning rate and extinguishment will be unsuccessful. In your operations, be sure you can implement these three concepts before attacking a flammable liquid fire. The accompanying photos from National Foams Training Program highlight these concepts and other interesting points.

Haz-Mat Mike