Archive for June, 2015

by: Jason A. Sutula

Most people do not think about metals burning when they think about combustion and fire. Yet, metals can combust, especially when the metals are being used within an industrial process or themselves being processed at higher temperatures. Fortunately for the process safety, mining, and other industries, much research on metal combustion has been done over the years. One of the first studies on the burning of metal dusts was published in 1955 by Titman (Titman, 1955).

Titman examined small metal particles and the influence they had on the explosive mixtures of gases. Additionally, the metal dusts themselves were determined to have explosive properties. The hazards of metal dust combustion are similar in nature to those of organic dusts, which were discussed in a previous post of mine (The Creamer Canon). Since metals have a high affinity for oxygen and have the material property of high heats of oxidation, they are capable of producing high temperatures and the liberation of energy in very rapid fashion.

Another seminal, systematic study was conducted by Harrison and Yoffe in 1961 and published in the Proceedings of the Royal Society of London (Harrison and Yoffe, 1961). Harrison and Yoffe conducted their experiments using wires of various metals. These metals included aluminum, iron, magnesium, molybdenum, titanium, and zirconium.

Harrison and Yoffe demonstrated that the process of metal combustion was much more difficult to initiate when the metal was in wire form as opposed to dust. Their results indicated that the explosive hazard associated with the metal dusts were not as much of a concern with larger chunks of metal. Additionally, Harrison and Yoffe discovered that the mode of burning for each metal was determined by the relative melting and boiling points of the metal and the metal oxides (which is formed as the product of the combustion reaction).

Today’s embedded YouTube video selection demonstrates the energetic reaction produced by titanium powder burning. The reaction of the individuals involved is eerily similar to that of the Mythbusters crew as seen in the Creamer Canon video. In addition to providing a means to educate us through videos on the internet, combustible metals do have many other useful purposes. One such is the use of metal dusts to ensure a specific color in commercial firework displays. Titanium, Aluminum, and Magnesium powders are used to make a vibrant white color in the pyrotechnic stars. With that in mind, an argument can be made that the Chinese were actually the first researchers who began walking the path of understanding metal combustion. Have a happy and fire safe 4th of July!

Titman, H., Trans. Inst. Min. Engrs., Lond., 115, 1955.

Harrison, P.L., and Yoffe, A.D., “The Burning of Metals,” Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, Vol. 261, No. 1306, pp. 357-370, 1961.

by: Raquel Hakes

Wildfires. I want you to stop and think a moment. When I say that word – wildfires – what comes to mind? Maybe if you live in the United States, you think of the West. Maybe the word “wildfires” is synonymous with California or Arizona or Colorado. Maybe you are from Australia and mentally translate “wildfire” to “bushfire.” Perhaps you have watched news stories covering major fires or you took your kids to see the Planes: Fire & Rescue movie and that is really your only familiarity with the idea of wildfires.

I have lived in the East for over a decade and a half now, but I still go back to Arizona to visit my father’s family. They live far down south, close to the border with Mexico, near a mountain range. One year, I arrived, and the mountains were black. Everything along the side of the roads was black. I had followed the news on the wildfire closely from across the country, but seeing the devastation first hand was another matter. The Mexican restaurant that had stood a few miles down the road from my cousin’s house for several decades was gone. They planned to rebuild, but never managed it. We woke up to go hiking one morning, but the park we wanted to visit was closed. There was too much damage; downed trees, burned vegetation, blocked roads, and erosion. My cousin’s house was safe, but when I left, I could not help but wonder if the house would still be standing if the fire had been closer.

Even something as relatively small as a house fire probably seems far from manageable. You have your smoke alarms and maybe sprinklers. You try to clear paper away from your fireplace. You hope you remember to turn off the stove when you leave the house, and you extinguish your candles before going to bed. There are little things you can do, but once a fire starts, the task of extinguishing it can be overwhelming and most likely impossible for you. You have to leave it up to the firefighters and hope.

What about when a fire is so much bigger? What about when the forest or grassland around your house is on fire? Or you go to sleep, and it looks like the mountains are burning? And what if none of this has happened to you yet? Maybe you know that it is possible – not just out West, but many places – for a wildfire to occur.

Many people are not sure what to do if they live in a place with wildfires (for those in the U.S., these places do include Maryland, Florida, Massachusetts… it is not just the West). Perhaps they do not know the risk or, if they do, they do not know what effect their actions could have. If that is you and you are wondering, I have some good news: there are things you can do to keep your house safer, all of which are easily manageable.

Here 6 ways you can prepare for a wildfire:

  1. Find out your risk– This is a combination of how often wildfires occur in your area, how severe they can be, and how protected your house is or is not.
  2. Clean your gutters– This is a major way fires can start at your house from a wildfire! Firebrands, basically embers or coals, can fly out from the fire and land in your gutter or other places around your house. If you have a bunch of stuff in your gutter, it might catch fire and spread to the rest of your house.
  3. Rake your leaves– This follows along from point #2. Move the dry leaves (very flammable) away from your house. Even if you only rake them a few feet away, this can make a huge difference.
  4. Do not put your woodpile (or mulch pile) right next to your house or under your deck– Imagine the biggest bonfire you have been to. Would you want that next to your house? Probably not, so move it out further in your yard or into your shed.
  5. Plant smart– Some plants are more flammable than others. For example, plants that produce a lot of dead branches can catch on fire more easily. Junipers, hollies, and other coniferous plants are fairly flammable. Plant things that will not burn as easily, such as deciduous plants. If you are not sure what plants burn, a quick internet search gives a myriad of helpful results.
  6. Educate yourself– There are tons of resources out there for you, put out by the NFPA, Ready, Set, Go!, local fire departments, departments of natural resources, and more. Start looking and keep yourself safe!

What does the word “wildfire” mean to you? Maybe it still means a faraway place and maybe it means close to home. Maybe it reminds you of friends or family that have experienced a wildfire. Whatever the answer is, I hope you now understand that you have some control over what happens if a wildfire ever becomes more personal. A few little actions will go a long way to keeping your home safe from a wildfire. Wishing you good weather for raking and cleaning!

by: Jason A. Sutula

This past Friday, Sara Caton presented an excellent take on the potential electrocution risk to fire service personnel when encountering a roof-mounted solar array during an active fire event. Her post raises several good points that must be accounted for in both the training of firefighting personnel as well as understanding the interaction between a solar panel installation and the building construction elements below it.

As a follow up to her post, I received a comment from Professor James (Jim) Milke, Chair of the Department of Fire Protection Engineering at the University of Maryland. Professor Milke reminded me that Rosalie Wills led a group of students that put together a report for the Fire Protection Research Foundation (FPRF) on the hazard assessment of commercial installations of roof-mounted solar panels. The report highlighted a range of environmental exposures in addition to the more common discussion of the performance of the array when involved in fire.

Structural loading, wind loading, hail, snow, debris accumulation, seismic activity, and the hazards of fire are all addressed within the report. A common theme among many of the hazards that were assessed was the idea that the weight of the solar array is not negligible. A photovoltaic array is commonly mounted on to a typical roof assembly that was not originally designed to account for the additional loading of the array. While the roof assembly can support the loading of the array in normal conditions, wind loading, snow loading, and loading from other debris accumulation can cause stresses within the roof assembly over time.

When fire is added to the equation, the increased structural loading on the roof assembly can cause more rapid failure and collapse, especially if an interior fire exposes the roof members directly below the area where the solar array is mounted. Destruction of the supporting building construction under the solar array will cause damage to the electrical distribution system from the array to the structure leading to the development of the electrical hazards to firefighters as discussed in the previous post.

The model building codes have developed new provisions that address some of the hazards analyzed in the FPRF report. The 2012 edition of the International Building Code (IBC) requires a solar array system to have the same fire class rating as the roof assembly. Additionally, Underwriters Laboratory (UL) Standard 1703 (Standard for Flat-Plate Photovoltaic Modules and Panels) was updated with additional testing methods to be able to account for a roof mounted photovoltaic fire class assembly rating. Finally, NFPA 70, the National Electric Code (NEC), has included many provisions within the latest edition to limit the potential of an electrical failure of a photovoltaic system. Progress in the fire safety and minimization of the hazards of these systems continues to be made.

If interested in more information, take the time to watch today’s embedded YouTube video. This was created by the NFPA, and Ken Willette does a good job of pointing out the resources available for fire safe installations of photovoltaic systems.

by: Sara Caton

Sustainability, green technology, and clean energy are all trends that are found at the forefront of engineering and design in today’s world. Because of society’s focus on sustainability, photovoltaic (PV) panels, which use sunlight to generate electricity, are increasingly popular renewable energy systems. In 2013, PV installations in the twenty-four countries that make up the International Energy Agency (IEA) Photovoltaic Power Systems (PVPS) Program combined with non-IEA PVPS countries totaled approximately thirty-nine to forty gigawatts. This total is the highest installation value ever for PV, with a growth of about 35%. (Photovoltaic Power Systems Program, 2014) Although the installation of PV systems increased in 2013, the total investments in renewable energy actually decreased. This can be attributed to the cost reductions of solar PV installations. (Global Trends in Renewable Energy Investment, 2014) The IEA PVPS Program findings and the decreased installation costs emphasize that the use of PV panel systems is a global trend that will continue to grow.

I am completely on board with these PV installation trends, because I believe it is an easy way for people to incorporate the use of solar energy in their lives. PV systems provide great benefits to the environment, which is why the installation of them is so popular; however, these systems can pose great dangers and threats, especially during a fire event. A building that has a PV system installed on the roof may experience increased building loss during a fire compared to a building without a PV system, and the emergency responders are faced with new and different dangers during a structure fire that has a PV panel system. These are concerns that fire protection engineers need to be aware of in order to better protect buildings and people from fires that involve buildings with PV installations.

Lessons can be learned from fire incidents that involve PV panel systems. A fire occurred in a chemical manufacturing facility in West Berlin, NJ that, according to officials, was caused by propane tanks igniting and causing multiple small explosions inside the facility. (Glover, 2014) Dozens of rows of PV panels were installed on the roof of the building, making matters worse. When water was sprayed onto the roof from above, it collapsed. “Firefighters were forced to knock down an outer wall of the facility to expose the collapsed solar panels as well as to fight flare-ups.” (Glover, 2014)

From this example, it is illustrated that building loss and damages can be severely increased during a fire in a structure that has a PV system installed on the roof. The PV system adds a dead load to the roof and can be affected by other external loads caused by the elements. These added loads could be part of the reason the roof was not able to withstand the water jets. Since the PV panels posed an electrocution threat to the firefighters, they had to find alternative options to approaching the fire, which resulted in this example by taking down an exterior wall. This action also increased the amount of damage to the building.

I think it is important to investigate and ask questions about fire incidents that involve PV panel systems to learn how to avoid these dangerous fires and how to protect the emergency responders from these new threats. The two main dangers that these fire pose to emergency responders are electric shock due to direct contact with energized components and electric shock from water-based fire suppression. If energized components are exposed because the protective covering of the panels break due to the fire or fire fighting techniques, the fire fighter can receive an electric shock from direct contact. Because it is impossible to fully de-energize the components of the PV systems and water is conductive, using water for suppression without the threat of electric shock becomes difficult.

There has been research done that suggests safe distances for water application and nozzle spray types, appropriate insulated gloves for firefighters, and the use of tarps to help de-energize PV components. In my personal opinion, more research needs to be done to develop adequately safe fire boots that will help the firefighters avoid electric shock. The table below shows that tests conducted at UL found that aged boots do not perform well in response to shock. Firefighters’ boots generally have conductive metal toe and sole plates to protect the foot, but this conductivity can be a danger when dealing with energized electrical components (Backstrom, 2011). In order to not negate the benefits PV systems provide for the environment, it is vital for fire protection engineers to ensure the safety of firefighters who may be faced with fighting PV system fire incidents.

References

Backstrom, 2011: Robert Backstrom and David Dini, Fire fighter Safety and Photovoltaic Installations Research Project, Underwriters Laboratories, Inc., November 29.

Global Trends in Renewable Energy Investment, 2014: Global Trends in Renewable Energy Investment, Frankfurt School of Finance and Management, 2014.

Glover, 2014: Sarah Glover and Vince Lattanzio, “Fire Destroys NJ Chemical Manufacturer’s Facility,” NBC News, May, 2014.

Photovoltaic Power Systems Program, 2014: Photovoltaic Power Systems Program, “Trends in Photovoltaic Application 2014,” International Energy Agency, 2014.

by: Jason A. Sutula

Last week, Peter Raia discussed the need for research into the fire dynamics behind the penciling and full-flow techniques for fighting a compartment fire. The timing of his article fits nicely with the proposed development of a new standard on the fire control of structures based upon fire dynamics.

At an April 2015 meeting, the Standards Council of the National Fire Protection Association (NFPA) considered the request of Richard Dyer of Kansas City, Missouri on this particular topic. The council voted to solicit public comments and expertise to sit on a new technical committee on the Fundamentals of Fire Control Within a Structure Utilizing Fire Dynamics. Additionally, a page was developed to facilitate public comments and applications for the technical committee (http://www.nfpa.org/structurefirecontrol).

The scope for the new project is extremely pertinent to Mr. Raia’s discussion on using science and research to better understand the most efficient way to extinguish structural fires. According to the justification at the NFPA, the new document will be designed to assist government, military, and private industry fire fighters in developing recommended procedures, strategy, and tactics for combating fires in all types of structures. Even more importantly, the long term goal will be for a unification of standard operating procedures at fire departments throughout the United States.

Daniel Gorham, Associate Engineer with the NFPA, is helping to drive interest in the new standard. Please take the time to click on the above link to the main page for the proposed project. The public comments close today, so if you are interested in putting in public input, you will need to get those in before the end of the day. Technical committee applications will be accepted through July 22, 2015.

Finally, for those of you who may be wondering about why this proposed standard and further research is necessary, please take a look at the embedded YouTube video. This was shot and posted by Anthony Bendele of Truck 542 from Sunbury, Pennsylvania. It is a helmet cam video of the everyday fight our fire service personnel experience. Protecting our most valuable asset in the fire service, the men and women who serve, will always be a noble goal.

by: Peter Raia

The fire service is a traditional, paramilitary brotherhood that is one of the most long standing professions in the world. I had the privilege of joining this brotherhood in 2007, at the age of 15. I quickly gained a large interest in firefighting and wanted to learn what goes on “behind the flame,” for a lack of a better phrase. Shortly after joining the fire service, I stumbled upon the Fire Protection Engineering Program at the University of Maryland and gained an entry level understanding of fire dynamics and computer fire modeling. Unfortunately, some of what I learned with my degree did not correspond to my knowledge of basic firefighting.

“Penciling” is a technique taught in fire academy classes as, “short blasts of water, aimed at the ceiling, to provide enough cooling to stop or slow a flashover.” I was taught that three, one second long bursts at the ceiling are enough to cool the ceiling temperatures to fight back the onset of flashover and allow the fire attack crew to push on to the seat of the fire for final extinguishment.

As a fire protection engineer, this practice did not make sense. Why would you only provide three short bursts of water at the ceiling when you have a “relatively infinite” amount of water to cool the surrounding atmosphere? And, why just at the ceiling? The ceiling only accounts for one of the sides of the room that are affected by the high temperatures of the upper smoke layer. The temperature of these surfaces can be near, and sometimes over, 1000 degrees Fahrenheit immediately before flashover. Three short shots of water at the ceiling will only decrease the temperature slightly and for a short amount of time before the upper smoke layer overwhelms the cooling and heat displacement created from the water application. In my mind, it made more sense to apply water to multiple sides of the compartment, hopefully causing a rapid decrease in the compartment temperature and the conversion of liquid water to steam.

I took this question to my fire academy instructor, who I am very friendly with and currently work alongside with as a firefighter. The response I received was not as grounded in science as I expected. My friend stated, “Pete, that amount of water would cause extreme steam burns to your body (i.e., rapid steam expansion due to the water phase change), and it is the way it has always been taught.”

I partially agreed with his first point. Steam burns are atrocious. They resemble and feel like severe sunburns, but occur all over the body in some cases. However, these burns have become rarer with improvements in protective gear standards and new and improved practices in fire ground ventilation.

His second argument was more problematic. The standard rebuttal, “because that’s the way it has always been done…,” is just not in line with modern fire dynamics and fire fighting tactics. This answer simply is not good enough to warrant the practice of a technique that is performed in as hazardous a job as fighting fire.

With the help of online resources, I began to research the direct application of a continuous water stream to the upper layer in an effort to rapidly cool and decrease the flashover temperature of the fire room. Kill the Flashover is one example of a group that is working on this type of research (NIST has also conducted research in this area). As a group of firefighters/engineers, they are dedicated to examining the ins and outs of attacking and preventing flashover. In addition to many other live fire burns, they have performed a comparison test of the penciling technique and the full-flow technique. In their experiment, Penciling demonstrated improvement in the fire compartment, but these improvements were temporary and still fostered high temperatures and dangerous operating conditions for the interior firefighting crews. The full-flow technique performed much more consistently, and in some instances resulted in the full extinguishment of the fire in the compartment.

A question to now pose to ourselves is, “do we get firefighters to use this method?” More research is certainly needed, and once completed and analyzed, the next step is to get this information out to the fire service community. In my experience on the fire ground, practice is the best form of education. The more you practice a proven technique, the more convinced you will be of its validity. In modern firefighting practice, it is imperative to question the old “because that is how it has always been done” attitude and embrace the idea of more adaptive and scientifically-based techniques.

by: Jason A. Sutula

In a previous post on the topic of fire in space, I discussed the 1997 fire incident aboard the Mir Space Station. The case study still resonates today and provides valuable lessons for both NASA and the private commercial space companies on what fire hazards can be expected and need to be defended against in both manned and unmanned spacecraft missions. The single most important lesson that the Mir incident taught us is that the process of a fire burning in space is not intuitive.

Gravity, the driving force for natural fluid flow on the earth, cannot exert its influence on people, objects, and even fire when they are in a spacecraft circling the globe. In free fall around the plant earth, hot gases do not rise, and cold gases do not fall. The effects of buoyancy as seen in earth-bound fires are removed, which results in drastic differences in the appearance and structure of flames.

Fortunately, research in these areas has continued over the past few decades. Several on-going research studies are currently being conducted independently as well as in conjunction with NASA and the International Space Station in efforts to more fundamentally understand the fire hazards in microgravity environments.

One study by McGrattan, Kashiwagi, Baum, and Olson (McGrattan et al., 1996) demonstrated some strange fire behavior in microgravity conditions. For the study, a thin cellulosic fuel was suspended in a combustion test rig designed for a 2.2 second drop tower. The 2.2 second drop tower provided of a short amount of simulated microgravity conditions while the fire was burning. Ignition occurred in the middle of the sample and the flame was allowed to spread both vertically “upward” and “downward” at the same time. As a further variable, the researchers forced an air flow across the fuel sample at various speeds. The results were very surprising. The researchers initially expected the flame to propagate more rapidly in the downstream direction of the flow of air (think of how a camp fire will flare up when you blow on the coals). Instead, the fire burned more readily in the upstream or “opposed” direction of the flow, and the downstream flame died out quickly.

McGrattan et al. formulated a two-dimensional, time-dependent combustion model using computational fluid dynamics to better understand the phenomenon. Their computational study demonstrated that the flame moving in the opposite direction to the flow created an “oxygen shadow” in relation to the flame moving in the same direction as the air flow. This resulted in the downstream flame extinguishing since the flame moving toward the flow had already consumed all of the available oxygen!

In the embedded YouTube video above, Dr. Sandra Olson of the NASA Glenn Research Center, presents actual footage of the flame front burning as it is dropped in the 2.2 second drop tower. The full video is geared toward a younger, more kid friendly audience, so if you want to skip ahead, the microgravity combustion video and discussion begins at 0:51.

More research and computational studies will need to be conducted by NASA and commercial space ventures to better understand all of the fire hazard risks associated with microgravity environments. Fortunately, there are pioneers in this field laying the groundwork for fire safety in the final frontier.

McGrattan, K.B., Kashiwagi, T., Baum. H.R., and Olson, S.L., “Effects of Ignition and Wind on the Transition to Flame Spread in a Microgravity Environment,” Combustion and Flame, 106: pp 377-391, 1996.