For those of you who have not experienced live fire-training exercises, we will take a moment to summarize operations ongoing in a burn building. Burn buildings are generally concrete or steel structures in which firefighters arrange fuels to be ignited and extinguished for training exercises. These fuels are usually “Class A” (wood, straw and paper products). Certain newer facilities contain controlled propane or natural gas burners and steel live fire training props to simulate uncontrolled fires. During a normal training day, firefighters may ignite and extinguish these fuels many times. One ignition and extinguishment of a fire is called an “evolution”. Three or four evolutions per hour during the course of the training session are normal. The session may last four hours for one department. It is not unusual for several departments to use the same structure in one day. Therefore, a structure could see thirty to fifty evolutions during a busy day. A certain amount of heat soaks into the structure when an evolution is conducted. A little more heat sink is generated with each evolution. By the end of the day the building is saturated with heat and will take a full day to cool off. The building may not have a chance to fully cool if fire stimulation training is ongoing the next day. Many fire departments use live fire training props for their training as well.  
 
The size of the room, the size of the fuel loading and the average duration and number of evolutions will all affect the temperatures generated in the building. A typical "Class A" loading, including a bale of hay and two to four wooden pallets, will develop temperatures of about 200 degrees Fahrenheit near the floor and about 900 to 1100 degrees near the ceiling. It is not uncommon to experience ceiling temperatures between 1300 to 1700 degrees. Once the fire is allowed to fully develop, firefighters extinguish the fire using pressurized water delivered with fire hoses. Fire hose are capable of delivering hundreds of gallons of water per minute at pressures of generally 50 to 100 pounds per inch. Some of the water immediately converts to steam, expanding 1700 hundred times its' volume. This pressure plays havoc with the firefighters and the building. In addition to steam and the effects thereof, the building is subjected to its' worst enemy ~ thermal shock. What is thermal shock? Have you ever taken a hot glass from the dishwasher and immediately placed it under a cold stream of water? What happened? The glass will often shatter.
 
That phenomenon is called thermal shock. When a material is heated or cooled to extreme temperatures, and then suddenly subjected to oppositely extreme temperatures the material tries to react by expanding or contracting. The characteristics of the material may not allow it to adjust so quickly. When this happens, the binding element within the material fails. Such failures often show up as simple cracks; such as in structural concrete ceiling or floor slabs. Occasionally the reaction is more violent, as with concrete explosions. Concrete can actually explode like a hand grenade if water inside the concrete turns to steam and is unable to escape. The pressure developed by the steam is greater than the tensile strength of the concrete. When this happens, chunks of concrete and stone are blasted into the room with extraordinary force. More frequently however, the concrete has cracked over time and steam escapes through those cracks. Eventually, however, reinforcing within the concrete corrodes and large slabs of concrete fall away from the ceiling or walls. These are called spalls. Spalls result in weakened concrete sections.
 
When a slab begins to spall, it is a clear indication that the slab has been exposed to too much heat and, consequently, is failing. Consider this, a 24" diameter spall averaging 3/4" deep weighs about thirty pounds. Clearly, no firefighter wants thirty pounds dropped onto his or her head from 8 feet high when crawling through a smoke filled room! Spalls usually expose reinforcing.
 
Subsequent fires then work on the reinforcing which eventually loses tensile strength. A structural concrete slab relies on both the compressive strength of the concrete and the tensile strength of the reinforcing steel. Once either property is compromised, the structural integrity of the slab is compromised. In summary, concrete deterioration progresses as follows. As a building absorbs heat, the walls and slabs expand. Rarely is the building designed to compensate for this extreme movement. Frequently, expansion cracks develop in the slabs and walls. Those cracks often do not present structural concerns. In addition, however, the products within the concrete (sand, cement and gravel) are all expanding and contracting at slightly different ratios. Further, the extreme heat begins to affect the cement binder holding everything together.
 
Eventually, the binder softens and particles of sand gravel and cement separate. When this occurs, fine cracks develop in an irregular pattern called crazing. When a slab shows crazing, it is a sign that the concrete is suffering from the heat. However, a structural problem may still not exist. Eventually, water and steam penetrate the slab through these cracks and micro-cracks. This moisture finds its’ way to the reinforcing steel that is critical to the strength of the slab. The reinforcing begins to corrode, developing pressure from crystallization within the slab. After a period of time, the bond between the concrete and steel fails, resulting in an un-reinforced section of concrete that is now simply hanging onto the rest of the slab. This is called a delamination. More water builds up in the void between the concrete and steel. When that water turns to steam, it blows the loose un-reinforced concrete off (a spall).
 
Again, reinforced concrete slabs rely on the great compressive strength of concrete and the tensile strength of steel. These elements must be bonded together. When concrete and steel are no longer bonded, structural slabs are severely weakened. We have inspected slabs that have entirely delaminated horizontally into two un- reinforced slabs above and below a mat of reinforcing steel that now serves no purpose except, perhaps, to act as a cage to keep the top layer of concrete from collapsing to the floor.
 
Many of the same reactions to heat and steam are ongoing inside masonry walls that support many slabs and roofs in burn buildings. Masonry generally deteriorates slower than concrete. This can be attributed to the fact that some concrete masonry products contain pre-fired materials that have already reacted to a considerable level of heat associated with manufacturing. Also, concrete block walls are relatively porous allowing vapors to pass without immediate cracking or explosion. Nevertheless, many, if not most burn buildings will show cracking in masonry bearing walls. These cracks are commonly found near the corners of buildings and generally do not present structural stability problems, though they should be repaired to prevent further deterioration. In many cases, an appropriate recommendation for these cracks is to saw cut a straight joint in the wall along the line of the crack and to simply leave it. This will act as an expansion joint to minimize future cracking in that area. Consult with your structural engineer.
 
Finally, Architects have included lights, doors, windows, handrails, etc. inside burn buildings that have all quickly failed. Doors and windows are a particular maintenance headache and must be thoroughly considered during the design stage. It is rare to see a seasoned burn building with doors and windows still in operable condition.

We’ve decided we needed to offer a basic understanding of issues to address when considering repairs of an existing live fire training structure (burn buildings or burn rooms) or the construction of a new live fire training structure for industrial fire training. Over the years these structures have been built all over the world, frequently utilizing minimal resources. These buildings are simple concrete and masonry shells in which firefighters repetitively ignite and extinguish fires during training exercises. The simplicity of the typical structure often results in a casual approach to its’ design and construction. Indeed, many burn buildings are expected to have a relatively short life of only two to perhaps ten years.Many burn buildings have been constructed over the last three decades for a number of reasons. Live fire training has become more sophisticated as firefighting and fire science continues to develop. Industrial Firefighter training has become more than an objective - it is now a mandate.

In the past, abandoned buildings (acquired structures) were burned down by fire departments as a training exercise. However, the supply of such buildings has dwindled and environmental regulations are so stringent that many departments find obtaining approval to burn acquired structures to be too much trouble. Finally, the number of firefighters required to protect a community increases in direct proportion to the general population. In growing communities, departments must continuously train new recruits and career personnel. This growth fosters the demand for additional burn buildings.An increased demand for training requires a new approach to burn building construction.

Departments now realize that the casual approach results in buildings that prematurely fail and become too great a safety liability to be used for fire training. Facility Managers often consider the structure to be a costly liability and a nuisance as opposed to an asset. The very nature of the use of the building often leads to neglect of the structure. These buildings endure the most abusive environments. People expect the impossible from these buildings and they send their most valuable assets (personnel) into the structures every week.

Still, it is rare that appropriate maintenance funding is allocated to ensure the structure is safely maintained. Police stations, fire departments, schools, governmental centers and recreation centers are all meticulously maintained.Yet, where personal safety is placed in jeopardy on a daily basis, there is rarely funding available to ensure the maintenance of a safe training environment for the very individuals who protect the safety of the general public.

We at High Temperature Linings have concentrated on developing a responsible approach to burn building design and construction for over fifteen years. We have visited hundreds of burn buildings and burn rooms and have repaired and/or protected nearly 200 industrial fire training structures. We have documented successes and failures and have been exposed to a lot of great ideas.

Our designs for new live fire training structures incorporate those ideas, as well as our developments in protective lining technology.Again, we have provided documents on our site and on this blog to stimulate your interest in conducting further research into properly dealing with existing live fire training structures or those that are being considered for construction. Limited details are provided our site (Learning Center page) but we encourage you to contact us with specific issues, concerns or questions. We will attempt to lead you in the right direction and continue to post useful content for you to be educated on.

Dear Chief Training Officer:

 

Bill Glover, President of High Temperature Linings, has been sitting on the NFPA Technical Committee on Fire Training for nearly ten years.  In his work with the committee, and in his participation as a member of design / construction teams on over one hundred new live fire training structures (burn buildings and burn rooms), Bill recognized that many in the fire service were using NFPA 1403, Standard on Live Fire Training Evolutions, as a stand-alone Standard Operating Procedure. In fact, NFPA 1403 is a broad standard that addresses many types of training, and different types of fire training structures and/or fire training props.  It is imperative that Standard Operating Procedures be developed by each fire training center that applies NFPA 1403 to the particular structure, and to each burn room within the structure, that is being used by the fire department.

 

Further, it is apparent that most fire training academies are exercising too little control of fuel loads and number of evolutions conducted in permanent fire training towers, and that many in the fire service do not have an appreciation for the critical nature of the radiant energy that is developed as multiple successive fire evolutions are conducted.  Many in the fire service believe that the installation of a permanent temperature monitoring system in the burn building allows training officers complete control in maintaining safe training environments.  However, it is important to understand that a relative rise in temperature does not equate to the same relative increase in radiant energy produced.  In fact, as temperatures increase, and as successive fires are conducted, the amount of radiant energy increases exponentially.  To date, there is not an effective means of measuring the radiant energy produced in a live fire training structure.  Further, permanently installed temperature monitoring systems are only relatively accurate in reporting actual gas temperatures that exist in different parts of a burn room.

 

Consequentially, Bill has encouraged the NFPA Technical Committee on Fire Service Training to include language in the 2012 edition of NFPA 1403 that will help to address this issue.  The new standard will require that "burn sequence charts" be developed to define fuel loads and number of evolutions that can be safely conducted in each burn room of the live fire training structure.  The standard will include the following language:

 

7.3.1 The AHJ shall develop and utilize a safe live fire training action plan when multiple sequential burn evolutions are to be conducted per day in each burn room.

 

7.3.2 A burn sequence matrix chart shall be developed for the burn rooms in a live fire training structure.

 

7.3.2.1 The burn sequence matrix chart shall include the maximum fuel loading per evolution and maximim number of sequential live fire training evoltions that can be conducted per day in each burn room.

 

7.3.3* The burn sequence for each romm shall define the maximum fuel load that can be used for the first burn and each successive burn.

 

7.4.4* The burn sequence matrix for each room shall also specify the maximum number of evolutions that can be safely conducted during a given training period before the room is allowed to cool.

 

7.3.5 The fuel load per evolution and the maximum number of sequential evolutions in each burn room shall not be exceeded under any circumstances.

 

High Temperature Linings encourages our customers to immediately take a pro-active role by taking the following steps:

 

1. Understand the difference between temperature and radiant energy.

 

2. Understand that you can create environments in permanent live fire training structures that ARE a threat to your turn out gear and your safety. Remember, a permanent live fire training structure is designed to withstand thousands of live fire training evolutions without seriously affecting the integrity of the structure. Consequently, if you are not planning and controlling your evolutions, the environments created could be worse than those encountered in actual structure fires. Quite simply, many structures would collapse under the same conditions.

 

3. Develop Standard Operating Procedures that apply NFPA 1403 to the particular structure that you use for your fire training. We are attaching a sample of what that SOP might look like. Of course, you must develop SOPs that apply to your specific structure. The burn rooms attachement is intended to simply offer ideas. 

 

We hope this information is useful to you, and we strongly encourage you to contact us with comments and/or recommendations.

 

Thanks, and please be safe!