September-October 2007
   


Forcible Entry Update

By John Mittendorf

While researching new developments in forcible entry operations, two considerations have changed dramatically, and with the potential to effect major changes on the fireground, both from a positive and negative viewpoint as follows:

ROTARY SAW

Every firefighter is familiar with the rotary saw, its advantages and disadvantages. Although a rotary saw is a great tool for cutting metal, it has two major drawbacks when evaluating its ability to cut metal and various other materials. One, a separate blade is required for metal, wood, concrete, and so on. Most fire companies carry their rotary saw with either a wood cutting blade or a metal cutting blade. If it is necessary to cut a material that is different than what the blade on the saw is designed for, it is necessary to change to the appropriate blade before cutting. Secondly, composite blades (i.e., aluminum oxide) will wear quite quickly during a cut, and depending on the thickness of the metal and duration of a cut, it is often necessary to change blades during the operation. Additionally, a 14-inch blade will only cut to a depth of about 5.5-inches, and that is when the blade is new. Obviously, when a cut is initiated, the 5.5-inch cut rapidly decreases.

Recently, a new blade for rotary saws has proven to mitigate the aforementioned concerns by using a steel blade that is fused with diamonds. This blade is known as a “multi-use cutoff blade fused with diamonds.” So, what are the advantages over the venerable composite blade? Everything, except the cost is higher. One blade will cut anything, and a 14-inch blade will cut 5.5-inches for its usable life. While we are considering usable life, I personally witnessed the same 14-inch blade last for over two years after being well used! One additional advantage of the multi-use blade is safety. Composite blades are prone to disintegrate, often with unpleasant results. A great article to review on this condition is “Minimizing Risk In Forcible Operations” by Captain Bill Gustin, Miami-Dade, Florida, Fire Engineering, April 2005. Steel multi-use blades are not prone to break! Therefore, I can no longer recommend the composite blade.

WINDOWS

Windows are windows and glass is glass, right? Wrong? Since the advent of terrorism, windows and glass (or glazing) have subtly changed to the point that it is becoming a noteworthy problem for the fire service. Let’s take a few minutes and briefly review the common types of glass and then look at several newcomers. Window glass can be found in various configurations as follows:

  • Plate (or annealed) glass is the least expensive type of glazing and is used where strength is not required, as in most standard residential windows. It forms sharp shards when broken.

  • Heat-strengthened glass is stronger than plate glass but not as strong as tempered glass and is used where greater strength is necessary. When broken, it breaks into smaller shards than plate or annealed glass.

  • Tempered glass is heat-treated to increase its strength — about five times over that of plate glass. It is commonly used in glass doors and some windows, and forms small chunks of crystallized glass when broken. Tempered glass can often be identified by the word tempered in one or both of the lower corners.

  • Laminated (or safety) glass normally consists of a layer of polyester film sandwiched between two layers of glass, adding strength to the glass. Common applications for it are auto windshields and some glass doors. When broken, the glass will adhere to the plastic, minimizing the hazard of numerous sharp, loose pieces.

  • Wired glass has a wire grid embedded in it, significantly increasing its strength for security and fire resistance purposes. When broken, the wire grid tends to hold the broken pieces together.

  • Thermoplastic compounds (Plexiglas, Lexan, etc.) can be significantly stronger than glass of the same thickness. Such compounds are often used to replace glass when security is a concern.

  • Glass coating films or polyester window films are commonly 4.0 mm glass-coating films that are applied to glass windows in new and old buildings before or after the glass has been installed. The film is used for energy conservation, noise reduction, and protection from falling glass in earthquakes. Window-coating films will hold glass intact when broken.

  • Hurricane resistant glass is a specific type of glass that has become increasingly popular on the U.S. Eastern Seaboard after hurricane Andrew. This type of glass is typically comprised of laminated glass and may have a thicker laminate than many air-blast resistant window systems! Hurricane resistant glass is resistant against a 9-foot long 2 X 4-inch piece of lumber traveling at 30 mph, and a small object traveling at 90 mph.

Now, let’s look at several newcomers:

  • Air-blast resistant windows are a retrofit by the General Services Administration (responsible for managing federal office buildings, courthouses, etc) and other governmental agencies and are designed to mitigate the effects of flying glass in the event of an explosive terrorist attack. There are different methods being used to accomplish this degree of protection, but the most popular is a mechanically attached security film to the interior of a building and next to exterior windows. Another method used is a blast curtain made of a mesh of high-strength synthetic fiber that deploys over a window before the glass is projected into a structure.

  • Ballistic-resistant (bullet-proof) glass is polycarbonate clad with glass and is designed to resist forced entry by firearms of varying degree.

Now, let’s look at how we break and/or force entry through these varying types of glass.

  • Plate or annealed glass will break in large, sharp shards with conventional tools.

  • Heat-strengthened glass will break in smaller shards than plate or annealed glass and with conventional tools.

  • Tempered glass will crystallize and the window will either collapse or may be gently pushed inward using the flat portion of the axe head, which will cause the window to collapse. This glass is best broken by striking the corner with the pick of an axe.

  • Laminated glass, glass with window film, and wired glass will break; however, the glass will adhere to the wire, plastic laminate, or film and remain in the sash. To remove the glass, cut or break it (with an axe or other similar tool) across the top first, and then down the sides. Remove the glass and wire, laminate, or film with the axe.

  • Polycarbonate (Lexan). Since polycarbonate is 250 times stronger than safety glass, it cannot be broken in a traditional manner. If entry is necessary, use a carbide-tipped wood blade on a rotary or chain saw. Make the horizontal cuts first and the vertical cuts second by moving the saw at a moderate speed. If the saw isn’t moved at a moderate pace, the blade may bind.

  • Hurricane-resistant glass cannot be broken with traditional methods but can be easily cut with a rotary or chain saw with carbide teeth. However, beware of small pieces of glass that will be forcibly ejected by the saws, and at the minimum, be sure to wear face and eye protection and minimize the presence of exposed skin.

Now we get to the new stuff.

  • Air-blast-resistant windows can be broken and/or breached with conventional forcible entry tools, although the process will take longer than conventional windows. Conventional forcible entry tools are defined as a pickhead axe, halligan, etc. Additionally, remember that once the glass has been broken in this type of window, the fabric covering the window will have to be removed before access and egress are possible (this will also take additional time).

  • Ballistic-resistant glass can be a very tough customer to break or remove depending on the specific type. Tests have indicated that carbide chain saws were slow and carbide rotary saws were somewhat better than the carbide chain saw. Conventional forcible entry tools were not effective. Tests have also indicated that emergency escape is not an option for occupants or firefighters. This type of glass is making its appearance in standard commercial structures and residential homes. This type of glass should immediately raise two noteworthy concerns:

  1. As this glass is a viable option for protection of occupants (commercial and high-end residential homes), one should consider what additional money would be spent to guarantee the same level of protection for exterior doors.

  2. If this type of protection is encountered at a structure fire, the incident commander should be made aware that the windows (and likely exterior doors) are not able to be opened in an acceptable period of time.

For additional information on these types of windows refer to the report Firefighter Ingress/Escape Procedures and Training for Security Window Systems located on the Internet at:  http://www.nfpa.org/assets/files/PDF/Member%20Sections/Final_Report_Package.pdf

Chief Mittendorf is the author of “Truck Company Operations” and “Facing the Promotional Interview”. To purchase, return to the Main page and scroll down to Fire Engineering Books.

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