At first glance, it may seem that venting or forcing entry in the front of a commercial occupancy consisting largely of glass doors and show windows doesn`t present much of a challenge–simply break the glass. After all, glass is one of the least expensive building materials and usually offers little resistance to breakage when proper techniques are employed. However, we should not always smash our way into a building, and when forcing entry does become necessary, it must be done safely and effectively–it is not always as easy as it may seem.

Breaking glass improperly or when it is not warranted can adversely affect fire behavior, personnel safety, and property conservation. For example, once a window or glass door is broken, we lose control of that opening and the flow of oxygen to the fire. Breaking storefront windows before effecting vertical ventilation can precipitate a backdraft and expose personnel operating directly in front of the fire building to flying glass and the force of the explosion. Broken glass leaves a building vulnerable to thieves and the elements.

At most fires, extensive glass breakage is seldom warranted. It can cost more to repair than the damage caused by the fire, prevent ventilation by positive pressure, and be perceived as unnecessary damage by the public. Breaking glass for ventilation or entry will be safer, more effective, and appropriate when it is preceded by a thorough size-up that takes into account the following factors: the type of emergency, fire conditions, and the type of glazing on the glass.


The type of emergency determines the urgency of the situation and, accordingly, the speed at which the building must be entered and the amount of damage that will be acceptable in gaining entry. Automatic fire alarms, water leaks, and a slight odor of gas or smoke are examples of calls at which it may be hard to justify breaking glass, especially in those instances when someone with a key to open the business can arrive in a reasonable period of time. Forcible entry in less-than-urgent situations is most appropriate when it is accomplished “through the lock,” which will be addressed later.


Make no mistake. Conditions that warrant extensive glass breakage must be immediately and accurately identified. Glass should not be spared when fire fills a structure with volumes of thick, billowing, pressurized smoke. These conditions require aggressive breakage to relieve a structure of toxic, flammable products of combustion; improve visibility; and provide an alternate means of escape.

Buildings have been destroyed because officers overly concerned with criticism over property damage left glass intact, impeding ventilation and allowing fire to takes possession of the structure.

How much glass to break is determined more by the pressure at which the smoke is escaping from a building than by the amount or color of the smoke. A small contents fire involving synthetic materials such as plastics, foam rubber, or vinyl upholstery can generate considerable dense, dark smoke, but the smoke will tend to drift gently out of openings because it is relatively cool. Often, the most effective and least damaging way to purge a building of this smoke is to leave the glass largely intact and ventilate with positive pressure. In contrast, smoke that pushes out of openings indicates a hot, intense fire and warrants extensive glass breakage in the attempt to save the building.


Glass must be broken in a controlled, systematic, and professional manner. Wind direction, timing with vertical ventilation, and the potential for backdrafts are critical considerations that will have an impact on how, when, and where to break storefront glass. Generally, firefighters are advised to position themselves upwind of the window and to break show windows across a storefront from the leeward to the windward side. An important exception to this general rule is when there is a potential for a backdraft. In this case, firefighters must avoid operating directly in front of the storefront show windows. Breaking glass under backdraft conditions should be done off to the sides of the storefront, out of the range of flying glass and heavy smoke, which can suddenly erupt into fire when it mixes with a fresh source of oxygen. Use a pike pole that is at least 10 feet long or the force of a powerful stream to break the glass from a position of relative safety.


Fire companies arriving at an early-morning fire in a closed commercial occupancy should expect a serious fire, due to a delay in discovery, and a fire that is likely to have progressed to the smoldering state because it has been deprived of an adequate supply of oxygen. Such conditions are favorable for a backdraft and may be identified by smoke puffing under pressure from around doors and other openings and glass that is stained black by soot and hot to the touch. Breaking glass when these conditions are present can precipitate a backdraft, or at least a rapid intensification of fire, once oxygen is allowed to flow into the building.

To relieve backdraft conditions, roof ventilation prior to opening the storefront is strongly advised but, unfortunately, it is not always possible to accomplish this with today`s construction and low fire company staffing levels. For example, a store exhibiting backdraft conditions may be located in a strip mall built in recent years with lightweight truss construction. As a practical matter, if a fire is severe enough to warrant roof ventilation, it is probably too dangerous to place firefighters on or under such a roof structure, which is prone to early collapse.

Then there is the issue of resources. Many fire departments outside of the big cities are neither staffed nor equipped to perform roof ventilation in a timely manner–that is, prior to or simultaneously with fire attack and before the fire has dangerously weakened the roof structure. Fire departments lacking the ability to fight fire in “textbook” fashion must realize their limitations and adapt strategies and tactics so that they can use their resources in the safest and most effective manner. Fire officers with limited resources must size up a fire, such as one burning for a prolonged time in a large, closed-up commercial structure, with realistic expectations of how the fire will behave and what they can and cannot accomplish. When you encounter hot, sooty glass, expect a backdraft and a fire that will rapidly intensify beyond the control of handlines. A first-due engine company arriving to find such conditions in a large commercial building must resist the inclination to rapidly enter the storefront with a handline. Rather, an extra alarm or mutual aid should be requested immediately, the apparatus should be positioned at a hydrant to secure an adequate water supply, and a heavy-stream device should be set up from a defensive position. No glass should be taken until additional companies arrive. The strategy here, from the onset, must be purely defensive to safely match firefighting resources to conditions.

Losing a building due to inadequate resources may be unavoidable and, therefore, excusable. There is no excuse, however, for losing the lives of firefighters by sending them inside a large, unoccupied, and inadequately ventilated commercial building under heavy fire conditions.


A window or glass door presents no reliable visual indication of the type of glass it contains. The type of glass is important, however, because different glazing materials require different breaking techniques and behave differently when they are broken.

Plate glass. The most common type of glazing used in storefront windows and doors, plate glass, breaks into very sharp jagged pieces. Improperly breaking large storefront windows can yield large falling shards that can severely cut a hoseline or a firefighter. Fragments of plate glass remaining at the top of a show window frame can fall unexpectedly and cause serious injury.

Due to the hazards of plate glass, most building codes now require storefront doors and adjoining windows to be glazed with a material that presents fewer hazards. Some new buildings, particularly in areas prone to windstorms, may not contain any plate glass. Unfortunately, firefighters have no reliable way of knowing if storefront windows are plate glass or not. Requirements for stronger, safer glazing materials apply only to new construction and replacement windows. But requirements themselves do not ensure compliance. For instance, in my jurisdiction, store owners have been known to “go cheap” by having an unscrupulous glass contractor replace broken windows and doors with plate glass, in violation of the building code.

It is therefore critical that firefighters who can`t be certain of the type of glass they will be breaking assume that the window or door is of plate glass and to use the following safe techniques:

–Use the reach of a long pike pole for safety. Stand to the side, upwind of the show window.

–Strike the glass at the top, and work down. This technique limits the size of glass fragments that will fall or possibly slide down the handle of the pike pole.

–Strike the glass lightly at first. Hot glass fails easily, and it can be difficult to stop the momentum of a long pike pole once it breaks through the glass. Measured impacts will reduce the chances of a firefighter`s losing his footing or control of the tool.

–Be sure to clear the frame of any remaining glass that can fall on firefighters or cut them when they pass over the windowsill.

Tempered glass. This type of glass undergoes a heat-treating process to increase its strength and reduce its hazard when broken. Tempered glass shatters into small, crystallized fragments, which are safer than broken plate glass. But breaking tempered glass is not without risk. The heat-treating process places the surface of tempered glass in tension and compression. When it is broken, tempered glass tends to “explode” as these forces are dissipated. Flying glass fragments can be propelled several feet, possibly finding their way into firefighters` eyes or open collars. Eye protection is imperative, and firefighters should always wear full protective clothing when breaking tempered glass or any glazing material.

Thick, heavy tempered glass show windows are incredibly strong. They can resist the strongest blows with a blunt object but can fail relatively easily when struck properly with a pointed instrument. Turn the hook of your pike pole away from the surface of the glass and strike the top of the window or door with the very tip of the point. The glass is most vulnerable when the smallest surface of the tool is used. Use a fast, sharp jab, not a full swing; this will impact the glass with the greatest velocity.

Protective films. Ordinary plate glass and tempered glass can be made more resistant to high winds and flying objects by applying a special film to its inside surface. Striking the glass will cause it to shatter, but the film will keep the glass largely intact. To remove the glass, use a short chopping or punching motion with the pike pole, beginning at the top and working down each side.

Laminated safety glass. Safety glass is becoming very popular for aluminum-glass storefront doors. Safety or “hurricane-resistant” glass is laminated, similar to vehicle windshields, and as such requires similar techniques for breaking and removal. Use short, chopping strokes with an ax, along the sides of the window or door. This technique, of course, is almost impossible to employ on large show windows; thus laminated glass poses an additional problem in ventilating buildings. (For additional information, see “Hurricane-Resistant Glass: Firefighter-Resistant?” by Mike Reimer, Fire Engineering, January 1996.)

If glass does not fail by any of the methods previously described, it probably isn`t glass.

Polycarbonate. Doors, windows, and skylights are commonly fitted with polycarbonate plastic in areas where burglaries and vandalism are problems. Polycarbonate is also known by the trade names LexanT or PlexiglassT. Polycarbonate may look like glass, particularly when it is new, but it is virtually impossible to break by striking with a tool. Striking the middle of a sheet of polycarbonate can cause a tool to bounce back with considerable force, possibly injuring firefighters working nearby. A rotary or chain saw equipped with a carbide tooth blade/chain can readily cut through polycarbonate. On aluminum-glass storefront doors, the impact of a maul directed in a bottom corner of the polycarbonate can drive the plastic out of its molding or the molding off the inside of the door.

A more meticulous technique, when time allows, involves prying the outside molding off the door with a screwdriver or the adz of a halligan. This permits the polycarbonate sheet to be removed and reinstalled to secure the building.


The aluminum-glass door is most commonly used for the fronts of mercantile occupancies. “Storefront” doors are usually secured with a pivoting deadbolt lock that is recessed or mortised into the aluminum frame or stile of the door. Pivoting deadbolts commonly project 112 to two inches into a receiver or strike in the doorjamb or adjoining double door. Although techniques for forcing storefront doors vary with fire conditions, security devices, and the tools available, one rule applies in all situations: Forget about prying aluminum-glass storefront doors! All you will manage to do is break the glass and unnecessarily damage the aluminum frame. A push bar across the inside of the door gives the door a lateral rigidity that almost guarantees that you will fail at your attempts to pry a long deadbolt out of its strike.

Given the strength of the lock and door assembly, the question naturally arises: Why don`t we just break the glass? Breaking the glass is an option, of course, and can be entirely appropriate when fire right inside the door requires an immediate application of water.

But breaking the glass out of a storefront door has drawbacks. First, it causes a big security headache for the businessman and fire and police officers prior to his arrival. Efforts to board up the opening take time, leaving the building unsecured. Second, breaking glass allows an uncontrolled flow of oxygen to the fire. Third, after the glass is broken, the opening will still be obstructed by a push bar that impedes quick egress because it catches on firefighters` SCBA tanks. Fourth, breaking glass may not get you in at all. In my response district, for example, aluminum-glass doors are commonly fitted with burglar bars or heavy steel mesh.

The preferred method of forcing storefront doors is definitely “through the lock”–that is, remove the lock cylinder and operate the pivoting deadbolt mechanism with a tool. Lock cylinders in storefront doors offer little resistance to removal because they are made of soft brass and screw into the lock with very fine threads. A small setscrew holds the cylinder in the proper position so that the rotating cam at the back of the lock cylinder will engage and operate the deadbolt mechanism.

The fire service has been using the “K” tool to pull lock cylinders for years. Other tools, such as the “A” tool lock puller and vise grips used to unscrew the lock cylinder, are also very effective. Some fire companies carry a variety of cylinder-pulling and lock-manipulation tools in a bag or tool roll known as their “forcible entry” or “through-the-lock” kit. This is a good idea because no tool or technique will work every time. For example, a doorjamb that projects beyond the surface of the door or a steel mesh can prevent a “K” tool from getting a “bite” on the lock cylinder. A tapered ring that fits behind and surrounds the lock cylinder prevents gripping the lock cylinder with vise grips and can make it difficult to drive a lock puller behind the lock cylinder.

Once the lock cylinder is removed, it is a fairly simple task to reach in with a screwdriver or special “key” tool, depress the spring that holds the deadbolt in the locked position and pivot lever arm from the 5-7 o`clock or 7-5 o`clock position, unlocking the door.

The through-the-lock method of forcible entry is usually fast and easy to perform on most storefront doors–perhaps it has been too easy. Burglars are well aware of the pivoting deadbolt`s vulnerability, and the lock industry has responded by offering several devices that fit over or around a lock cylinder and prevent it from being pulled or unscrewed. Cylinder guard devices are typically bolted to the door and, when the bolt heads are exposed, can be cut with a rotary saw equipped with an aluminum oxide blade. Attempts to chisel the bolt heads with an ax blade or adz of a halligan usually are not successful and frequently result in damaging the soft aluminum door frame and breaking the glass.

When a lock cylinder is recessed in a cylinder guard, trimming, or the edges of a security mesh, they can sometimes be removed by driving a screwdriver into the key plug and then twisting the screwdriver to unscrew the cylinder. The success of this technique depends on how tightly the setscrew holds the cylinder in the lock assembly. If the setscrew has a firm “bite” on the lock cylinder, the cylinder cannot be unscrewed with a screwdriver. But it`s worth a try; it only takes a few seconds to find out if it can be unscrewed.

Whenever a cylinder guard or any device prevents you from pulling a lock cylinder on a storefront door, an alternate method that always works is to saw through the pivoting deadbolt with a rotary saw. Cutting a deadbolt will be faster and easier and won`t damage the door or jamb if you enlarge the gap between the door and jamb by gently tapping in an ax blade just enough for the aluminum oxide blade to spin freely. Don`t be deterred by a cylinder guard that covers the gap between the door and jamb; simply saw through it.

Double aluminum-glass doors equipped with panic hardware can be easy to force without damage if they meet in the center without a center jamb or astragal. Insert a hook fashioned out of welding rod or other ridged wire between the doors, and then rotate the tool to exert a pull on the panic bar to open the door.

* * *

Storefront glass is relatively easy to break. But how we break glass, how much we break, and when we should break it can only be determined by conducting a thorough size-up that considers fire conditions, the nature of the emergency, and the type of glazing on the glass. Examine storefront glass carefully. It can tell you what conditions are like inside a building and sometimes how the fire will behave when the glass is broken.

Become familiar with the glazing materials and the door and lock assemblies in your response area. Finally, consult with locksmiths and glass contractors in your community. They can provide valuable information that can make venting and forcing entry in glass storefronts safer, easier, and more effective. n

Firefighters are breaking storefront glass to get ahead of a rapidly spreading fire. Wind direction, the type of glazing, timing with vertical ventilation, and the potential for a backdraft are critical considerations that influence how, when, and where storefront glass is broken. (Photo by Raul Torres.)

(Left) Firefighters beat a hasty retreat before the heavy smoke, mixing with a fresh supply of oxygen, erupts into flame. (Right) Abandoned handlines burn when the building lights up. Companies regrouped for a defensive attack. Examine storefront glass carefully as part of your size-up. It can tell what conditions are like inside a closed-up building and sometimes how a fire will behave after the glass is broken. Hot glass darkened by soot and dense smoke pushing under pressure indicate a hot, intense fire. (Photos by Raul Torres.)

(Top left) When you are not certain of the type of glass used in storefront show windows, use the techniques for breaking plate glass: Use the reach of a long pike pole, stand to the upwind side of the window, and strike the top of the glass. (Photo by George Izquierdo.) (Top right) Tempered glass can resist the strongest blows with a blunt object but fails relatively easily when struck with a pointed instrument. To break tempered glass, turn the hook of the pike pole away from the surface of the glass and strike the top with the very tip of the point. Use a fast jab to impact the glass with the greatest velocity. (Photo by Michael Heller.) (Middle left) Protective film applied to the inside of the glass keeps tempered glass largely intact. It can be removed by short punching or sawing motions. (Photo by George Izquierdo.) (Middle) A rotary saw equipped with an aluminum oxide blade readily cuts through the polycarbonate glazing in a storefront door. (Photo by George Izquierdo.) (Middle right) On aluminum storefront doors, the impact of a maul or eight-pound ax directed, first, in the bottom corner can drive polycarbonate plastic out of its molding or drive the molding off the inside of the door. (Photo by Michael Heller.) (Bottom) A more meticulous technique is to pry the outside molding holding the polycarbonate glazing off the door. The polycarbonate can then be removed and later reinstalled. (Photo by Michael Heller.)

(Top left) The “K” tool is an excellent tool for pulling lock cylinders. Here, it is being tapped into place over a pivoting deadbolt cylinder. (Top right) An “A” tool lock puller is effective when a doorjamb projects beyond the door`s surface or when burglar mesh (bottom) prevents a “K” tool from getting a “bite” on the lock cylinder. No tool or technique will work every time. (Photos by Michael Heller.)

(Top left) Vise grips can quickly and easily unscrew lock cylinders from most storefront doors. (Photo by Justin Wasil-kowski.) (Top right) A lock cylinder recessed in a cylinder guard can sometimes be unscrewed by driving a screwdriver into the key plug. (Photo by W. Stephens.) (Middle row) When a cylinder guard prevents you from pulling a lock cylinder, an alternate plan that always works is to saw through the pivoting deadbolt and the portion of the guard that covers the gap in the door. Cutting the dead bolt will be faster, will not damage the door and jamb, and will not bind the blade if you enlarge the space between the door and jamb with an ax blade just enough to allow the aluminum oxide blade to spin freely. (Photos by author.) (Bottom left, right) The lock cylinder on this storefront door is recessed between the projection of the doorjamb and the steel security mesh, preventing removal by a lock puller or vise grip. Sometimes, the lock cylinder can be removed by driving a screwdriver into the key plug and turning the screwdriver to unscrew the cylinder. (Photos by W. Latimore.)

(Left) The hook device slipped between the double doors locked with panic hardware is used to push the panic bar. (Right) Slipping the adz of the halligan between the doors facilitates insertion of the hook device. (Photos by George Izquierdo.)

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