What Every Firefighter Should Know About Explosives - Part 2

Many bombing incidents involve improvised explosive devices (IEDs), or homemade bombs. Firefighters should know about the triggering mechanisms of such bombs, as well as about bomb threats and bomb searches. Triggering mechanisms of IEDs can be located inside or outside of small or large...


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Many bombing incidents involve improvised explosive devices (IEDs), or homemade bombs. Firefighters should know about the triggering mechanisms of such bombs, as well as about bomb threats and bomb searches.

Triggering mechanisms of IEDs can be located inside or outside of small or large bombs. Bombs can look like explosive devices or be disguised as such objects as books, briefcases, letters or packages.

There are a variety of triggering mechanisms. It is important to leave untouched any suspicious-looking object and to notify the appropriate bomb disposal authorities:

  • A tremor switch is a device that senses vibrations around bombs.

  • An anti-probe switch prevents any metallic object, like a knife, from cutting into a bomb. Surrounding the bomb are two conductive layers of aluminum foil, with a non-conductive layer of such material as paper in between. A metallic object that cuts through the two conductive layers completes the circuit, detonating the bomb.

  • A baro switch completes the circuit when a bomb is subject to a certain atmospheric pressure. The most common one is a balloon encased in a container. As the balloon expands, it pushes a conductive plate into two electrical leads and completes the circuit.

  • A thermo-static switch operates at a given temperature and can be as simple as a wall thermostat.

  • A collapsing circuit detonates a bomb if any wire in the circuit is cut.

  • A magnetic switch operates if any metallic item is passed over or near the bomb. A simple stud finder will work.

  • A photo-electric switch operates if a light is shone into a package or if a package is opened, exposing the inside to light. Photo-electric switches can be bought in almost any electronics store.

  • An anti-opening switch will detonate a bomb if the package is opened or if a drawer or door is pulled open. A simple method is to use a clothespin with two thumbtacks wired to its open jaw. The jaws are held open by a wooden peg. The peg is either glued to the top of a lid or tied by a string to a door or drawer. As the peg is pulled out, the two jaws snap together and the circuit is complete, detonating the bomb.

  • A timing switch can be nothing more than a clock which, at a set time, activates the rest of a circuit. This allows the bomber time to place the bomb without setting it off prematurely. Once the bomber has hidden the bomb, he sets the timer to allow him enough time to leave the area. When the timer runs down, the bomb is armed. A second timing switch is used to activate the bomb.

Booby Traps

Several other items have been used against police officers and firefighters.

A firefly, which is technically not an explosive, consists of a gelatin capsule filled with calcium carbide and sodium that is dropped into a gas tank of a police car or fire truck. When the water in the gas tank dissolves the capsule, the calcium carbide mixes with the water to form acetylene gas. The sodium reacts with the water to burst into flame and ignite the acetylene gas. The resulting explosion ruptures the gasoline tank.

A shotgun shell with a BB taped over its primer and a fin or streamer on the top is sometimes dropped from roof tops onto firefighters below.

Fire extinguishers can also become explosive devices. For example, during an arson fire in a San Antonio, TX, pizza parlor, the author discovered a fire extinguisher filled with gasoline. Fortunately, there was no pressure since the powder had been removed.

Bomb Threats & Searches

The increasing number of bombings involving IEDs requires the public to know more about bomb threats and bomb searches. Today, any individual or organization may be involved in a bomb threat or in a bomb search.

Those in authority must be especially prepared for bomb threats. They should understand the motives of bombers and the two ways bomb threats are communicated.

A bomber’s motive for his or her actions can be important for authorities to know if they can determine the nature of the motive. A bomber’s motive can provide clues as to his or her intended target, the type of bomb being used, and the location of the bomb.

Revenge is a common reason for bombings. Feelings of revenge can come from a fired or a disgruntled employee, as well as from a person involved in a domestic dispute. A bomb threat based on revenge is usually aimed at a specific person or object.

Politically motivated bombings are increasing worldwide. With all of the political unrest today, this situation may not improve. Some political groups use terrorist techniques to spread their political message. Although these groups claim to be the true representatives of the people, they often strike unarmed civilians and non-military targets.

Insurance was once a popular reason for bombing but it has since decreased in frequency. For a while, it was in vogue to insure a family member for a large amount of money and then to send the person somewhere by airplane with a bomb in his or her suitcase. However, the use of explosives to destroy persons or property in order to collect insurance is rare today.

Extortion, the act of gaining money or favors through the threat of harm, is the motivation of some bombers. They threaten to destroy a person or property but offer to reveal the location of the bomb if they receive money. Such bombers often tell bomb threat recipients the location of the bomb, whether or not they receive payment for the information, so that recipients take their threats seriously. Then the bombers often claim they have planted other bombs and demand more money for information about their location.

Coercion, or forcing others to act against their will, is another motive for bombings. For example, labor groups have sometimes threatened companies with bombings unless the companies hire their members. They have also threatened workers who cross picket lines at strike sites. In addition, criminals use bomb threats or bombings to force businesses to participate in protection rackets or to eliminate competition. However, these types of bombings are designed to scare others and usually do not cause death or damage. Those who make threats want to avoid destroying their source of income.

Psychopaths, those who suffer a character disorder distinguished by amorality or anti-social behavior, are also motivated to use bombs. The reasons they use them are varied and only trained professionals can explain their behavior. Sometimes their need for power is the reason. Seeing their actions reported on television and radio or in the newspaper can encourage psychopaths and others to commit more crimes. This is a reason to reduce media coverage of bomb threats or bombings. The public’s need to know must be weighed against law enforcement’s desire to prevent future bombings.

Firefighters and police officers are often depicted as rescuers. However, they are as vulnerable to bomb threats as those they protect. Because such personnel represent the government to bombers, they can also be targets. The author, with over 30 years in the fire service, has noticed a change in the public’s attitude toward firefighters. For example, the author has twice been physically attacked, once at a church fire and once on an EMS run.

Firefighters have reported receiving police intelligence information that indicates the initiation rites of some gangs include shooting a police officer, firefighter or paramedic. Firefighters and EMS personnel are especially vulnerable in bomb situations since they do not carry weapons.

Types Of Bomb Threats

Bomb threats are usually communicated by telephone or mail. Bombs are rarely delivered in person, although this does happen.

If a bomb threat is communicated by telephone, the recipient should try to keep the caller talking as long as possible. The recipient should ask the caller to repeat the message in order to obtain more time to regain his or her composure. Many times, the recipient of a bomb threat loses the wording of a caller’s initial message due to the shock of the call.

A recipient of a telephone threat should ask when the bomb is going to explode (time is critical) and where the bomb is located and what it looks like. A bomber is often proud of his or her work and may brag about the bomb. The recipient should also inquire about the reason for the bomb. This may help establish the bomber’s motive and target.

While on the telephone, a recipient should try to identify background noise. The sound of music, traffic, aircraft, voices or other noises may provide clues as to the location of the call. A recipient should also pay attention to the voice of a caller to determine his or her age and gender, and note if the caller’s voice sounds calm or excited or if the voice or any distinguishing speech characteristics is familiar.

The time a caller hangs up should also be recorded by the recipient. Then, a person receiving a bomb threat should report it to the police, providing his or her name, address and telephone number so authorities can later make contact, if necessary.

Bombs sent by letter or package in the mail may involve any of the previously mentioned motives. Mail bombs sometimes have no return addresses or they have false return addresses. Those who believe that any letter or package looks suspicious should avoid handling it. They should clear the area and phone police authorities.

Bomb Searches

Those in organizations should have a plan of action to search for bombs. Lines of authority must be established to determine who does what. With such a plan, confusion and panic can be prevented.

Panic is often caused when people do not know what to do and what is happening. Calm leadership is the best way to prevent panic.

Managers of organizations should first contact fire and police department personnel for help in developing bomb search plans. Such managers should determine who has a bomb disposal unit and whether or not those in their own organization will be involved in the search process. Many fire departments do not become involved in the process, and rightly so. They should stand by in case a bomb does go off so they can extinguish any resulting fires and provide rescue services.

If emergency crews are disabled in an initial bomb blast, they can be of little use. In addition, emergency crews are not familiar with the area so they do not know what belongs in the building. Only those who live or work in the involved area have this knowledge. For example, in the 1960s, when the author was a firefighter riding the tailboard of a fire truck, firefighters made bomb searches. None of the personnel, including the officer, knew exactly what they were trying to find.

Bomb search teams consisting of members of the company or residents of the area should be formed. Such teams should conduct searches of areas in buildings where explosives might be placed. A traditional fire escape plan is needed in case of evacuation. Once the plan is developed, it must have the approval and support of management, particularly when it comes to drills and training.

Search teams should be thoroughly trained and familiar with their search areas. Assignment to a search team should be voluntary. However, these activities involve the loss of work time and require the cost of equipping the search teams. In addition, managers should provide some compensation for such service, either in time off or extra pay.

Equipment For Searches

A minimum amount of equipment is necessary to search for bombs. The following list may be helpful.

A flashlight is a requirement because many of the areas to be searched will be in the dark. Extra batteries should be available since batteries in the flashlight may not work when needed. Batteries can also be left out of the flashlight until they are used, thus preserving them.

It is critical that the search teams have keys to every room and closet in their area of responsibility.

A fishhook tied to a fishing line can also be used to open doors and drawers. Several hooks can be soldered together to form a grappling hook. Picture-frame hooks or C hooks can be used with the fishing line to act as a fulcrum. Care must be used as the hooks may permanently damage the surface to which they are attached.

Tape may be used for several purposes. Searchers can tape an X over windows that cannot be opened. Windows near a suspected bomb should be opened or taped to prevent the glass from fragmenting from the blast. Tape can also be used to mark a room that has been searched.

A stethoscope can be used to listen to drawers for the ticking of the clockwork of a bomb before the drawer is opened or a door or a panel is removed. However, many bomb triggering mechanisms do not make any sounds.

Screwdrivers are needed to gain access to ventilation panels and other equipment.

Search Procedures

Search teams should work in pairs. They should be so familiar with their area to be searched that they can identify any object that does not belong there. They should divide the building to be searched into zones. The teams then should be assigned to certain zones. The outside of a building must also be searched. It should be designated a zone in itself.

A command post should be established in a secure area with telephones for communications. Two-way radio transmissions cannot be used since the electromagnetic radiation from them may detonate the bomb. Fire and EMS personnel should stand by at a safe distance to respond quickly in case of a bomb’s detonation.

Once a command post has been established and search teams have been given their assignments, the search should begin. Where to start is a matter of judgment. However, the evacuation path and the evacuation area should be searched first. This will provide a safe path from the building to the evacuation area.

In searching the outside of a building, a team should examine all drainage pipes, mailboxes, shrubs, trash cans and vehicles. Such utility connections as gas and electricity should also be searched. Electrical generators and transformers and boiler rooms are prime targets. Bombers think about hiding bombs in places that will do the most damage.

In searching vehicles, teams should look under fenders and under vehicles. Mirrors can assist them in looking for trip wires to hood, door or trunk areas. Latches on such car parts can be opened remotely by taping the latches of such parts in an opened position and using rope to pull them open. However, this can be extremely hazardous since any movement can set off a bomb. In addition, a bomb may be detonated remotely by a bomber who is watching from a distance.

Once teams have searched the outside of buildings and the evacuation area, they should search the command post area, along with the hallways, lobbies, restrooms and other places accessible to the public. (Searching restrooms is an unpleasant job but the bomber may place bombs in trash containers or used sanitary napkin containers, knowing the reluctance of the search team to check such areas. A broomstick can be used to search through the materials in such containers without using one’s hands. Gloves should also be used.)

Removable ceiling panels are ideal areas in which to place bombs. Searchers should look for ceiling tiles that are out of place, as well as for dust on the floor or furniture. Dust may have resulted from the bomber’s removing the ceiling tiles, planting a bomb and then replacing the tiles.

Search team members should also look for recently removed screws. If the screws are painted over, they have not been removed. If the paint on the heads of the screws appears to be scraped or broken, one can suspect a bomb inside the panel.

Conducting A Room Search

With two-person teams, each room can be divided into two zones. The bottom zone consists of everything from the floor level to eye level. Search team members should look under carpets, furniture and lamps and in trash containers.

The top zone starts at eye level and extends to the ceiling. Search team members should look behind curtains and at window ledges. They should inspect light globes and remove suspected ceiling tile to check the ceiling space. They should also inspect air vents for signs of tampering.

After teams have completed the search in their zone, they should change zones with their partners and repeat the process. After both zones have been searched by all members of the team, they should use tape or chalk to mark the room to indicate it has been searched.

If team members find suspicious-looking objects, they should avoid moving or touching such objects. Instead, they should notify the command post, either by telephone or a means other than two-way radio. They should provide the location and a description of the objects.

Then, search team members should open doors and windows around the object to dissipate the blast wave if a bomb does go off. If windows cannot be opened, they should place a large X of tape across the face of the window. This will help prevent the glass from fragmenting into tiny slivers. They should then evacuate the immediate area above, below and adjacent to the bomb site. The size of the suspected bomb, the construction of the room and other factors will determine the size of the danger zone.

Teams should continue to search even after a suspected bomb is found. There may be other bombs, or the object found may be a decoy. Only after all areas have been searched is the work of a search team completed.

Evacuating Buildings

The decision to evacuate is most difficult to make. Only the authority responsible for the people under its care should make this decision, not the emergency personnel. This will include such people as school principals and corporate managers.

One major problem occurs when a bomb threat involves an office building housing many different businesses. Establishing who is the authority in charge is sometimes difficult. In such a situation, public safety personnel may have to assume the responsibility for making the decision to evacuate.

Such a decision depends on many factors. Among the most important is the information from the bomber’s phone call and the authenticity of the call. If a suspected bomb is found, the size of the bomb becomes a factor. In addition, one must consider the type of building and the quality of its construction. In a well-constructed, fire-resistive building, it takes an enormous number of explosives to cause a structure to collapse. A large number of explosives would be difficult to hide and would be readily seen.

The decision to evacuate a building should be considered with care. The occupants of a well constructed building are often safer remaining in a room of the building than exiting hallways or standing around outside the building. A bomber may have planted a bomb in the hallway or at the evacuation site.

Pre-determined evacuation routes may have to be changed, depending on the location of the suspected bomb. The evacuation area should be safe and secure and out of the weather for the comfort of the people. Personnel should not be allowed back into the building until the permission has been given by the proper authorities.

The decision to turn off gas and electrical power during a search must be made with the requirements of the search teams in mind.


Mike Pickett is a San Antonio, TX-based fire and safety consultant. He also teaches part time in the Fire Science Program at San Antonio College, where he was an associate professor from 1970 to 1995. Since 1970, he has also worked with the San Antonio Fire Department. Part 1 of this report was published in the September 1995 issue.

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