Explosive Building Demolition
Back to basic principles to solve a problem
by Capt Benjamin W. Klay
Marine combat engineers are capable of flattening any structure and of doing so with a level of collateral damage to surrounding structures that they can predict and scale according to the situation. Commanders with engineers attached must recognize this capability. Engineers must systematically train for it. The payoff is an extraordinary increase in the ability to shape the battlespace, clear fields of fire, destroy enemy fighting positions, and expand friendly positions.
During August and September 2006, 3d Platoon, Company A, 2d Combat Engineer Battalion (Combat Engineer Platoon, 3d Battalion, 8th Marines) developed and implemented building demolition techniques in Ar Ramadi, Iraq that enabled us to safely destroy 31/2 city blocks of abandoned buildings across the street from the Al Anbar Province Government Center. For years insurgents had used the buildings to stage complex, close-range attacks on the Government Center. Our operation, which was part of an engineer company operation, under Bravo Company, 16th Engineers, U.S. Army, that ultimately resulted in the demolition of eight city blocks of buildings, ended those attacks and removed from the city hazardous shattered buildings that someone would have eventually had to destroy anyway. The surrounding buildings—to include the Government Center—suffered broken windows, fallen ceiling panels, and other nonstructural damage but not to a level beyond the acceptable level anticipated.
Although our platoon had been extensively trained with explosives, we had not specifically trained to destroy whole buildings, and we didn’t have any publications specifically describing the principles behind expedient building demolition. We were able to accomplish our mission, though, by applying the basic principles of military demolitions described in Field Manual 5–250 (FM 5–250), Explosives and Demolitions; the basic principles of building construction; and the blast effects collateral damage estimates from the blast effects look-up tables. These can be found in the User’s Guide on Protection Against Terrorist Vehicle Bombs (Army National Guard, General Appendices, draft, November 1999, UG–2031–SHR) and the Joint Staff Integrated Vulnerability Assessment Security Engineering Toolbox (DTRA–01–03–D–0022, produced by ITT Industries, Advanced Engineering and Sciences Under the Defense Threat Reduction Information Analysis Center, December 2004).
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| Constant care must be taken in preparing charges during explosive ordnance disposal support operations. (Photo by SSgt Tracie G. Keesler.) |
As the platoon commander I initially had significant involvement in the planning. No established techniques existed for what we were doing, so the platoon’s leadership and I collaborated to help develop the techniques we would use. As the platoon got proficient, however, shot planning became an independent noncommissioned officer responsibility, with my involvement limited to giving orders, supervising, and inspecting while multiple squads reconnoitered and destroyed numerous buildings in a given night. What follows is a systematic list of steps for building demolition using our lessons learned.
First, conduct reconnaissance. Identify thickness, composition, location, and quantity or length of load-bearing members in the building to be destroyed. Identify the construction type for surrounding buildings that may be affected by the blast and determine their distance from the blast. Identify safe locations for friendly forces during the detonations. Identify civilian populations that may be affected by the blasts and the buildings or terrain that may buffer them.
The second step is to identify the maximum net explosive weight (NEW) per shot. This is accomplished by first determining an acceptable level of collateral damage to the surrounding structures, as defined in the blast effects look-up tables. The first blast effects look-up table (see Figure 1) offers qualitative descriptions of specified levels of collateral damage. The second blast effects look-up table (see Figure 2) converts each level of collateral damage into a scaled distance number for each type of building construction. Maximum NEW per shot can be determined by converting scaled distance to NEW using the following formula:
NEW = (Distance/Scaled Distance)3
NEW will be in pounds of explosives. Distance, in this formula, is defined as the distance, in feet, from the blast site to the building for which collateral damage is being determined. Thus, for example, an unreinforced concrete masonry building located 100 feet from a blast site can be expected to withstand minor damage from blasts consisting of NEWs ranging from 8.5 to 19.7 pounds. We derived these by first looking at Figure 2, according to which, minor damage to an unreinforced concrete masonry building can be expected for scaled distances ranging from 49 to 37 pounds. By inserting the distance, which we knew to be 100 feet, and the two scaled distances—49 and 37—into the formula, we were able to derive that our bracket for NEW would be (100/49)3 = 8.5 pounds to (100/37)3 = 19.7 pounds.
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Figure 1. |
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Figure 2. |
The third step—creating a shot plan—integrates the information from the reconnaissance and the NEW limits. In order to destroy a building using explosives, the explosives must directly target the building’s load-bearing members. Nonload-bearing members will be blown out by the blast overpressure, so they do not need to be targeted at all. The basic formulas from FM 5–250 are the basis for figuring out how to destroy a building’s load-bearing members. We only had to rely on two formulas, as the buildings the platoon destroyed were held up by reinforced concrete beams and/or load-bearing walls. Reinforced concrete beams can be taken out with counterforce charges according to the P = 1.5T formula, where P is for pounds of plastic explosive and T is for thickness of the concrete, rounded up to the nearest half of a foot. Load-bearing walls can be taken out using the P = R3KC formula, where P is for pounds of net explosive weight, R is the breaching radius in feet (this will be the thickness of the wall and will become one-half of the distance between which the charges are placed), K is a constant based on the material of which the wall is made, and C is a constant based on the means of tamping. Values for K and C can be found in charts in FM 5–250.
The platoon destroyed both single- and multistory buildings. In all but one of the multistory buildings, it sufficed for us to merely target the first floor. When the first floor collapsed, the higher floors flattened upon impact with the ground. There was, however, one two-story building for which, when the first floor collapsed, the second merely hit the ground intact, turning a two-story building into a one-story building that had to be destroyed using the same techniques. The determination of how many floors to target in a multistory building, then, should rely on an assessment of the sturdiness of the higher floors and the weight that will be coming down when the first floor destructs.
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| Blowing up insurgent arms, ordnance, and ammunition during Operation HEDGEHOG, January 2001. (Photo by Sgt Richard D. Stephens.) |
There are three major challenges to creating a shot plan. The first is to efficiently target the load-bearing members without either missing load-bearing members or wasting explosives on nonload-bearing members. Most of the buildings the platoon destroyed in Iraq were held up by skeletons of reinforced concrete beams that we could take down by applying counterforce charges to each of the beams. The buildings’ construction types were not obvious at first, but as the platoon became accustomed to working the area, we became highly skilled at figuring out what held a given building up. Through experience we gained general building analysis expertise and specific knowledge of the area’s construction techniques. In some cases, though, identifying a building’s load-bearing members was extremely difficult, especially in situations where nonload-bearing walls masked load-bearing columns or one wall among four was actually a load-bearing wall. In the worst cases a technique we used to help us identify a building’s load-bearing members was to put a small amount of explosives inside the building—anywhere from a single block of C4 (Composition 4) to a satchel—and detonate it. The overpressure would blow out nonload-bearing walls, often many rooms away from the blast and even to the exterior walls of the building, and leave intact the building’s load-bearing skeleton. This would make it extremely easy to identify what was holding the building up. It also had the added benefit of making the columns more accessible for the application of counterforce charges. The downside was that it could create a fire that would prevent us from working, create dangerous hazards to work around, or alert the enemy of our presence.
The second challenge was using the right amount of explosives on the building’s load-bearing members. Too much explosives is a waste that creates unnecessary collateral damage and expenditure of effort. Too little will leave a semicollapsed building behind. If there is great uncertainty as to whether a given amount of explosives will take down a column or wall, especially in the initial stages of a demolition project, it can be useful to test the P = 1.5T and P = R3KC formulas by targeting a small portion or single component of a building with some charges. It is much better for a single counterforce charge to fail to take down a column than to lace an entire building up with the wrong amount of explosives, only to leave it on fire and/or half collapsed. Because of these two uses of test charges—exposing the load-bearing members of a building and testing the demolition requirements generated by the P = 1.5T and P = R3KC formulas—it can be extremely useful to bring explosives on a reconnaissance mission.
Minimizing collateral damage is the third challenge during the creation of the shot plan. Shot plans must balance the values of tempo versus collateral damage. The perfect shot plan would require drilled holes and tamping for every charge, as well as a system of relays so the charges go off at different times, but this could take days, if not weeks or even months, to set up. At the opposite end of the spectrum is a shot plan in which massive amounts of explosives are strewn on every vertical surface of the building. This would almost guarantee that the building goes down and would require little planning, but it would generate massive collateral damage and would waste hundreds of pounds of demolitions.
The NEW limits determined in the collateral damage estimates will drive this aspect of the plan, as they will limit the size of any given shot so that only an acceptable predicted level of collateral damage will ensue. The platoon employed two techniques for destroying buildings, in one shot set, for which the required amount of explosives exceeded the acceptable NEW. The first was to set up two or more separate shots, each with its own initiating system. We would then detonate the two shots at virtually the same time. The split second differences in when the explosions would actually occur were enough to keep the collateral damage limited to that generated by the larger of the two shots. The second technique was to set up two separate shots and then connect them using an M15 delay blasting cap. (See FM 5–250 for more information on M15s.) The M15 consists of a length of shock tube with a low-density blasting cap located at one end and a high-density blasting cap at the other. The delay in initiation due to the low-density blasting cap is enough to create a split second difference in the initiation of the two shots that limits the collateral damage to that generated by the larger of the two shots.
Both of these techniques have the disadvantage of creating a substantially higher likelihood of misfire, due to the unreliability of the M15s and the possibility of the detonation cord getting cut by debris projected from the first of the two blasts. If a shot size mitigation technique involving split second differences in initiation times is employed, then the shots must be set up so as to prevent exposure to anything that could cause a misfire and so that the shot more likely to misfire is in a location more accessible for remediation procedures.
The completion of safety and evacuation plans is the final planning step. These should be guided by the planning factors described in FM 5–250. The blast effects look-up tables can also give additional insight into the hazards from shattering windows and debris.
These tools—knowledge of the basics of military demolitions, collateral damage, and building construction—are all that are necessary to flatten a building. Beyond that, the only limit to what a combat engineer platoon can destroy is the ingenuity of its Marines and their ability to instill trust in their commanders. No Marine should get hurt because an abandoned building creates cover, concealment, and obstacles for enemy employment. No one should get hurt because of the inability to predict collateral damage and take proper protective measures.
>Capt Klay has been in the Indivudual Ready Reserve since his separation from active duty in August 2007. He is now pursuing a master’s degree in public policy at Harvard University. He is a combat engineer officer and conducted two deployments to Iraq, first with 2d Marine Division G–3 (Operations) in 2005, then as the Combat Engineer Platoon Commander, 3d Battalion, 8th Marines in Ramadi in 2006.
