Disarming the Bomb, Part 12
Route Tampa and Al Nasiriya
BOOOOMMMMM!!!!!
The shot went off perfectly. It was just over 500 pounds of explosives and a lot of fragmentation. T-Bone and I went back to the shot hole to verify that all the items were consumed. There was nothing left. Not even the AK-47s. I was very surprised because obviously there aren’t any explosives in the AK-47s. Putting them on the bottom ensures that they get completely consumed by the intense pressure and heat from the detonation.
There’s one thing I need to explain before we move on with this journey. EOD is a highly technical job. In part 11, I talked about how important stacking ordnance items is. Everything needs to be tight!
There is more to tight stacking while doing these demolition shots. All demolition shots that EOD do are very calculated. Each ordnance item has a specific amount of explosives in weight. By knowing the amount of explosives in weight you can calculate safe blast and fragmentation distances. This is known as Net Explosive Weight, or NEW, and Quantity Distance Range, or QDR. NEW is needed to calculate QDR. I want to explain this to you because EOD isn’t just “go out there and blow stuff up.” We are professionals as it relates to preserving life and critical infrastructure. I’ll try to simplify the process so that it’s easy to understand.
Follow along, class is in session!
Every explosion is measured off of the power and detonation velocity of TNT. TNT stands for Trinitrotoluene. Every different type of explosive has different detonation velocities. The higher the detonation velocity, the more brisance or power the explosive has. Brisance is the shattering effect of a high explosive. In order to calculate blast and fragmentation effects, we utilize a measurement known as TNT Equivalency.
TNT equivalent is a convention for expressing energy, typically used to describe the energy released in an explosion. The tonne (metric ton) of TNT is a unit of energy defined by that convention to be 4.184 gigajoules,[1] which is the approximate energy released in the detonation of a metric ton (1,000 kilograms) of TNT. In other words, for each gram of TNT exploded, 4.184 kilojoules (or 4184 joules) of energy is released. (Wikipedia)
Next, we use a process known as Relative Effectiveness Factor, or RE Factor. The RE Factor relates an explosive's demolition power to that of TNT. The RE Factor enables engineers to properly calculate explosive weights needed to clear obstacles that impede military movements. For EOD, we use the RE Factor to calculate safe distances. Remember, all explosions are calculated using the power of TNT.
The next thing to understand is what we refer to as K-Factor. A K–Factor is a conversion factor calculated for various pressures expressed in pounds per square inch (PSI). The K–Factor is used to calculate the distance from the point of detonation to a given PSI value for an explosive weight. Aside from ordnance fragmentation, blast over-pressure can also kill.
K-Factor allows EOD to determine an exact distance where the blast over-pressure will not harm people or structures. Or it will inform us where damage will be done to structures within the blast radius. There are different K-Factors to consider:
K-18 is used to calculate safe distances for explosive breaching during tactical operations. K-18 equates to 4 PSI at a specific distance.
K-24 is used for EOD response operations. K-24 is used when you have one EOD technician that has to work downrange on an IED or UXO. You want to keep an eye on the EOD technician that’s working. It is the K-Factor used so another EOD technician always has eyes on the main EOD technician working. K-24 equates to 2.3 PSI at a specific distance.
K-50 is used to determine if a building or structure needs to be evacuated. If a building or structure is outside the K-50 distance, then there is no need to evacuate. K-50 equates to .95 PSI at a specific distance.
K-300 is used to determine the safe distance where fire and medical personnel should be staged. K-300 equates to .07 PSI at a specific distance. And lastly…
K-500 is used for fragmentation distance. It is the point where all non-essential personnel are evacuated. Blast effects from this distance will not be felt.
The last thing to consider when calculating explosive safe distances is that all explosive calculations use the cube root as a multiplier. The basic principle of cube root scaling is that the energy released from a point explosion will propagate with an expanding sphere of the shock wave. This is why a cube root is applied to explosive effects calculations.
Let’s review.
TNT equivalency is a measurement of explosive energy. RE Factor is the process of relating other explosives to TNT. K-Factor is a measurement of PSI at a specific distance. And cube root is applied to explosions due to spherical propagation created when detonation occurs.
Now then, let’s take, for example, one of the 155mm projectiles that I had in the shot that T-Bone and I initiated. To simplify the calculation for you, I’m only going to use one projectile. The M107 155mm projectile contains either TNT or Composition B. The explosive weight is 15.1 pounds. The particular projectiles in the shot we did contained Composition B.
The RE Factor for Composition B is 1.72.
15.1 times 1.72 is 25.97 pounds.
25.97 is the actual explosive weight or NEW in pounds.
Now, we get the cube root of 25.97, which is 2.96. T-Bone and I used the K-Factor of K-50.
2.96 times 50 is 148. So the safe blast distance or QDR for one M107 155mm projectile is 148 feet. At this distance, frontal and overhead protection is required. This distance is to determine the safe distance for blast over-pressure. But 148 feet was not a safe distance for fragmentation. That’s why T-Bone and I took cover behind the overpass; the 148 feet distance protected us from the blast, but hiding behind the overpass protected us from the fragmentation.
Easy days right?? So every time I mention any demolition shots, just know that this process is always applied.
Back to the story…
As T-Bone and I supported the supply convoy to Al Nasiriya we cleared 37 vehicles and eight weapons caches along Main Supply Route Tampa. Once the supply convoy made it to Al Nasiriya, T-Bone and I were tasked to support Mortuary Affairs, who were responding to an incident that occurred in an area known as “Ambush Alley.” This was the first time that we were operating in an urban environment. Up until this point, T-Bone and I were mostly responding to open desert areas.
Ambush Alley
The bloodiest day of the operations for the Marines was 23 March, when 18 men of Charlie Company, 1st Battalion, 2nd Marines, were killed and eight Amphibious Assault Vehicles were disabled in heavy fighting with Iraqi forces around the Saddam Canal.[10] The Marines were engaged by RPGs, mortar, and artillery fire, as well as four Iraqi tanks hidden behind a building.[11][12]
A friendly-fire incident occurred when two A-10s from the Pennsylvania Air National Guard strafed the amphibious assault vehicles of Charlie Company by mistake, killing at least one Marine, and possibly as many as 17 Marines, over the course of multiple passes.[13][14][15][16]
The A-10 strike was cleared by the battalion's forward air controller, who was with Bravo Company, bogged down on the eastern outskirts of the city. He did not have contact with Charlie Company and was unaware that Marines were so far north.[3][17] An investigation into the friendly-fire episode confirmed that friendly-fire was to blame, but "like most friendly-fire investigations, it was done... with no enthusiasm for determining what really happened, or who should be held accountable."[18] Videotapes from the A-10 planes went missing.[19] Despite the clear findings, the U.S. Central Command issued a press release which both minimized certainty and the role of friendly-fire.[20]
By 27 March, most Iraqi resistance in the city had been subdued and the focus of the battle shifted from full combat to cordon-and-search operations. Small groups of Fedayeen Saddam militia were hiding throughout the city and launched sporadic attacks on Marine patrols with small arms and RPGs. These attacks were uncoordinated and the resulting firefights were lop-sided, with large numbers of militiamen killed.[25] (Wikipedia)
It was the friendly fire incident from the A-10 that T-Bone and I were responding to. Our mission was to clear any UXO that was kicked out from the incident. I was extremely impressed with the Mortuary Affairs unit. When you think of the phrase, “leave no man behind,” the U.S Marines live up to that statement. Mortuary Affairs was going through the rubble and ashes to find anything that resembled human remains. They wanted to find any part of any Marine that died in that incident and bring them home. It was humbling to see them work. They looked like archeologists sifting through the surrounding area. They would not leave until every square inch was searched.
As the Mortuary Affairs personnel worked, T-Bone and I searched the immediate and surrounding areas for any UXO. The amphibious assault vehicle had an MK 19 grenade launcher. These launchers fired 40mm high velocity rifle grenades. These grenades are known as golden goose eggs in the EOD community. These are nasty pieces of ordnance to respond to. If you find one that has been fired, you cannot pick it up. They have a fuze that is referred to as “All the way acting” fuzes.
These fuzes are armed by setback and rotational forces. Once fired, they arm after 10 meters. They also self-destruct after 15 to 19 seconds. The self-destruct feature is what makes these very dangerous.
The Iraqi civilians in this area started to become curious. Crowds started gathering around the immediate area where we were working. We were trying to keep things calm and not anger the civilians. We didn’t know who was good, or who was bad. The 40mm grenades were everywhere. We had to determine if the grenades were fired or not. We did this by looking at the primers at the base of the grenade. If the primer didn’t have an indent, we knew it wasn’t fired. We couldn’t just blow them all in place like we wanted to. We had to gather as many as we could and blow them together with one shot.
“Hey brother, the crowd is getting pretty bad,” I said to T-Bone.
“Yeah, we gotta hurry this shit up,” he responded.
We started to try and keep the locals back. We would signal with our hands that there were explosive hazards by waving our hands frantically; they would just wave back at us.
“Fuck, man, this isn’t good, bro, we have to try something to get these people back,” I said to T-Bone.
T-Bone and I grabbed some charm candies. Our hope was that we would give the kids candy and hopefully they would back off. That didn’t happen. In fact, it made it worse. More kids gathered; the crowds got closer and closer. We definitely were outnumbered.
Suddenly out of the corner of my eye I saw these kids throwing something. They were playing catch.
“What the fuck!! T-Bone look!!!! They are playing catch with the 40 mike-mikes!!” I yelled.
“Oh shit!!”
We both ran towards them and chased them off.
“Did he drop it?” I asked T-Bone.
“Fuck man, I don’t know,” he said.
“Dammit man, we gotta do something!” I said.
I looked over at Betsy and there were a couple of Iraqis looking inside. I ran over to see what they were doing. T-Bone and I had a Sports Illustrated swimsuit issue on the dashboard of Betsy. These guys were very interested in the magazine. I shooed them back.
Finally we saw what appeared to be the village elder. The locals seemed to listen to this guy.
“Hey T-Bone, you see that guy?” I asked.
“Yeah, he seems like the head honcho,” T-Bone responded.
“I have an idea,” I said.
I called the guy that we thought was the village leader over to Betsy. As he approached I asked, “English? English?” The guy shook his head no.
Dammit, I thought.
I pulled out the magazine and showed it to the guy. His eyes got as big as eggs. He reached out for it.
“You get them back, I’ll give this to you,” I said to him.
“Okay,” he said.
“Wait, I thought you didn’t speak English,” I said to him.
He didn’t respond. But he grabbed a stick, went around, and got all the kids back. Cleared us a decent cordon.
“That worked awesome!” T-Bone said.
“Hell yeah!” I laughed.
The guy came back to Betsy.
“You give me, you give me,” he said.
“After, after,” I responded. He turned around and continued to keep people back.
“Let’s get this shit done!” T-Bone said.
We gathered up all the 40mm grenades that we found. We had a total of forty-three grenades. T-Bone and I picked the most remote area that we could find to set up our shot. The sun was starting to go down and we had to work fast. We dug out a hole to pack the grenades tightly. We set up our explosives and got our non-electric firing system ready and primed in. I pulled smoke, and shouted, “FIRE IN THE HOLE!!!!!!”
To be continued….