Page 59 - JSOM Winter 2022

For this study, a breach is considered successful when no addi- behind the entire shape of the charge, with two 1000mL bags
tional tools, explosions, or work (e.g., kicking a partially de- per charge section, for a total of six charge sections, thus total-
stroyed door) were needed after detonation for the breaching ing 12L of tamping. Bags were laid parallel to the C-4 charge,
team to access the entry. Thus, we propose the following: forming a triangle over the charge block. To account for the
limited number of measured detonations (one per condition),
Hypothesis 1: water tamping will increase the breaching suc-
cess rate from blasts of the same construction on the same three rows of sensors were used to measure the blast. This
target type. portion of the course occurred in an open area environment
with no notable topography or man-made structures nearby
Hypothesis 2: water tamping will lower the observed over- to contain or reflect the blast aside from the structure being
pressure from blasts during breaching in locations where breached. Sensor stands were placed at the shielded and un-
breaching personnel are located. shielded minimum safe distance (MSD) for each individual
charge. At the unshielded MSD, two sensor stands were placed
at 45° off the wall at 40 ft from the charge on the left and
Methods and Data
right sides. At the shielded MSD, one sensor stand was placed
Ten blasts using water-tamped (n = 5) and -untamped (n = 5) directly in front of the charge 90° off the wall at 26 ft from the
breaches were evaluated across two different data collection charge. The breaching stacks were positioned at 40 ft from the
sites from 2017 to 2018. Eight additional charges from a third charge 45° off of the wall on the left and right sides. Sensors
site collected in 2016 were considered for comparing overpres- were positioned at the height of the center of the charge.
sure from tamped and untamped charges.
Data Collection 2:
During training, explosive charges of various shapes and sizes Spring 2018, Military/Law Enforcement Training Facility
were detonated repeatedly to measure overpressure. Generally, Similar to collection 1, charges evaluated were conducted as
explosives were a combination of pentaerythritol tetranitrate part of a larger course ( tamped = 4, untamped = 4). Charges
(PETN)-based 25-grain detonation cord (det cord; velocity of were placed on the hinge side of a door against the door and
detonation, 6,400 m/s), sometimes combined with either C1 or the frame using a 78-in × 2-in piece of 330B rubber. Two dif-
C2 detasheet (PETN-based flexible explosive; velocity of det- ferent weights of det cord were used: 25 grain and 50 grain.
onation, 7,100m/s). Regardless of the explosive construction When water was added as a tamp, a plastic sleeve containing
(det cord only or det cord + detasheet), explosives were deto- 3000mL of water was added to the back side of the linear
nated with M81-style Igniters and shock tubes in conjunction charge. The charges used in data collection 2 are considered
with J-1 or equivalent RDX (i.e., Research Department eXplo- light breaching charges. Three sensor stands were placed at
sive [cyclotrimethylenetrinitramine]) or PETN-based blasting 11 ft from the location of the charge for each door. Each stand
caps. When breaches were done with det cord only, strands was spaced 45° apart in a semicircle with the charge as the
varied in length but were generally 80-in long (i.e., door epicenter. Each stand had two sensors in incident orientation
length) and consisted of 1-strand (light breaching), 2-strand to the charge. The distances reported here, as was the case with
(moderate/solid core exterior door), or 3-strand (heavy exte- data collection 1, represent MSD for the construction of the
rior door) charges. Rubber sheeting was placed against the explosives used. The environment was open, with no reflective
door in all charges to function as a push, and when applied, surfaces to bounce pressure waves, and was fairly flat.
water tamps were same-length water bags made of flexible
plastic. Overpressure was measured using laboratory-standard Data Collection 3:
static and dynamic-pressure transducers (PCB Piezotronics) 2016, Law Enforcement Training Facility Site
and blast sensors (BlackBox Biometrics). Most importantly, Charges were three hockey puck–style (HP) charges composed
when charges were compared between tamped and untamped, of a 350-grain net explosive weight (NEW). The HP charge
the charge construction, weight, and position were identical was 7 ft of 50-grain det cord, spiraled up and placed on one
across conditions for that evaluation. B3 gauges are static cali- side of a 6-in × 6-in piece of 330B rubber. The rubber was then
brated at the factory across low, medium, and high ranges with placed against the target as a push. When water was added as
at least five data points and have been verified by the factory a tamp, 2 × 1000mL IV bags were placed on the back side of
to hold calibration over approximately 1 year or 1000 detona- the HP. Eight blasts (tamped = 4, untamped = 4) were evalu-
tions. The B3 also adapts to the environment by reading atmo- ated. Charges were placed on the lock side of the door against
spheric data as an additional calibration mechanism. Though a door frame in a semi-enclosed environment (i.e., three walls,
imperfect, it is notable that the B3 gauge has a transparent no ceiling), similar to an open-top shoot house/Hogan’s al-
self-calibration system. Measurement issues assessing pressure ley. Sensor stands were placed at 5 ft from the location of the
waves are a known difficulty, so having this documentation, charge because of environmental constraints. This distance
9
even if imperfect, provides increased transparency in science. was under MSD. All other aspects paralleled those of collec-
tions 1 and 2. Buildings were Conex shipping container style
Data Collection 1: Spring 2017, Military Facility (i.e., like freight cars) with doorways. Spacing was similar to
We evaluated a 21-day training course for military personnel that of US suburban environments, with reflective surfaces ap-
with a substantially heavy concrete wall- or fence-breaching proximately 22 ft opposite the charge.
component. The charges evaluated (tamped = 2, untamped
= 1) were conducted in a single afternoon but do not repre- Data Preparation
sent the entirety of charges detonated at the course. Charge Where possible, sensor readings are the reported average of
weights were 11-lb C-4/det cord combination charges; the C-4 multiple sensors with the same orientation and nearly identical
with det cord (totaling approximately 11 lb) was placed in a location in terms of distance. Data were reviewed for abnor-
roughly oval shape to provide an entry port through concrete. malities or sensor failures and compared with ancillary col-
When tamped with water, intravenous (IV) bags were placed lected data to ensure accuracy.

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