Explosivity Testing

Explosivity testing includes screening evaluations & differential scanning calorimetry.

Screening Evaluation
The screening evaluation consists of analysis of the chemical structure of a suspected explosive material and development of its oxygen balance. For this purpose, Chilworth typically employs a computer model known as CHETAH developed under the aegis of the American Society for Testing and Materials (ASTM). The model classifies materials as low, moderate, or high risk decomposers based on the enthalpy of decomposition, the heat of combustion, the oxygen balance, and other thermodynamic criteria.

Differential Scanning Calorimetry
Chilworth uses differential scanning calorimetry (DSC) or Accelerating Rate Calorimetry (ARC®) to determine the quantity of heat evolved during a thermally-initiated decomposition. This method classifies materials as self-heating, explosive, or detonable based on decomposition energy.

Impact Sensitivity Test – BAM Fall Hammer Test
Chilworth performs impact sensitivity testing using the BAM Fall Hammer apparatus developed by the German Federal Institute for Testing Materials (BAM). Impact energy is imparted to a 40mm3 sample by means of a falling weight. The limiting impact energy is determined as the lowest energy at which a flash, flame, or explosion is observed. The test is used to assess the sensitivity of the test material to drop-weight impact. The BAM Fallhammer test is a part of UN Test Series 3 which is used to assess the ignition sensitivity of suspected explosive materials. As many as 54 trials may be performed and therefore approximately 3 cubic centimeters (cc) of sample may be required.

Friction Sensitivity Test – BAM Friction Test
Chilworth performs friction sensitivity testing using the BAM Friction apparatus developed by the German Federal Institute for Testing and Materials (BAM). The test is used to measure the sensitivity of test materials to frictional stimuli. The test is a part of UN Test Series 3 which is sued to assess the ignition sensitivity of suspected explosive materials. A 10mm3 sample is spread on a porcelain plate and the plate is then dragged under a weighted porcelain peg. The force on the peg is varied and the limiting friction load is determined as the lowest force for which a flash, flame, or explosion is observed. As many as 60 trials may be performed, and therefore approximately 1 cubic centimeter (cc) of sample may be required.

Isothermal Storage Test
Chilworth uses isothermal storage testing to assess the thermal stability of a suspected explosive material. The sample material and an inert reference material are loaded into separate glass vessels and then placed in an oven at 75 degrees Centigrade (°C). Once both materials reach oven temperature, their temperatures are measured for up to 24 hours. The sample is deemed thermally unstable if the sample temperature exceeds the temperature of the reference material by 3 °C at any point during the test. Only one trial involving a 100 gram sample is performed, however additional screening tests may be undertaken to explore the behavior of the sample prior to the primary test. Therefore, as much as 500 grams of sample may be required. The isothermal test is a part of UN Test Series 3 which is used to assess the ignition sensitivity of suspected explosive materials.

Detonative Shock Test – BAM 50/60 Test
Detonative shock testing is used to assess the detonability of a material. Chilworth performs detonative shock testing using the BAM 50/60 apparatus developed by the German Federal Institute for Testing Materials (BAM). The sample material is loosely filled into a 0.5 meter (m) long steel tube having a 50 millimeter (mm) internal diameter (ID) and a 60 mm outside diameter (OD). The tube is then subjected to a detonative shock from a high explosive donor charge. The detonability of the sample is determined based on the damage to the steel tube and — if necessary — by measurement of the rate of propagation. Approximately one (1) liter of material is required for each trial.

Confined Heating Test – Koenen Tube Apparatus
Chilworth performs Confined Heating Testing using the Koenen Tube Apparatus. The test is used to assess the sensitivity of the test material to the effect of intense heat under confinement. The test is a part of UN Test Series 1 & 2 which are used to assess the explosiveness of suspected explosive materials. The sample material is packed into a 75 mm long steel tube having a 25 mm ID to a level 15 mm from the top. This sample amount is used in three equal amounts of approximately 9 cubic centimeters (cc) each. The tube is capped with an orifice plate and heated along its entire length by four (4) burners positioned around the tube. The orifice diameter is decreased from 20 mm until the increased confinement causes the reaction to burst the tube. The critical diameter is determined as the largest diameter for which an explosion is observed and is used as the criterion for classifying a material as “thermally sensitive.” The test is used to assess the sensitivity of the test material to the effect of intense heat under confinement.

Small Scale Burning Test
The small-scale burning test is used to determine the response of a substance to fire. Small samples of the test material are placed into a small plastic cup which is placed on a pile of kerosene-soaked sawdust. The sawdust is ignited and the behavior of the test material is observed. As many as four (4) trials may be performed — two (2) trials for a 10 gram sample size and two (2) trials for a 100 gram sample size. Thus, a minimum of 220 grams of sample is required. The small scale burning test is a part of UN Test Series 3 which is used to assess the ignition sensitivity of suspected explosive materials.

Time/Pressure Test
The Time/Pressure Test is one of three tests that comprise Test Series 1 and 2 of the United Nations (UN) protocol for the classification of explosive articles and materials for transport. The test is used to assess the effects of igniting a substance under confinement in order to determine if ignition leads to a deflagration with explosive violence at pressures that can be attained with substances in normal commercial packages. The test is performed using a specially-designed cylindrical steel pressure vessel (89 mm L x 60 mm OD). One end of the cylinder is fitted with a bursting disk and plug which are removed to introduce the sample, then replaced and secured. The other end of the cylinder is fitted with the firing assembly. The firing assembly is comprised principally of an electric fusehead and primed cambric. A pressure transducer is fitted to the cylindrical pressure vessel at the midway point between the top and bottom. The pressure signal during each trial is recorded using a microcomputer. A positive (+) result is indicated by a pressure rise from 690 kilopascals (kPa) to 2070 kPa in less than 30 milliseconds (ms). Three (3) trials are performed. Approximately 1 liter of sample is required to complete this testing.

UN Gap Test
The UN Gap Test is one of three tests that comprise Test Series 1 and 2 of the United Nations (UN) protocol for the classification of explosive articles and materials for transport. The test is used to assess the sensitivity of a substance under confinement in a steel tube to detonative shock. The test involves filling a cold-drawn, seamless steel tube (400 mm L x 48 mm OD x 4 mm t) with the test sample. The top of the vertical tube is covered with a mild steel witness plate. The bottom of the tube is fitted to a booster charge and detonator. A positive (+) result is indicated by complete fragmentation of the tube and/or holing of the witness plate. If a negative (-) result is obtained during the first trial, a second trial is performed. Approximately 1.5 liters of sample are required to complete this testing.