There are many uses for knowing the sensitivity of a material to impact, friction or electrostatic discharge (ESD). These purposes include:

For the purposes listed above, it is most beneficial if the data obtained from sensitivity testing are in engineering units. Although it is important to know if a material is more or less sensitive than another, much more value is given to the test data if they can be compared quantitatively. If the sensitivity of a material has changed over time, it is important to know by how much. This is especially true if there are criteria of performance to be met. In addition, if the data obtained from these tests is in engineering units, they can be readily compared to the potential energy stimulus that can be applied to a hazardous material during normal or abnormal operations. For this reason, we recommend testing using the ABL ESD machine, the modified BOM impact machine and the ABL friction machine.

Both threshold initiation levels (TILs) and PROBIT analyses can be determined for materials using the recommended ESD, Impact and Friction Tests.

Threshold Initiation Level Determination

For the purposes listed above, it is most beneficial if the data obtained from sensitivity testing are in engineering units. Although it is important to know if a material is more or less sensitive than another, much more value is given to the test data if they can be compared quantitatively. If the sensitivity of a material has changed over time, it is important to know by how much. This is especially true if there are criteria of performance to be met. Also, if the data obtained from these tests is in engineering units, they can be readily compared to the potential energy stimulus that can be applied to a hazardous material during normal or abnormal operations. For this reason, we recommend testing using the ABL ESD machine, the modified BOM impact machine and the ABL friction machine.

Probit Analysis

Once the TIL for a substance has been determined, additional trials can be performed within the data range of the TIL, to provide sufficient data for a PROBIT analysis. At least 10 trials are performed at each of five different energy levels above the TIL. The data received from these trials are statistically analyzed. The resulting PROBIT curve is given as the probability of initiation versus the energy input. The results are used to calculate margins of safety and the probability of initiation of the material from the tested stimuli. The curve obtained from the PROBIT is a more accurate representation of the reactivity of the material than the TIL alone. The value of PROBIT data far exceeds the effort.

The PROBIT information is normally used in conjunction with an analysis of the In-Process Potential (IPP). The IPP is the potential stimulus that can be applied to a hazardous material during normal or abnormal process conditions. The calculated stimulus input and corresponding probability of initiation is located on the curve. This value is used directly in a hazards analysis.

ESD Test

ESD testing is used to determine the response of an explosive when subjected to various levels of electrostatic discharge energy. Electrostatic energy stored in a charged capacitor is discharged to the test sample. The sample to be tested is placed on a special holder that assures the electrostatic discharge will pass through the sample. A capacitor is charged with a known volt potential (usually 5000 volts). The discharge needle is lowered until a spark is drawn through the sample. The approaching needle method is most commonly used because it best models the safety issues involved with ESD sensitivity. An infrared analyzer is normally used to determine sample initiation.
Reference: Picatinny Arsenal. Navy-Indian Head MD, all propellant programs, Allegheny Ballistics Laboratory.

The ABL and BAM Friction Tests are the two primary tests of this kind. Both methods are UN listed, however, the ABL Friction Test has been calibrated into engineering units, which enables analytical comparison of results. The BAM test is good for relative comparisons of material reactivity only.

We are able to test solid or liquid explosives at various velocities and at various pressures. We are able to test materials for friction sensitivity at ambient, cold or heated conditions. We also can test for sensitivity to friction at different humidities.

Friction Test (ABL)

In the ABL Friction Test, the sample is placed on the anvil, and a known force is applied hydraulically through a stationary wheel. A pendulum or motor drive is used to propel the sliding anvil at any of several standard velocities perpendicular to the force vector. Sample initiation is detected by visual means (spark or flame).
Reference: The Transport of Dangerous Goods: Tests and Criteria, second edition, United Nations Test Method 3 (b) (iii) page 108.

Friction Test (BAM)

The sample is placed on a rough ceramic plate and a force is loaded on the sample through a stationary ceramic pin, in contact with the plate. The plate is motor driven through a complete cycle pass beneath the pin. The test sample is subjected to the friction created by the rubbing of the pin against the plate. This method allows for ambient temperature tests of powders and pastes.
Reference: The Transport of Dangerous Goods: Tests and Criteria, second edition, United Nations Test Method 3 (b) (I) page 101.

Impact tests are used to determine the response of an explosive when it is impacted by a moving mass. This test simulates impact conditions in processing operations, wherein an explosive is subjected to a collision between moving components of the processing equipment, by normal handling operations, or by the inadvertent dropping of tools or equipment.

Two different impact tests are routinely performed. The Modified Bureau of Mines Test is used to obtain data in engineering units. The Bureau of Explosives Test is performed in order determine a DOT classification for the material tested (See DOT Classification.) Large scale impact tests can also be conducted. SMS is able to test samples at various thicknesses (both solids and liquids) and at ambient, hot or cold temperatures or at specified humidities.

Impact Test (Modified Bureau of Mines)

The Modified Bureau of Mines Test uses a 2-kg drop weight. The sample is placed on a fixed anvil. A hammer of known contact area is positioned above the sample and the weight is raised to a predetermined height and dropped. Normally, sample initiation is detected by audible or visual means or by infrared analysis of selected decomposition products. This is the preferred test apparatus and method for impact testing because the results are obtainable in engineering units, which enable analytical comparison and easy ranking of materials for sensitivity.
Reference: Allegheny Ballistics Laboratory and the Bureau of Mines.