In-Process Tests

In-Process Test Series 1

The purpose of these tests is to determine the fundamental material characteristics in determining processing and handling hazards. These tests are conducted first since impact, friction, and ESD sensitivity data must be conducted on materials suspected of having explosive properties prior to handling them in the larger quantities required for the remaining test series. Impact, friction, and ESD sensitivity data, when compared to the in-process potential, can determine the margins of safety and therefore the level of risk achieved when manufacturing or using the material in processing.

Impact Test

Impact tests are used to determine the response of an explosive when a moving mass impacts it. 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.

The DOT and DoD use the Bureau of Explosives (BOE) impact machine to determine whether a material is too sensitive for transport by conducting a 10-trial screen test. This test is presented as a means used to obtain initial impact data for a manufacturing classification. However, a more thorough test using additional drop heights may be performed as needed in order to conduct a hazards analysis.

The UN prefers the BAM Fallhammer apparatus to determine the sensitivity of substances to impact. The material is forbidden for transport if the lowest impact energy at which at least one “explosion” occurs in six trials is 2 J or less. Using this or a similar impact apparatus, including various weights and heights; a more thorough understanding of the materials behavior to impact stimuli can be obtained as opposed to a screen test only conducted at one height using one weight.

Friction Tests

These tests simulate friction conditions that may occur in a process when an explosive is subjected to a frictional force between moving components or during material handling. The tests are used to produce friction profiles for the sample material. The two primary tests performed are the ABL and BAM friction tests.

In the ABL test the sample is placed on an anvil. Force is applied to the anvil through a hydraulic ram attached to a stationary wheel. A pendulum strikes the anvil and slides it under the wheel.

In the BAM friction machine, the force is applied to the sample by hanging weights on a lever arm attached to a pin. This pin is set on the plate containing the sample. An electric motor attached to the plate by a connecting rod slides the plate back and forth once under the pin (once forward and once backward).

Electrostatic Discharge Test

ESD testing is used to determine the response of an explosive when subjected to various levels of electrostatic discharge energy. The approaching needle method is most commonly used because it best models the common safety issues involved with ESD sensitivity. Electrostatic energy, stored in a charged capacitor, is discharged to the test sample by lowering the discharge needle until a spark is drawn through the sample. An infrared analyzer or sample consumption are means normally used to determine sample initiation.

In-Process Test Series 2

The purpose of these tests is to determine whether the material can propagate a detonation (zero-gap test) and if the test material will transition from a deflagration to an explosion under high confinement (internal ignition test). If the material has either of these explosive characteristics, it should be classified as an explosive in a manufacturing operation. If the material is shown not to have these explosive characteristics then the material may be classified as something other than an explosive, even though it may be sensitive to certain stimuli or still exhibit explosive reactions under extreme or rare circumstances. Substances, which are both explosive and easily initiated, should be considered a 1.1 for manufacturing applications.

Zero Gap Test

The test determines if a material will propagate a detonation when subjected to an adjacent detonation. The sample is loaded into a pipe facing a steel witness plate. A detonator is used to initiate a pentolite booster (50% PETN/50% TNT), which provides a known shock to the sample. The criteria for a “go” reaction are that the pipe is fragmented along its full length and/or a hole is punctured through the witness plate. The test is conducted two or three times unless detonation occurs. The UN gap test and the NOL card gap test can both be used for the same purpose when conducted at the zero-gap level.

Internal Ignition (20-Gram Bag)

The test determines if a material will explode or detonate when ignited under confinement. The sample is loaded into a pipe with 3000 pound pressure tested forged steel end caps. A 20-gram black powder bag igniter is inserted into the center of the pipe, the pipe is filled with test material and the ends capped. After the igniter is fired, if either the pipe or at least one of the end caps is fragmented into two or more distinct pieces then the test result is positive. The test is considered negative (the material passes) if the pipe is merely split open or the caps are sheared off in one piece. Three trials are performed unless a transition from deflagration to explosion occurs earlier.

In-Process Test Series 3

Test Series 3 is a compilation of tests to determine whether or not the material should be considered a high explosive (i.e. Division 1.1) or whether the material may be considered in a lower explosive category (e.g. Division 1.3). The test series contains four different tests: the thermal stability test, the small-scale burning test, the #8 cap test, and the card gap test.

Thermal Stability Test

This test is used to determine the reaction of samples when subjected to a mildly elevated temperature (75°C) for a specific period (48 hours). At the completion of the test, the sample is examined for discoloration, weight loss, and dimensional change as evidence of decomposition. Any evidence of explosion is also criteria for a positive result (i.e. fails the test).

Small-Scale Burning Test

This test is used to determine if unconfined samples, once ignited continue burning or transit to an explosion or detonation. A bed of sawdust, containing small samples of test material, is ignited and monitored. The test is a “go” (positive) if explosion or detonation occurs.

Explosive Cap Testing (No. 8 Cap)

The No. 8 cap test is used to determine susceptibility of explosives to detonation from the energy delivered by a standard detonator. Sample detonation is determined by examining the witness plate. The criterion for detonation (positive result) is that the witness plate is torn or penetrated.

NOL Card Gap Test

This test is similar to the UN gap test except that a shorter tube of material is used and a varied attenuator is placed between the test material and the pentolite booster. The attenuators provide a reduced shock source. The criterion for a “go” is that a clean hole is punctured through the witness plate. Typically, 12 trials are required to determine the 50% “go/ no-go” level. The test determines if a material will propagate an attenuated detonation.

In-Process Test Series 4

Test Series 4 is used to determine additional material characteristics which are used to define in-process parameters, in addition to those examined by the DOT and BATF. If the process is designed within these parameters, the maximum credible event from a Class 1.3 material or process is a mass fire hazard. The series also includes tests to determine venting parameters for confined operations. If, however, the process parameters exceed the critical height or critical diameter, then explosion of the material due to self confinement (from a flame initiation), or propagation of a detonation is possible.

Process Simulation

Where the process is known, appropriate process simulations may be used. However, a change in the process may necessitate re-testing of some or all of the explosive substances used in the process. Appropriate process simulations may consist of modifications to the standard tests below, to represent worst-case confinement, configuration, and/or loading in the process.

Critical Diameter Test

The critical diameter of an explosive is the largest diameter at which steady-state detonation cannot be maintained. The test uses varying diameter cylinders and a witness plate. A Comp C-4 or similar booster is used to initiate the sample. The test results are considered positive if the witness plate indicates detonation. Normally, the test shall be completed after three “no-go” reactions are obtained at a diameter one increment below a diameter that previously yielded a positive result.

Critical Height (Mass) Test

The critical height (mass) test is used to determine the critical height at which a flame initiation transits to an explosive reaction (explosion or detonation). In this test, a flame initiator (bag igniter) is placed at the bottom of a pipe assembly filled with the test material. Pipes of varying lengths and diameters are used to contain the test material. The test is performed by selecting a diameter, and progressively changing the height of the pipe until the material transitions from burning to explosion or detonation. The diameter is then changed and the progressive height variation testing is repeated. Normally, a curve can be fitted using the data, to predict the critical height for other diameters as well. A “go” reaction, for explosion, is one in which the pipe is damaged. The test is concluded at each diameter by running a minimum of three successive trials that produce a “no-go” result at a height below a level that produces a positive reaction (explosion). This level is referred to as the critical height at that diameter.

Internal Ignition (10-Gram Bag)

This test is similar to the internal ignition test described earlier except that a 10-gram bag igniter is used instead of the 20-gram bag. As stated previously, either the pipe or at least one of the end caps must be fragmented into at least two distinct pieces for a positive result. Three trials are performed unless a transition from deflagration to explosion occurs earlier. The test determines if a material will explode or detonate when ignited under confinement.

Koenen Test

Th Koenen test is used to determine the sensitiveness of a material to the effect of intense heat under vented confinement. In this test, the material is placed in a steel container with an orifice plate. The test apparatus is then placed in a protective steel box, and heated at a specified rate. A series of trials is conducted using different sizes of orifices. A “go” reaction is determined by examining the container. Conducting three successive “no-go” reactions with an orifice plate size above that which produced a positive result concludes the test. This orifice is called the limiting diameter. The limiting diameter may be used to evaluate the degree of venting required to avoid an explosion in the process.

In-Process Test Series 5

The DOT and DoD use the single package test, the stack test, and the external fire test to determine the hazards of a packaged finished article. These tests focus on the hazards of particular shipping and storage configurations. In order to assess unfinished articles in a processing operation or finished articles, which are not in their final shipping configuration yet, modified versions of these tests in addition to others should be conducted. The tests listed in this test series are required by the DOT and DoD to determine whether a packaged article is too sensitive for transport. For in-process classification, these tests are performed on the unpackaged, unfinished article

Thermal Stability Test

This test is used to determine the reaction of articles when subjected to a mildly elevated temperature (75°C) for a specific period (48 hours). At the completion of the test, the article is examined for evidence of reaction. Any evidence of explosion, fire, damaged outer casing, dangerous exudation of explosive visible outside the casing, or a temperature rise greater than 3°C above the oven temperature is criteria for a positive result (i.e. fails the test).

Drop Test

This test is used to determine if a finished or unfinished article can withstand a free-fall impact without producing any significant fire or explosion hazards. The test is not intended to evaluate whether the unit can withstand the actual impact. The article is dropped at an orientation in which it is most likely to function on impact. Three drops are made on identical units unless a decisive event (e.g. fire or explosion) occurs earlier. A test result is considered positive if evidence of initiation is identified. A rupture of the casing alone is not considered a positive result.

In-Process Test Series 6

Test Series 6 incorporates the single package and external fire tests used by the DOT and DoD to determine the hazards of a packaged finished article. For in-process classification purposes, suitable modifications are made recognizing this series is for unfinished articles. The in-process single package tests are termed worst-case propagation tests and several variations of the test are indicated. Usually at least three configurations are needed to effectively evaluate all the situations which can be encountered in the manufacturing process. The external fire test evaluates how the material reacts when initiated by an external fire.

Worst-Case Propagation Tests

This test is used to determine whether a reaction from an unfinished article, which was accidentally fired or initiated, would propagate to other articles or parts of the process. This test is conducted by placing articles in a worst-case configuration (e.g. side-by-side, end-to-end, and/or in a pile). This test is similar to the stack test except that the articles are tested without packaging, as they are or may be found in the process, including during process upset. The unfinished or finished articles are placed on top of a steel witness plate. Sand filled inert containers or sandbags may be positioned on the sides and top of the test articles for added confinement. Wire or clamps may be used to hold the articles in place. An article near the center of the unpackaged articles is caused to function (donor). Evidence of propagation or any other observable reaction is recorded. Normally at least two trials are conducted.

External Fire Test

A stack of unfinished or finished articles as they appear in the manufacturing line is placed on a non-combustible surface (steel grate) above a lattice of dried wood soaked with diesel fuel or equivalent source. A wire basket or clamps may be used to hold the articles in place. Sufficient fuel is used to provide a 30-minute fire. The fire is ignited and the material is observed for: a) Evidence of detonation, deflagration or explosion of the total contents; b) Potentially hazardous fragmentation; and c) Thermal effects (i.e. size of the fireball, etc.).

Protective-Enclosure Testing

The use of technology to mitigate hazards is supported in civilian and military practice. Devices can be designed to fully contain or safely direct the deflagration and/or detonation effects of limited quantities of explosive material. Quantities of explosive may thereby be afforded the same level of isolation and safety as provided by the traditional quantity-distance (Q-D) separations.

A blast chimney is an example of these technologies. A blast chimney or other technology must be made to withstand the maximum possible event plus a 25 percent overcharge from the type and configuration of explosive contained within, if used in lieu of Q-D separations.

Shielding devices are evaluated for the following (MIL-STD-398):

  • Blast Attenuation – 1) to provide protection from accidental detonation, shall be designed to prevent exposure of operating personnel to peak positive incident pressures above 2.3 psi (16 kN/m2) or peak positive normal reflected pressure above 5.0 psi (34 kN/m2), and 2) to provide protection from intentional detonation of ammunition, shall be designed to prevent exposure of operating personnel to impulse noise levels exceeding 140 decibles.
  • Fragmentation Confinement – 1) to contain all fragmentation or direct fragmentation away from area requiring protection, 2) to prevent generation of secondary fragmentation within areas requiring protection, and 3) to prevent movement, overturning, or structural deflections that could result in personnel injury.
  • Thermal Effects Attenuation – 1) to limit exposure of personnel to a critical heat flux value based on the total time of exposure (designated by the equation µ [cal/(cm2)sec] = 0.62t^(-0.7423), where t is time in seconds that a person is exposed to the radiant heat), 2) all operating personnel shall be located at a distance from the shield that assures their exposure is less than the heat flux determined from specified equations, and 3) the upper torso of an operator’s body shall not be subjected to any visible fire or flame; flame impingement upon the lower portion of the body may be permitted provided that the heat flux specified above is not exceeded.

Any overpressure discharged must be done so in a manner that safely directs or dissipates the effects thereof. A blast chimney or other technology must be made to withstand the maximum credible event from the type and configuration of explosive contained within, if used as workstation protection in lieu of separated or unattended operations.

Safety Management Services
1847 West 9000 South, Suite 205
West Jordan, Utah 84088
Phone: 801-567-0456

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Testing Resource

Kirt Sasser
Kirt Sasser, PE
Director of Engineering and Testing
SMS is one of five laboratories authorized by the DOT to witness classification tests for explosives (Class I). We also frequently run in-process tests. Testing is performed at our test site facility at the Tooele Army Depot where we have a thermal lab, sensitivity test lab, and large scale test area. Please contact us for further information at 801-567-0456 or by sending a request.

In-process Classification Guide

To download and view the full in-process classification guide in PDF format (169 KB), click below: "In-Process Hazard Classification of Explosives," K.N. Sasser, T.C. Speed, September 2005. In addition to in-process classification, SMS also has experience in providing testing and recommendations for DOT Shipping Classification and Material Characterization.
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