Various

In explosive manufacturing, use, or related processes, there exist a variety of failure and hazard scenarios dependent upon the specific application, circumstances, equipment and/or materials involved. The following tests are required in some regulatory applications and have wide application in many differing environments. They are usually identified as necessary to resolve issues discovered during the hazards analysis of existing or proposed facilities, process, or products.

Bonfire

One of the many applications for this type of test is the UN Stack Test: A stack of packages of an explosive product or a stack of non-packaged articles is placed on a non-combustible surface (steel grate) above a lattice of dried wood wetted with diesel fuel. Sufficient wood is used to provide a 30 minute fire. Three aluminum screens are placed 4 meters from the edge of the stack. The fire is ignited and the material is observed for a) Evidence of detonation, deflagration or explosion of the total contents; b) Potentially hazardous projections; and c) Thermal effects (i.e. size of the fireball, etc.).

The standard test for transportation classification is conducted on materials or articles as they are intended to be packaged for transport to determine the hazards caused by an external fire. For in-process classification purposes, the test is used to see how a pile of unpackaged articles or substances in containers used for staging, process and/or onsite storage will react in a fire scenario. A pile or stack of an explosive product is placed on a non-combustible surface (steel grate) above a lattice of dried wood wetted with kerosene. Sufficient wood is used to provide a 30-minute fire. Aluminum screens are placed 4 meters from the edge of the stack when potential projectiles are present. The fire is ignited and the material is observed for: a) Evidence of detonation, deflagration or explosion of the total contents; b) Potentially hazardous projections; and c) Thermal effects (i.e. size of the fireball, etc.).
Reference: Transport of Dangerous Goods – Tests and Criteria

Bullet Impact

This test is used to measure velocities that result in reaction. Various slug and powder loading may be used. This test is applicable to solid propellant, base grains, uncured propellants, and explosives.

The sample is placed in a pipe with a threaded cap at both ends. A 0.30 caliber bullet is fired from 30 yards. Explosives which burn are considered satisfactory. Those that don’t are more desirable.

This test is used to evaluate the response of an explosive to the kinetic energy transfer associated with the impact and penetration by a given energy source. The test sample is subjected to a three-round burst fired at 856 m/sec velocity and 600 rounds/min rate of fire. Typically the test is repeated in three different orientations. The striking point for the multiple impact is selected so that the impacting rounds penetrate the most sensitive material and location. A post-test inspection of the test film and hardware is performed to evaluate the reaction.

Closed Bomb

The result of this test is a pressure / time plot. The vessel is capable of withstanding gun pressures. SMS can provide closed bomb testing in several sizes and for varied applications. The bomb has firing electrodes to affect ignition, a gas relief valve, and a pressure transducer.

Critical Diameter-Standard

This test is used to establish an explosive’s minimum dimension for propagating explosive reactions. This test consist of a metal pipe (schedule 40, seamless, class B, black, type A-53) of various inside diameters and varying lengths. The length is three times the diameter. Comp C-4 is used as a booster. Normally, the test shall be completed after three to five failures are obtained 0.25 inches below a diameter that has been previously detonated or propagated. This dimension is referred to as the critical diameter. Velocity probes, witness plates or other witness systems are used for detection.

Critical Diameter-Wedge

This test is used to determine the critical diameter of cured explosive. Critical diameter is defined as the diameter below which the propellant will not sustain propagation of a detonation. The sample is a rectangle bar of explosive with the aft end perpendicular to the sides, the forward end cut to a 370 angle (see Figure). Comp C-4 with width and thickness identical to sample end view, length tree times the end dimension plus 0.5 inch, packed to a density of 1.5 grams/cc is placed on the sample. The Comp C-4 is fired, as the detonation progresses toward the opposite end, the sample dimension decreases until the size no longer is sufficient to support propagation of the detonation reaction. The point at which propagation discontinues is used to calculate critical geometry and thus critical diameter.

Critical Height

This test is used to determine the critical height at which a low rate reaction transits to a higher order explosive reaction. This test consists of an igniter (flame) to supply the initial reaction and a variety of lengths and diameters of iron pipe to contain the test material. Using the same diameter, the height of the test material is progressively changed until the reaction goes from burning to explosion or detonation. The diameter is then changed and the progressive height change testing repeated.

A critical height test determines the burning distance that a substance requires in order to have an explosion. The test pipe for a critical height test is a schedule 40, mild steel, seamless pipe with a mild steel threaded cap on one end . Critical heights can be determined for different diameter pipe. A 12 gram bag igniter is placed at the bottom of the test pipe (in threaded cap), with ignition wires running up the inner length of the pipe to the top of pipe (open end). The test pipe is filled to within an inch of the top with propellant powder. The results of the tests are determined by inspection of the pipe apparatus. The test is concluded by running a minimum of three succeeding trials which produced a “no-go” result at a certain height level below a level which produced a positive reaction (explosion). This level is referred to as the critical height.

Deflagration to Detonation

This test is used to determine the tendency of a substance to undergo transition from deflagration to detonation. In this test, the sample substance to be tested is contained in a carbon steel pipe, capped at one end with a “3000 pound” forged steel pipe cap, and at the other with a 13 cm square, 8 mm thick mild steel witness plate which is welded to the pipe. A 5.0 g black powder igniter, with a nickel-chromium resistance wire loop attatched, is placed at the center of the vessel with the resistance wire loop attached to two insulated copper lead wires. These lead wires are fed through small holes in the wall of the pipe and sealed with an epoxy resin. The tube is placed in a vertical position and the igniter is fired by a 15 amperes current from a 20-volt transformer. Three trials are performed unless a deflagration to detonation transition occurs earlier. The test result is considered positive if a hole is punched through the witness plate.
Reference: Transport of Dangerous Goods – Tests and Criteria

Detonation Velocity

The result of this test is a pressure / time plot. The vessel is capable of withstanding gun pressures. SMS can provide closed bomb testing in several sizes and for varied applications. The bomb has firing electrodes to affect ignition, a gas relief valve, and a pressure transducer.

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 they are most likely to function on impact. Three drops are made on the unit 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.
Reference: Transport of Dangerous Goods – Tests and Criteria

EIDS Gap

This test is used to measure the sensitivity of an EIDS candidate to a specified shock level, i.e. specified donor charge and gap. The test consists of an explosive charge (donor), a barrier (gap), a container holding the test charge (acceptor), and a steel witness plate (target). A clean hole punched trough the plate indicates that a detonation was initiated in the sample, and a substance which detonates in any trial is not an EIDS.

EPA Office of Solid Waste Test Method 1030

For the preliminary screening test, an unbroken strip or powder train about 250 mm long by 20 mm at the base and 10 mm high is placed on a low heat-conducting plate. A gas flame (burner torch) is used to ignite the powder train at one end (minimum temperature 1000°C). If the material does not ignite within two minutes or takes longer than two minutes to burn 200 mm of the powder train, it is not considered a flammable solid. If the material ignites and propagates by either flame or smoldering through a 200 mm length in less than two minutes, a full series of tests must then be conducted to determine the burn rate. If the burn rate is greater than 2.2 mm/sec then the material is considered to be a flammable solid.

Gel Permeation Chromatography (GPC)

Gel Permeation Chromatography (GPC) is used to determine the amount of a reference sample in a given material. The reference sample is extracted from the material using a solvent and separated from the insoluble material using a combination of techniques (centrifuging, filtering, etc.). The extracted solution is separated from lower molecular weight compounds by injecting the extracted solution onto separation columns packed with porous material. A steady flow of solvent on the column system moves the sample through the columns.

As the compounds in the sample pass through the packing, the smaller sized compounds are delayed in the pores of the packing while the larger sized compounds are excluded from the pores and travel faster. The result is a size (or molecular weight) separation where the larger sized compounds exit the column system first followed by the smaller compounds. A refractive index (RI) and/or UV-detector are used to detect compounds as they exit the column system. A reference-sample standard of known concentration is used to convert the detector response to concentration and quantify the amount present.

Koenen

The Koenen test is used to measure the sensitiveness of solid and liquid substances to intense heat with varied confinement. The sample is placed into a specified sample tube. Flame is applied to engulf the sample tube at a known heating rate. The tube is heated for 5 minutes or until an earlier event occurs. The sample tube is examined to determine whether an explosion occurred.

Varying the orifice plate over the top of the sample tube changes the degree of confinement of the sample. The orifice sizes are changed until an explosion effect occurs, or the substance passes the test with the smallest orifice. Three trials are conducted with the size of orifice plate one size larger than the level where any explosion occurred. This level is considered the limiting diameter. The substance is considered to have explosive properties if the limiting diameter is 1.0-mm or more.

CO2, CO, NOX Gas Detection

This is used to detect reactions of test samples. A LIRA, Model 300 is used to detect any gas with a wavelength of 4 to 5 microns (2000 to 2500 cm-1). The LIRA is connected to a test sample to allow any gases from the sample to be pumped into the LIRA. The evolution of gases from a reaction of the test sample are detected by the LIRA and displayed on a meter which indicates the concentration of evolved gases. Any gas collected from the test sample which did not evolve from a reaction with a wavelength of 4 to 5 microns will result in erroneous results.

Low Level Shock/Low Energy Mechanical Shock

This test is used to determine if an explosive liquid or uncured propellants reacts when a shock wave passes through it. This test evaluates the material response of liquid explosives and uncured propellants to various levels of shock stimuli below 20 Kilo-bar. The data from this test is useful to compare the relative reactivity of two different materials. The test consists of a 1.25 quart stainless steel Baine-Marie pot that holds the test sample. A circular disc of Detasheet is used as an explosive donor. The shock stimulus from the Detasheet is attenuated by various thicknesses of stainless steel sheets in multiples of four (e.g. 4, 8, 12 etc.). The shock enters the test sample through the bottom of the pot. The maximum shock level that does not cause the sample to react is determined. For responses of explosive liquids or uncured propellants to energy less than the low level shock test, a gas accumulator may be used to propel the metal plate.

Modified UN Screening Burn Rate Test

The standard UN test is used to determine if a material might be included as a flammable solid for transportation classification. In this test, it is being adapted to provide a lateral rate of burn. A “V” shaped mold similar to the one shown in the figure is filled with the test material. Four or five sensors are placed along the train of material, so as to indicate the arrival of the flame front. The sample is ignited using a hot wire or small torch, at one end. Timing is from the first sensor to the remaining sensors, to arrive at a lateral rate of burn.

NOL Card Gap

The card gap test is used to determine the sensitivity to shock pressure of individual explosive ingredients, ingredient mixtures, and cured material. The test consists of a booster charge and blasting cap to supply shock pressure, a variable gap to attenuate the shock, a test material, steel tube container, and a witness plate to verify detonation. The sensitivity is determined by increasing the gap until the test material fails to detonate. The criterion for detonation is a hole punched through a steel witness plate. The Bruceton “up and down” technique is used to determine the 50% probability sensitivity value which is half-way between the detonation and failure cards. The card gap test was developed by the Naval Ordnance Lab (NOL) and is required for explosive hazard classification in accordance with TB 700-2, dated 19 May 1967. A PROBIT or TIL test may be performed.

The card gap test measures the sensitivity of sample to shock. Booster and sample are separated by various numbers of 0.01 inch cellulose acetate cards. Results are reported as the number of cards necessary to prevent detonation. 70 cards represent the dividing line between a high explosive (1.1) and a low explosive (1.3). The larger the spacer gap which still allows detonation of the sample, the more shock sensitive the material.. Values depend on test size, geometry of apparatus and density, void fraction and preparation of sample. The test gives an indication of relative sensitivities. Several tests have been developed covering a wide range of sensitivity. (NSWC small-scale gap test, LANL small-scale gap test, LANL large-scale gap test, PX gap test, etc.)
Reference: Transport of Dangerous Goods – Tests and Criteria

Oxidizing Liquids Test

The test for oxidizing liquids measures the potential for a liquid substance to 1) increase the burning rate of a combustible substance when the two are thoroughly mixed or 2) to form a mixture which spontaneously ignites. The liquid is mixed with fibrous cellulose in a 1:1 ratio, by mass. The mixture is then heated in a pressure vessel and the rate of pressure rise is measured with a pressure transducer. The reaction rate is defined as the time taken for the pressure to rise from 100 to 300 psi. The mean reaction rate of five trials of the mixture is compared to the mean reaction rate of five trials of reference oxidizing liquids. Reference materials include a nitric acid (65% solution) mixture, a sodium chlorate (40% aqueous) mixture, and a perchloric acid (50% solution) mixture. The liquid is not considered an oxidizer if the rate of pressurization of the vessel is slower than the nitric acid (65% solution) mixture. A packing group for each material is assigned based on the reaction time of the mixture compared to the reference mixtures. If the sample material spontaneously ignites or exhibits a mean pressure rise time less than that of the perchloric acid mixture, the sample material is assigned to Packing Group I. If the sample material exhibits a mean pressure rise time less than or equal to that of the sodium chlorate mixture and does not fall under Packing Group I, the sample material is assigned to Packing Group II. If the sample material exhibits a mean pressure rise time less than or equal to that of the nitric acid mixture and does not fall under Packing Groups I or II, the sample material is assigned to Packing Group III.

N.1 Readily Combustible Solids

For the preliminary screening test, an unbroken strip or powder train about 250 mm long by 20 mm at the base and 10 mm high is placed on a low heat-conducting plate. A gas flame (burner torch) is used to ignite the powder train at one end (minimum temperature 1000°C). If the material does not ignite within two minutes or takes longer than two minutes to burn 200 mm of the powder train, it is not considered a flammable solid. If the material ignites and propagates by either flame or smoldering through a 200 mm length in less than two minutes, then the material is considered to be a flammable solid and a full series of tests must then be conducted to determine the severity of reaction for purposes of packing group assignment.

Self-Accelerating Decomposition Temperature (SADT)

The purpose of a SADT test is to determine the response of a material sample when subjected to heat for a 7-day period. The SADT is defined as the lowest temperature at which self-accelerating decomposition may occur with a substance in the packaging as used in transport. A material which rises 6 °C (10.8 °F) above the test temperature is considered self-accelerating at the test temperature. The results of the test are package dependent due to the effects of packaging size, heat transfer, decomposition characteristics, etc.

70 mm Gun, 25 mm Gun, Shotgun

These tests are used to determine the impingement properties of explosive. The propellant sample is fired form the gun and impinged against a steel plate. The sample is then collected and analyzed. Data usually includes: requirements for propellant breakup, velocity of initiation, reaction conditions, and energy partitions of interest.

Thin Layer Propagation

For the preliminary screening test, an unbroken strip or powder train about 250 mm long by 20 mm at the base and 10 mm high is placed on a low heat-conducting plate. A gas flame (burner torch) is used to ignite the powder train at one end (minimum temperature 1000°C). If the material does not ignite within two minutes or takes longer than two minutes to burn 200 mm of the powder train, it is not considered a flammable solid. If the material ignites and propagates by either flame or smoldering through a 200 mm length in less than two minutes, a full series of tests must then be conducted to determine the burn rate. If the burn rate is greater than 2.2 mm/sec then the material is considered to be a flammable solid.

Time/Pressure

The Time/Pressure test measures the rate of reaction of a substance under confinement, and whether that reaction might lead to a deflagration. The test apparatus consists of an instrumented pressure vessel with a rupture disk. An electric match is connected to the electrodes on the firing plug. Black powder (50 mg) is usually added to assure initiation of the substance under test. For samples easily initiated with an electric match, the black powder was omitted. A 5-gram test sample is then placed in the pressure vessel. The pressure vessel is secured and the match is initiated. The pressure is recorded during the reaction. A time/pressure profile is obtained. Numerous explosives show a pressure rise from 100 to 300 psi in less than 600 ms (milliseconds). A substance is definitely considered to be an explosive if the time interval for the pressure to rise from 100 to 300 psi is less than 30 ms in any one of three trials. The rupture disk provides relief to the pressure vessel above 300 psi.

Transparent Pipe

This test is used to determine susceptibility of solid, granulated, or shredded propellant or other explosive with a specific surface to volume ratio and packing density to transit from burning to explosion/detonation in a closed vessel. A sample is placed in transparent tubing (usually Lexan). The length of the tube, instrumentation requirements, surface/volume and theoretical maximum density are all determined and listed in the test plan for that particular sample. Camera, x-ray, pressure, photo diodes, strain instrumentation, etc. are used to take measurements. Data is used to predict detonation probabilities.

UN Gap

This test is used to measure the sensitivity of a substance, under confinment in a steel tube, to detonative shock. In this test, the sample is contained in a carbon steel tube with the bottom closed by two layers of polythene sheet pulled tightly. The booster charge consists of 160 g of RDX/wax (95/5) or PETN/TNT (50/50). The tube is placed in a vertical position and the PMMA spacer is placed in direct contact with the sheet to seal the bottom of the tube. After positioning the booster charge in contact with the PMMA spacer, the detonator is fixed in place against the bottom of the booster charge and initiated. Two tests are performed unless detonation of the substance is observed.
Reference: Transport of Dangerous Goods – Tests and Criteria

Safety Management Services
SAFETY MANAGEMENT SERVICES, INC.
1847 West 9000 South, Suite 205
West Jordan, Utah 84088
Phone: 801-567-0456

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DOT/DOD Resource

Troy Gardner
Troy Gardner, PE, CSP
Chemical Engineer
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.

Testing Experience

Safety Management Services, Inc. (SMS) has experience in testing a wide variety of explosives and other hazardous materials, such as:
  • Agent, blasting
  • Air bag inflators
  • Air bag inflators, compressed gas
  • Articles, explosive (fuzes, detonating and cartridges, power device)
  • Boosters, without detonators
  • Explosive, blasting, type A-E
  • Flammable Solids
  • Igniters
  • Powder, smokeless
  • Propellant, solid
  • Rocket Motors
  • Waste, Substances, explosive
In addition to material characterization, SMS also has experience in providing testing and recommendations for In-Process Classification and DOT Shipping Classification.
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