Electrical ignition tests

A 4.9 g sample of the liquid siloxane in a glass dish was put into a bomb calorimeter (on an open bench) containing 5 ml of sodium hydroxide solution to absorb combustion gases. The electric igniter system consisted of a metal wire in contact with a cotton-wool wick which dipped into the siloxane sample. The bomb was sealed, pressured up to 39-44 bar with oxygen, and the igniter was fired. A violent explosion blew the lid off the bomb (rated at 190 bar working, 250 bar test), and examination of the deformed bomb indicated that a maximum detonation pressure of around 900 bar had been attained. 

Given the unreliability of the stab-initiated tests, a second round of testing was performed using a hot nichrome wire to initiate the detonators in place of the NOL-130 stab mix and firing pin. This test was successful and all nine detonators functioned, showing that DBX-1 is more susceptible to this method of initiation. Figure 8 shows the electrical ignition setup. 

The former consists of an electrically heated vertical cylindrical tube (furnace), the top of which is connected to a small brass chamber containing the dust sample to be tested. A pneumatic system is used for blowing the dust downward thru the heated tube. In the usual ignition test, the lowest tube temp at which a flame appears at the lower mouth of the tube is taken as the ignition temp of the dust cloud. In the relative inflammability test the temp of the furnace is held constant at 700°C (1292°F) and only the amounts of Fuller s earth is decreased until no ignitions are observed... 

A large number of flammability tests have been developed to evaluate the ignition propensity of a wide range of materials exposed, usually for a short duration, to a small heat source. For example, the most recent compilation of ASTM lire standards includes 30 small heat source ignition tests.21 When adding methods that use an electric arc, hot wire, hot surface, etc., instead of a flame and those developed by other standard organizations (NFPA, UL, ISO, IEC, etc.), the total number of tests is in the hundreds. 

Igniter Tests. Assembled electric igniters intended for military use are usually subjected to the following tests, after selecting 10 samples for each test ... 

The sample of the propellant (or pyrotechnic mixture) is of the form of a long, thin strand, which is inhibited laterally in order to bum like a cigarette. The strand diameter is usually from 3 to 10 mm. During the test, the strand is attached to the holder, which is fixed to the locking cap. After the desired pressure inside the combustion chamber and the desired temperature of the chamber are achieved, the sample is electrically ignited. 

International fire and flammability test standards are developed by the International Organization for Standardization (ISO) and the International Electrotechnical Committee (lEC). The latter is concerned with electrical products only. Technical committees TC 92 and TC 89 are the primary committees that develop and maintain fire and flammability test standards in ISO and lEC respectively. As in ASTM, there are a number of product- or industiy-specific committees in ISO that also develop fire and flammahihty test standards. For example, SCI on Test Methods of ISO TC 136 on Furniture has puhhshed two ignition tests for upholstered seating. An important difference between ISO and lEC vs ASTM and NFPA is that the international committees establish consensus on a geographical basis. Each coimtiy that actively participates in the work can be a voting member on an ISO or lEC committee. Committees are composed in a similar manner in CEN and CENELEC, which are the European coimterparts of ISO and lEC respectively. However, member coimtries can have multiple votes in CEN and CENELEC committees. The munber of votes is a function of the population of the coimtiy. 

In comparative tests the CWS and NDRC models showed approximately the same range, sixty yards with thickened fuel and one-third of this with ordinary fuel. The former model was slightly heavier and held less fuel than the latter. The Army preferred the rugged CWS model with pyrotechnic ignition to the light NDRC model with electrical ignition, and adopted it as the standard model, M2-2 in March 1944. ... 

When using a gas test flame, light the pilot flame and the test flame and adjust the test flame to 4 mm (Vn in.) in diameter. If the instrument is equipped with an electrical ignition device, adjust according to the manufacturer s instructions. 

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