ASTM E144-94
Standard Practice for Safe Use of Oxygen Combustion Bombs.
Scope
This practice covers methods for judging the soundness of new and used oxygen combustion bombs, and describes the precautions to be observed in oxygen bomb combustion methods.
This practice is applicable to all procedures in which samples are completely oxidized by combustion in a metal bomb containing oxygen under pressure. Whether there is conflict with specific precautions in individual ASTM methods, the latter shall take precedence.
The values stated in inch-pound units are to be regarded as the standard. The metric equivalent of inch-pound units may be approximate.
Physical Requirements
Initial Test
The manufacturer of oxygen combustion bombs for use in ASTM test methods shall furnish a certificate with each new bomb showing that it has satisfactorily passed the hydrostatic and proof tests described in Sections 3 and 4. When requested, the manufacturers shall supply evidence that the bomb is designed and constructed in accordance with recognized practices for pressure vessel equipment.
Periodic Inspection
All seals and other parts that are recommended by the manufacturer shall be replaced or renewed after each 5000 firing or at more frequent intervals if the seals or other parts show evidence of deterioration. The hydrostatic and proof tests described in Sections 3 and 4 shall be repeated if any of the following have occurred:
- Five thousand firings
- Firing with excessive charge of either sample or oxygen
- Ignition of any internal part of the bomb, including fuel capsule.
- The evidence of corrosion or surface defects which exceed 80% of the manufacturer's stated corrosion allowance for the bomb.
- Any change in thread tolerances of bomb enclosures which exceed the manufacturer's specifications.
Hydrostatic Test
Fill the bomb with water at room temperature and connect to a suitable hydraulic pressure system. Be sure that all air has been displaced from the bomb and from the connecting gas passages. Support the bomb so that the diameter at the midsection of the cylinder can be measured with a micrometer caliper, and the deflection at the center point of the bottom can be measured with a micrometer dial indicator. Apply water pressure which is 1.5 times the manufacturer's recommended working pressure test pressure of the bomb and check the bomb and pressure connections for leaks.
With the hydraulic system at atmospheric pressure, measure the diameter at the midsection of the cylinder and obtain a zero reading from the dial indicator in contact with the center point of the bottom of the bomb. Raise the hydrostatic pressure to test pressure and repeat these measurements, then release the pressure and take a midsection of the cylinder or at the center point of the bottom of the bomb, or if any of the bomb parts do not resume their original dimensions when pressure is released, reject the bomb as unsafe.
Proof Test
Record the outside diameter at the midsection of the bomb cylinder as measured with a micrometer caliper, then assemble with bomb for firing with a tablet or pellet of compressed benzoic acid that gives an energy release that is 1.5 times the manufacturer's recommended energy release limit. Admit oxygen slowly to an initial pressure that represents the manufacturer's maximum charging pressure, then submerge the bomb in water and check for gas leaks. If none appear, arrange the bomb for firing in a water bath protected by a heavy barricade.
Note Caution - This is a proof test with a twice-normal charge, therefore the operator must be fully protected in case the bomb should rupture when fired.
Fire the bomb and allow it to stand for 10 min while cooling water is circulated through the bath. Remove the bomb, release the residual pressure, open and examine the parts, also measure the diameter at the midsection of the cylinder. If any of the bomb parts do not resume their original dimensions after the test, reject the bomb as unsafe.
Precautions in Use of Bombs
Observe the following precautions in all oxygen bomb combustion methods:
Sample Weight
The total weight of combustible material (sample plus gelatin, firing oil, or any other combustion aid) shall not exceed the maximum energy release recommended by the manufacturer. Initial tests with new materials that might be expected to burn rapidly, or to have explosive characteristics, shall be conducted with caution using only a fraction of the allowable maximum sample.
The oxygen filling system shall include a pressure regulator or other automatic device to prevent overcharging beyond the maximum allowable pressure specified in the appropriate ASTM test method. There must be no oil or other combustible materials in this system. Check the pressure gauge or gauges for accuracy at regular intervals, or whenever there is any reason to suspect they are inaccurate. The bomb must not be fired if any over-charge of oxygen should accidentally be admitted.
Ignition System
The bomb must be completely submerged in water during firing, and the charge must not be ignited if there is any evidence of gas leakage. Draw the ignition current from a step down transformer or from a suitable battery , using the lowest practicable voltage recommended by the manufacturer. Control the circuit by a double-pole push switch that can be closed only when the operator presses the ignition button.
Safety Barricade
Protect the operator by a barricade when firing the bomb and for 15 seconds thereafter. The barricade shall consist of 1/4-inch (6.35mm) steel plate or other equivalent protective material.
