Page:30 CFR 1993.pdf/36

Mine Safety and Health Admin., Labor (h) Maximum temperature. In the normal operation of the blasting unit, the maximum temperature of any electric component shall not exceed 302 °F (150 °C).

(i) Capacitor discharge. The blasting unit shall include an automatic means to dissipate any electric charge remaining in any capacitor after the blasting unit is deenergized and not in use.

(j) Construction. Blasting units shall meet the acceptable performance criteria of the construction test of § 7.67.

(k) Locking device. The blasting unit shall be equipped with a locking device to prevent unauthorized use.

(l) Enclosure. The blasting unit enclosure shall be protected against tampering by―

(1) Sealing the enclosure, except the battery compartment, using continuous welding, brazing, soldering, or equivalent methods; or

(2) Sealing the electric components, other than batteries, in a solidified insulating material and assembling the enclosure with tamper-resistant hardware.

(m) Battery charging. Blasting units that contain rechargeable batteries shall have the following:

(1) A blocking diode, or equivalent device, in series with the battery to prevent electric energy in the battery from being available at the charging connector.

(2) The charging connector recessed into the enclosure.

§ 7.65 Critical characteristics.
The following critical characteristics shall be inspected or tested on each blasting unit to which an approval marking is affixed:

(a) The output current.

(b) The voltage cut-off time.

(c) The components that control voltage and current through each making and breaking electric contact.

(d) Operation of the visual indicator and the firing switch.

§ 7.66 Output energy test.
(a) Test procedures. The blasting unit shall be tested by firing into each of the following resistive loads, within a tolerance of +1%:

(1) The maximum blasting circuit resistance.

(2) Any resistive load between 3 ohms and the maximum blasting circuit resistance.

(3) One ohm.

(b) Acceptable performance. (1) The voltage shall be zero at the firing line terminals 10 milliseconds after operation of the firing switch.

(2) The electric current from the blasting unit shall be:

(i) Less than 50 milliamperes except during firing of the blasting unit.

(ii) Available only through the firing line terminals.

(iii) At least an average of 2 amperes during the first 5 milliseconds following operation of the firing switch.

(iv) Not exceed an average of 100 amperes during the first 10 milliseconds following operation of the firing switch.

§ 7.67 Construction test.
The construction test is to be per- formed on the blasting unit subsequent to the output energy test of § 7.86.

(a) Test procedures. (1) The blasting unit shall be dropped 20 times from a height of 3 feet onto a horizontal concrete floor. When dropped, the orientation of the blasting unit shall be varied each time in an attempt to have a different surface, corner, or edge strike the floor first for each drop.

(2) After the blasting unit has been drop tested in accordance with paragraph (a)(1) above, if shall be submerged in 1 foot of water for 1 hour in each of 3 tests. The water temperature shall be maintained within ± 5 °F (±2.8 °C) of 40 °F (4.4 °C), 70 °F (21.1 °C) and 100 °F (37.8 °C) during the tests.

(3) Immediately after removing the blasting unit from the water at each temperature, the unit shall be operated first with the firing line terminals open circuited, then operated again with the firing line terminals short circuited, and last, the output energy tested in accordance with the output energy test of § 7.66.

(b) Acceptable performance. (1) The blasting unit shall meet the acceptable performance criteria of the output

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