Digital ohmmeter for testing blasting circuits

September 17, 1990

MEMORANDUM FOR: JOHN B. MILES, JR.
Regional Administrator

THROUGH: LEO CAREY, Director
Office of Field Programs

FROM: PATRICIA K. CLARK, Director Designate
Directorate of Compliance Programs

SUBJECT: Blasters Circuit Testers

This is in response to your recent memo on the above subject and request for clarification as to the use of a blasters digital ohmmeter, No. 105, made by Thomas Instruments, Inc.

1926.906 states: (q) Blasters, when testing circuits to charged holes, shall use only blasting galvanometers equipped with a silver chloride cell especially designed for this purpose.

1910.109(e)(4) states: (vii) Blasters, when testing circuits to charged holes, shall use only blasting galvanometers designed for this purpose.

We agree with you that MSHA allows other instruments that are specifically designed for testing blasting circuits. Also, the OSHA 1910.109(e)(4)(vii) standard allows the use of a blasters digital ohmmeter that is designed for this purpose. After checking with MSHA's Approval and Certification Center, we find that this instrument is approved as a blasters digital ohmmeter. We understand the unit in question cannot produce or allow sufficient electric current (milliamps) to flow for ignition of any electric detonator manufactured by a member company of the Institute of Makers of Explosives.

We have also received a letter from Thomas Instrument, Inc., stating that their Model 105, blasters digital ohmmeter, is manufactured and assembled in strict accordance with drawings and specifications approved by 30 CFR Part 18, copy attached. Therefore, in our opinion it is safe to use the Model 105 blasters digital ohmmeter.

Please advise if we can be of further assistance.

Attachment