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Western District
Metal and Nonmetal Mine Safety and Health


National Quarries, ID No. 04-00204
National Quarries
San Marcos, San Diego County, California

October 6, 1995


Dennis D. Harsh
Mine Safety and Health Inspector

Arnold E. Pederson
Mine Safety and Health Inspector

Western District Office
3333 Vaca Valley Parkway, Suite 600
Vacaville, California 95688
Fred M. Hansen
District Manager


Lawrence Dyer, quarryman and laborer, age 44, was fatally injured October 6, 1995 at approximately 2:00 p.m., while drilling plug holes in a block of granite. He accidentally drilled into a misfired hole. Dyer had a total of eight months of mining experience, all at this operation.

The MSHA Western District Office, Vacaville, California, was notified of the accident by a telephone call to the answering service at approximately 4:57 p.m., October 6. The call was made by Margaret Johnson, wife of a National Quarries co-owner. An investigation was begun on October 7. The accident site was secured by an MSHA inspector prior to the investigation.

National Quarries was a single bench, open pit granite quarry with an adjacent mill. The mine was originally developed by Emil Johnson and Sons in the early 1920's. The operation was located at San Marcos, San Diego County, California.

The mine, which employed nine people, operated one eight hour shift per day, five days a week. Mining was accomplished by drilling and percussion blasting. Black powder was used to split the granite into blocks. The blocks were then transported to the mill where they were cut, sized, polished, and delivered to customers.

Principal officials at this operation were:

Gary N. Johnson, co-owner
Michael G. Johnson, co-owner

Information for this report was obtained by interviewing company officials and employees and by conducting an on-site investigation.

The last regular inspection was made on May 17 and 18, 1995.


About two weeks prior to the accident, a 1 1/2 inch by 3 foot 8 inch bore hole was drilled into a granite block at the quarry. The bottom of the hole was plugged with 2 3/4 inches of clay stemming and an electric blasting cap was inserted.

Approximately 4/10 pound of black powder was poured into the hole, which was then filled with stemming. The charge failed to detonate so the foreman decided to refire it rather than wash out the blasthole. He thought the second attempt was successful.

Explosives and equipment being utilized:

Black powder - Type a explosive, granulation 3FA, GOEX, INC.

Detonator - E.T.I. (formerly DuPont) 500 MS #14 Delay Blasting.

Blasting Machine - Fidelity Electric Co., Inc., Model 50, SN 503-41WF.

Galvanometer - Uni-Therm with silver chloride battery (Not in operating condition).

Gardner Denver pneumatic rotary/hammer drill - Used with drill steel, of varyious lengths, and scarring reamer bits to prepare granite blocks for explosive charges. The block with the undetonated charge had been drilled two weeks earlier.

Atlas Copco hand held rotary pneumatic drill, Model BBD 12 T, SN NACO3146A - Used to drill plug holes in the granite block.

7/8 X 14 and 3/4 X 13 inch drill bits were used to drill 6 inch deep holes that were spaced about 3 inches apart along the block.

A steel wedge was hammered between two other long steel wedges that had been placed in the hole to spall, or break, the block.

LeRoi, model 170, compressor. Supplied air, regulated at 80 psi, to the drill. Coupled 3/4 and 1/2 inch air hoses connected the compressor to the drill. To drill a horizontal hole in the face, the operator would have to stand behind the drill and lean, or push, against it.


Lawrence Dyer reported for work at his regular 8:00 a.m. starting time, October 6, 1995. Antonio Rojano, foreman, assigned Dyer and Rafael Escobedo, laborer, various work activities including; fueling equipment, drilling large granite blocks that were to be broken down into smaller sizes, and then making room for them by cleaning up the area. Granite blocks were then prepared for removal to the work platform.

At about 12:45 p.m., following lunch and a safety meeting, a mill worker, Dan Grey, arrived at the worksite to transport a granite block to the mill for sawing. About 1:00 p.m., Dyer and Escobedo placed chains on the granite block Grey had selected. During removal it was noticed that the block had an irregular shape.

Rojano instructed Dyer to drill plug holes in it for trimming. Dyer drilled two plug holes and as he was drilling the third, at about 2:00 p.m., the drill steel intersected a charged blast hole causing it to detonate.

In the meantime, Rojano and Escobedo had gone to the quarry to load previously drilled holes. On hearing the explosion they returned to Dyer's location. There they found him lying on the ground seriously injured. Escobedo remained with Dyer while Rojano went to the mill to call for assistance. Rojano then drove to the front gate so he could direct emergency units to the accident site. Paramedics arrived about 2:10 p.m., followed by a life flight crew at about 2:20 p.m. They attempted to stabilize Dyer for transportation. At about 2:50 p.m. he was pronounced dead at the scene by Georgeanne Abbott, a registered nurse. The body was then transported, by Balboa Transport Service, to the medical examiner's office where an autopsy was performed by Dr. Blackbourne.


The accident occurred because a misfire was handled improperly. Steps were not taken to determine the cause of the misfire and to assure that the explosive potential had been eliminated.

Lack of maintenence of blasting instruments added to the risk of handling explosives.


103(k) Order No. 4143276, issued October 7, 1995.

An unplanned detonation of an explosive charge occurred at the quarry. One quarryman was fatally injured as he attempted to drill a hole to break dimensional stone. This order prohibited any further drilling, blasting, or any alteration of the accident site pending an investigation by MSHA to determine if additional unexploded explosives remained in the quarry.

104(d)(1) Citation No. 4342239, Section 56.6407(a), Issued October 9, 1995.

Antonio Rojano, foreman and licensed blaster, does not use a galvanometer or other approved blasing instrument to test the continuity of each detonator in blast holes prior to stemming and connecting the detonators to the blasting line. This is an unwarrantable failure.

104(d)(1) Order No. 4342240, Section 56.6407(d), Issued October 9, 1995. 30 CFR 56.6407(d).

Antonio Rojano, foreman and licensed blaster does not use an approved blasting instrument or galvanometer to test the total electrical blasting circuit resistance before making connections to the power source, a magneto plunger. This is an unwarrantable failure.

104(d)(1) Order No. 4342241, Section 56.14100(b), Issued October 9, 1995.

The blasting galvanometer was not being maintained in an operable condition due to a dead battery within the instrument. This defect could result in a false indication of blasting components which could cause an accident resulting in serious injuries.

September 28 and October 5, 1995 notations on a calendar, used as a maintenance log, indicated that the instrument needed a new battery. This is an unwarrantable failure.

104(d)(1), Order No. 4342242, Section 56.6900(e), Issued October 9, 1995.

The foreman and licensed blaster failed to recognize a misfired hole, or follow proper procedures for handling a misfire. The misfired contents had not been disposed of by washing the stemming and charge from the hole in accordance with requirements for damaged explosives. This is an unwarrantable failure.

Respectfully submitted by:

/s/ Dennis D. Harsh
Mine Safety and Health Inspector

/s/ Arnold E. Pederson
Mine Safety and Health Inspector

Approved by:

Fred M. Hansen, Manager
Western District
Related Fatal Alert Bulletin:
Fatal Alert Bulletin Icon [FAB95M37]