FLYROCK ISSUES IN BLASTING 

T. R. Rehak, T. S. Bajpayee, G. L. Mowrey, and D. K. Ingram 

ABSTRACT 

Blasting operations are an essential element in the recovery of our Nation’s mineral resources. The mining 

industry uses billions of pounds of explosives annually. The majority of blasting occurs in surface mining 

operations. Blasting results in the fragmentation and often the projection of rocks. Frequently, the rocks are 

thrown beyond the expected limits. Flyrock and failure to secure the blasting area dominate blasting-related 

accidents in mining, especially in surface mining. 

Blasting accidents in the mining industry tend to result in critical injuries or fatalities. Accident reports and 

information collected from the Mine Safety and Health Administration (MSHA) and other government 

agencies provide supporting evidence. According to the data collected, blasting-related accidents (in mining) 

were 11 times more severe than all other types of mining accidents. Blasting accidents are not unique to 

mining operations - the same situation exists in the construction field. 

In this paper the authors have compiled a list of the primary causes of flyrock and the failure to secure the 

blast area. In the next phase of this project, typical blasting scenarios will be reviewed which will highlight 

the main reasons flyrock and/or lack of blast area security occur. This will alert miners and construction 

workers to the current problems/hazards associated with blasting and to identify other safety measures to 

protect personnel. 
INTRODUCTION 

Annually, the United States uses billions of pounds of explosives in the mining and construction industries 

where rock fragmentation is an essential part of the project. A survey by the U.S. Geological Survey [2000] 

indicates that the United States used 2.12 million metric tons (Mt) of explosives in 1999. Mining operations 

and the construction industry accounted for the majority of the domestic explosive consumption. 

Even though blasting presents numerous hazards, these industries consider blasting to be essential for the 

success of their operations. A review of Mine Safety and Health Administration (MSHA) accident reports 

indicates that the mining industry has improved its blasting safety record during the past five years. Many 

factors contributed to this improvement, including: novel explosive formulations produced by explosive 

manufacturers; enhanced blaster’s training developed by academia, professional societies, and industry; 

and the meaningful roles played by local, state and federal agencies. 

An analysis by Siskind and Kopp [1995] indicated that lack of blast area security, flyrock, premature blasts, 

and misfires were the four major causes of blasting-related injuries in surface mining operations between 

1978-1993. During this period 356 injuries were attributed to surface blasting operations. Flyrock 

accounted for 28.3% of the injuries; lack of blast area security41.2%; premature blast 15.7%; misfires 7.8%; 

and all other causes 7%. During this period, 39 fatal injuries (2.4 per year) and 317 nonfatal injuries (an 

average of 19.8/year) were reported. Siskind’s study showed that, although blasting accidents declined from 

1990 to 1993, they continue to occur. Siskind used MSHA’s injury database as his primary source of 

information. 

The authors extended Siskind’s study to determine the current trend in blasting-related fatal and nonfatal 

injuries in surface mining. Between 1994 and 1997, six fatal injuries (an average of 1.5 per year) and 40 

nonfatal injuries (10 per year) were reported. During this 4-year period, flyrock and lack of blast area 

security accounted for 58.7% of all surface blasting injuries. 

Flyrock and lack of blast area security issues continue to pose problems for blasters. In 1999, three fatal 

injuries were attributed to blasting in surface mining operations. Flyrock and lack of blast area security 

issues accounted for two fatalities. This confirms the authors contention that problems associated with 

flyrock and lack of blast area security still exist. 

BLASTING INJURIES - MINING 

Tables 1 and 2 list fatal and nonfatal blasting injuries respectively from 1978 to 1998. These tables list 

injuries related to surface and underground mining for coal and metal/nonmetal (including stone, and sand 

and gravel) operations. A total of 104 fatalities occurred during the entire (1978-98) period, an average of 

five fatalities per year. Underground operations accounted for 56.7% of the fatalities; surface operations, 

43.3%. Coal mining accounted for 48% of the fatalities; metal/nonmetal, 52%. 

In table 1, the numbers within the parenthesis indicate four (4) year totals. Overall, fatalities have declined 

since 1978. However, fatalities involving surface mining operations in the metal/nonmetal sector have not 

changed substantially. 
Table 2 shows that a total of 1,008 nonfatal blasting injuries occurred between 1978-98, an average of 48 

injuries per year. Underground operations accounted for 63.6% of the nonfatal injuries; surface operations, 

36.4%. Coal mining accounted for 54.7% of the nonfatal injuries; metal/nonmetal, 45.3%. Again the 

numbers within the parenthesis indicate four (4) year totals. Note that nonfatal injuries related to coal 

mining have decreased significantly. 

However, injuries related to surface metal/nonmetal mining still persist. Twenty-six nonfatal injuries 

occurred between 1994-1997, while 33 nonfatal injuries occurred during 1981-1985 interval. In other words, 

no significant improvement has occurred in the 4-year injury rate in surface metal/nonmetal mining 

operations. 

These numbers are still of concern because of the severity of the injuries associated with explosives. The 

average days lost (ADL) involved in an explosive incident is much greater than the ADL associated with 

other classes of incidents in mining. An examination of accident statistics (1992-1996) provided in table A2 

of Phase I Strategic Planning document [NIOSH 1998] indicates that the ADL for explosive (all mining, all 

locations) incidents is 549.7 compared to an ADL of 46.4 for other (all mining, all locations, all class) 

incidents. This demonstrates the severe nature of the blasting incidents. The ADL caused by explosive 

incidents in surface stone mining operations was reported as 1524. This statistic emphasizes the need for 

more research into surface stone blasting procedures. 

FLYROCK AND BLAST AREA SECURITY - MINING 

Table 3 represents the contribution of flyrock and blast area security to the overall blasting scene. Out of 

1,112 blasting injuries (surface and underground combined), flyrock and blast area security accounted for 

281 injuries (25.3%). However, flyrock and blast area security issues represent 68.2% of all surface blasting 

injuries during the 1978-1998 time period. From table 3, it is apparent that the contribution of flyrock and 

blast area security ranged from 58.7% to 77.4% of all surface blasting injuries. Again, the data accentuates 

the need for continued research in these areas. 

BLASTING INJURIES - CONSTRUCTION 

- OSHA REVIEW 

A review of the Occupational Safety and Health Administration (OSHA) data was conducted as a means for 

determining the extent of flyrock accidents, injuries, and fatalities in non-mining blasting operations. The 

Code of Federal Regulations, OSHA citation history, and the OSHA Technical Manual on blasting or the 

use of explosives were examined. 

In reviewing the Code of Federal Regulations, which is a codification of the general and permanent rules 

published in the Federal Register by the Executive departments and agencies of the Federal government, it 

was determined that the flyrock concerns would best be identified under OSHA Code of Federal Regulations 

Title 29, part 1926: Safety and Health Regulations for Construction, subpart U: Blasting and the Use of 

Explosives, sections 1926.900 - 1926.914. However, in overview, the only standards which applies to either 

flyrock or blast area security are: 29CFR1926.909; 29CFR1910.109 (e)(1)(iii) and (iv); and 
29CFR1910.109 (e)(5). 

A thorough investigation was conducted of OSHA’s data base on issued citations and inspection reports for 

the time period of October 1997 through 1998. It was determined that flyrock is classified under North 

American Industry Classification System (NAICS) 1629, Division C: Construction, Major Group 16: Heavy 

Construction, Not Elsewhere Classified, Blasting except building demolition-contractors. In overview of 

the citations issued, there are four (4) citations standards that are related to blasting or use of explosives. 

During this period there were nine (9) citations issued with penalties totaling $4525.00. This dollar amount 

is relatively low and therefore, the authors assume that the citations were not issued for injuries or fatalities. 

OSHA’s Technical Manual provides technical information and guidance on occupational safety and health 

topics. However, there are no specific topics here which address the prevention of flyrock injuries or blast 

area limits. The sections that may address flyrock issues are generalized but do not specifically deal with 

flyrock. 

BUREAU OF LABOR STATISTICS 

The authors next reviewed the publically available yearly information provided by the U.S. Department of 

Labor, Bureau of Labor Statistics (BLS) on their web site at www.bls.gov. Note that the statistics include 

the private sector only and not government workers or those self-employed. Table R59 lists the number of 

nonfatal occupational injuries involving days away from work by source of injury and industry division. For 

the period from 1992 to 1997, there were a total of 422 nonfatal injuries in the construction industry 

(including transportation and public utilities) included in the category of “Explosives, blasting agents” or 

an average of approximately 84 per year. While the data does not appear to be consistently classified from 

year to year, this does indicate that workers are being injured in accidents involving explosives and blasting 

agents. The BLS data is not broken down sufficiently to determine what proportion of the explosive/blasting 

agent accidents are related to flyrock and blast area security. 

INTERNET/NEWSPAPER SEARCH 

Since OSHA’s Standards, citations history, and Safety Technical Manuals did not supply significant data 

and because of our concern with the reliability and the consistency of accident classification by BLS, we 

directed our attention to newspaper articles and to the internet. A Lexis-Nexis search was conducted for the 

period of 1994-1997 and the Institute of Makers of Explosives (IME) provided articles from their newspaper 

clipping service. The authors are currently in the process of reviewing 208 articles to determine if the 

accidents resulted from flyrock or blast area security issues. A sampling of articles related to the flyrock and 

blast area security issues in construction are briefly described below. 

1994, McGregor, TX “Explosion rocks local dealership” - A dynamite explosion to excavate a city 

sewer system lift station proved stronger than expected. Fortunately, despite the extensive damage 

done to the car body shop including breaking windows and damaging several vehicles, no one was 

injured. [McGregor Mirror, McGregor, TX] 
1995, Stuarts Draft, VA “Construction Worker Hurt in Blasting Accident Dies” A worker suffered 

a head injury when other workers were blasting at a Target Distribution Center construction project. 

A 10 to 15-pound rock propelled by the blast struck the worker who was then taken to an Intensive 

Care Unit via helicopter. He died the next day after undergoing surgery. Other workers said he ran 

for cover and was behind a van when the rock struck him, piercing his hard hat. [The Richmond 

Times Dispatch, Richmond, VA] 

1997, Antonia, MO “Blast Catapults Mud, Rocks into Buildings; State Revokes Road Construction 

Permit” An ammonium nitrate blast sent mud and rock flying for 600 feet on a road construction 

project on Highway M. It damaged four buildings and two cars. No one was injured. The blaster 

claimed the accident occurred because they hit a mud seam. A softball-sized rock was recovered 

after it crashed through the roof of a steel fabrication business. [St Louis Post-Dispatch, St. Louis, 

MO] 

1998, Douglasville, GA “Judge Halts Blasting at Arbor Place Mall” The blasting contractor was 

excavating rock at a construction site of a new mall, when a blast sent debris flying, damaging 

several homes. The company was fined $7500 and required to provide more safety measures. [The 

Atlanta Journal and Constitution, Atlanta, GA] 

1999, Brentwood, TN “Explosion at Construction Site Damages Homes” Workers were setting off 

dynamite to lay a sewer line. A piece of rock fell through the roof of a home of a 72-year-old man 

who was at home with his wife and daughter. Several other homes were also damaged. Fortunately 

no one was hurt. [Associated Press] 

1999, Braintree, MA “Hitting too Close to Home - Rocks from Blasting Rattle Neighbors” Blasting 

was being done at a cemetery to create more space for graves. Some rocks from the blast flew nearly 

800 feet, reaching some private property near the cemetery. A rock, the size of a softball, struck the 

roof of one of the neighbors’ houses. No one was injured. [Patriot Ledger Quincy, MA] 

It is plainly evident that the construction industry does not have as detailed and accurate reporting system 

in place compared with the Mine Safety and Health Administration (MSHA) for the mining industry. 

However, it appears that flyrock and blast area security problems exists in both industries. 

FLYROCK 

The U. S. Code of Federal Regulations [CFR], Title 30 defines ‘Blast Area’ as the area in which concussion 

(shock wave), flying material, or gases from an explosion may cause injury to persons. The CFR also states 

that the blast area shall be determined by considering these factors: 

(1) Geology or material to be blasted, 

(2) Blast pattern, 

(3) Burden, depth, diameter, and angle of the holes, 

(4) Blasting experience of the mine personnel, 

(5) Delay systems, powder factor, and pounds per delay, 

(6) Type and amount of explosive material, 
(7) Type and amount of stemming. 

Flyrock is generally perceived as the rock propelled beyond the blast area. IME [1997] has defined flyrock 

as the rock(s) propelled from the blast area by the force of an explosion. 

PRIMARY CAUSES OF FLYROCK 

Generally, flyrock is caused by a mismatch of the explosive energy with the geomechanical strength of the 

rock mass surrounding the explosive charge. Factors responsible for this mismatch include: 

- Abrupt decrease in rock resistance due to joint systems, bedding layers, fracture planes, geological 

faults, mud seams, voids, localized weakness of rock mass, etc. 

- High explosive concentration leading to localized high energy density, 

- Inadequate delay between the holes in the same row, or between the rows, 

- Inappropriate blast design, 

- Deviation of blast holes from its intended directions, 

- Improper loading and firing practice, including secondary blasting of boulders and toe holes. 

a) BURDEN: Insufficient burden is a primary cause of flyrock from a highwall face. Highwall faces are 

irregular and therefore do not provide uniform burden from each point of the loaded borehole. Following 

the laws of physics, high-pressure gases generated during blasting will vent out and therefore pose the 

greatest hazards at the weakest point in the highwall. Blasters need to visually examine or laser profile the 

highwall face and search for zones of weakness, backbreak, concavity, unusual jointing and overhang. 

b) BLAST HOLE LAYOUT AND LOADING: Any deviation in the direction of a blast hole can reduce or 

increase the burden. This becomes a significant factor for deep holes. A slight deviation from vertical toward 

the highwall can drastically reduce the burden at the bottom of the hole. 

Blasters must prime and load their holes as planned. While loading a hole, blasters must frequently check 

the rise of the powder column to prevent overloading due to the loss of powder in voids, cracks, or other 

unknown reservoirs. Such overloading will generate excessive release of energy. 

c) GEOLOGY AND ROCK STRUCTURE: Sudden change in geology or rock structure can cause a 

mismatch between the explosive energy and the resistance of the rock. It is prudent to try to detect such 

changes in advance and adjust accordingly. Sedimentary rocks often change their geomechanical properties 

due to abrupt changes in the direction of laminations or bedding planes, inclusion of zones of weakness, and 

voids. Geological intrusions can compromise the strength of the parent rock. Presence of mud seams, voids, 

caverns should cause a concern for the blaster. Inadvertently loading these areas will produce a high energy 

concentration. 

d) STEMMING: Stemming provides confinement and prevents the escape of high-pressure gases from the 

borehole. The stemming should provide resistance to the escape of high-pressure gases comparable for that 

of the burden. Konya and Walter [1990] recommend a stemming length of about 0.7 times the burden. 

Improper or inadequate stemming can result in stemming ejections. Insufficient stemming also causes 

violent fragmentation of the collar zone resulting in flyrock and airblast. 
e) DETONATOR FIRING DELAY: Critical elements of any blast design are firing delays between adjacent 

holes in a row and also those between successive rows. The firing delay is a function of the burden, spacing, 

hole depth, rock type, and the quantity of charge fired per delay. Proper firing delay helps to achieve good 

fragmentation of the blasted material. It also reduces ground vibration, air blast, and flyrock. The rock 

fragmented by the previous hole must be given a chance to move out prior to firing subsequent holes 

f) LACK OF BLAST AREA SECURITY: An analysis of blasting injuries indicates that several factors are 

involved in causing injuries due to lack of blast area security. These factors are: (a) failure to evacuate the 

blast area by employees and visitors; (b) failure to understand the instructions of the blaster or supervisors; 

(c) inadequate guarding of the access roads leading to the blast area, or the secured area; (d) taking shelter 

at an unsafe location, or inside a weak structure. Blast area security issues could be addressed by providing 

adequate training and refresher courses (class room and hands-on type) to the blaster and other involved 

employees. 

CONCLUSIONS 

1. Domestic consumption of explosives has grown considerably in the recent years. Surface blasting 

operations related to recovery of coal, minerals, and construction activity account for a major part of this 

consumption. Even though blasting presents numerous hazards, the mining and construction industries 

consider blasting as an essential ingredient for the success of their operation. Injury analysis indicates that 

lack of blast area security and flyrock account for the majority of blasting-related injuries in surface mining 

operations. This calls for strengthening of training activities. 

2. The ADL (average days lost) due to an explosive incident is much greater than the ADL caused by other 

class of incidents. An examination of accident statistics reveals that the ADL for explosive (all mining, all 

locations) incidents is 549.7 compared to an ADL of 46.4 for all other (all mining, all locations, all classes) 

incidents. This demonstrates the severe nature of the blasting accidents. The ADL caused by explosive 

incidents in surface stone mining operations was reported as 1524. The authors recommend more research 

emphasis on surface stone blasting operations. 

3. Blast area has been defined as the area in which concussion (shock wave), flying material, or gases from 

an explosion may cause injury to persons. The blast area shall be determined by considering these factors: 

geology or material to be blasted; blast pattern; burden; depth, diameter, and angle of the holes; blasting 

experience of the mine; delay systems, powder factor, and pounds per delay; type and amount of explosive 

material; type and amount of stemming. These factors should be addressed in training session for blasters. 

4. The rock mass surrounding the borehole experiences a very high degree of mechanical stress from the 

products of detonation. Any irregularity in the geological structure or confinement will cause an uneven 

stress field which may result in flyrock. Development of excessive or disproportionate gas pressure may 

propel rocks a great distance. Geological anomalies and lack of proper confinement are considered 

contributory factors for the creation of flyrock. The techniques to predict anomalies or compensate for its 

effects in blast design merit further study. 

5. The factors involved in causing injuries due to lack of blast area security are: (a) failure to evacuate the 
blast area by employees and visitors; (b) failure to understand the instructions of the blaster or supervisors; 

(c) inadequate guarding of the access roads leading to the blast area, or the secured area; (d) taking shelter 

at an unsafe location, or inside a weak structure. These accidents are preventable with good training and 

communications. 

REFERENCES 

Siskind DE, Kopp JW [1995]. Blasting accidents in mines: a 16-year summary. In: Proceedings of the 21st 

Annual Conference on Explosives and Blasting Technique. Cleveland, OH: International Society of 

Explosives Engineers, pp. 224-239. 

NIOSH [1998]. Phase I Strategic Planning, FY 98. Office for Mine Safety and Health Research, Pittsburgh 

Research Laboratory, Spokane Research Laboratory: U.S. Department of Health and Human Services, Public 

Health Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and 

Health, Table A2, pp. 12. 

CFR. Code of Federal Regulations. Washington, DC: Government Printing Office, Office of the Federal 

Register. 

Flinchum R, Rapp D [1993]. Reduction of air blast and flyrock. In: Proceedings of the Nineteenth Annual 

Conference on Explosives and Blasting Technique. Cleveland, OH: International Society of Explosives 

Engineers, pp. 147-157. 

Fletcher LR, D’Andrea DV [1986]. Control of flyrock in blasting. In: Proceedings of the Twelfth Annual 

Conference on Explosives and Blasting Technique. Cleveland, OH: International Society of Explosives 

Engineers, pp. 167-177. 

IME [1997]. Glossary of Commercial Explosives Industry Terms. Safety Publication No. 12, Institute of 

Makers of Explosives, 1120 Nineteenth Street, NW, Suite 310, Washington, D.C. 20036-3605, pp. 16. 

USGS [2000]. Mineral Industry Surveys, Explosives, 1999 Annual Review, U. S. Geological Survey, 983 

National Center, Reston, VA 20192, August, 2000, by Debra A. Kramer, Explosive Commodity Specialist. 

Konya CJ, Walter EJ [1990]. Surface blast design. Prentice Hall Inc. (a division of Simon & Shuster Inc.), 

Englewood Cliffs, New Jersey 07632, 303 pp. 
Table 1. Fatal blasting injuries, 1978-98 

Year 

Coal 

Underground Surface 

Metal/nonmetal 

Underground Surface 

Total 4-year 

average 

1978 3 0 5 2 10 11.25 

1979 0 2 5 0 7 

1980 7 1 5 2 15 

1981 3(13)1 2 (5) 5 (20) 3 (7) 13 

1982 3 1 2 2 8 5.00 

1983 0 0 0 0 0 

1984 1 1 1 3 6 

1985 6 (10) 0 (2) 0 (3) 0 (5) 6 

1986 0 3 1 0 4 3.25 

1987 0 1 0 0 1 

1988 2 0 0 0 2 

1989 0 (2) 2 (6) 1 (2) 3 (3) 6 

1990 3 2 0 3 8 4.75 

1991 2 1 2 0 5 

1992 0 1 0 3 4 

1993 0 (5) 1 (5) 1 (3) 0 (6) 2 

1994 0 1 0 2 3 1.75 

1995 0 0 0 1 1 

1996 0 0 0 1 1 

1997 1 (1) 0 (1) 0 (0) 1 (5) 2 

1998 0 0 0 0 0 — 

Total 31 19 28 26 104 —

Average 1.5 0.9 1.3 1.2 5.0 — 

 Numbers within the parenthesis indicate 4 years totals

 Source: Siskind and Kopp [1995] and MSHA Database 

1
Table 2. Nonfatal blasting injuries, 1978-98 

Year 

Coal 

Underground Surface 

Metal/nonmetal 

Underground Surface 

Total 4-year 

average 

1978 51 19 39 21 130 107 

1979 49 14 34 12 109 

1980 48 14 33 16 111 

1981 28 (176)1 10 (57) 32 (138) 8 (57) 78 

1982 19 5 9 6 39 45.5 

1983 17 7 10 5 39 

1984 16 16 4 18 54 

1985 32 (84) 3 (31) 11 (34) 4 (33) 50 

1986 17 9 9 8 43 50.5 

1987 22 9 9 14 54 

1988 21 11 13 9 54 

1989 15 (75) 13 (42) 12 (43) 11(42) 51 

1990 13 6 6 13 38 27 

1991 9 5 5 11 30 

1992 2 8 6 3 19 

1993 10 (34) 2 (21) 2 (19) 7 (34) 21 

1994 5 7 2 8 22 18 

1995 1 2 4 7 14 

1996 4 4 6 6 20 

1997 1 (11) 1 (14) 9 (21) 5 (26) 16 

1998 4 2 2 8 16 — 

Total 384 167 257 200 1,008 — 

Average 18.3 8.0 12.2 9.5 48.0 — 1

 Numbers within the parenthesis indicate 4 year totals

 Source: Siskind and Kopp [1995] and MSHA Database 
Table 3. Trends in flyrock injuries (surface mining), 1978-98 

Activity or cause 

Fatal plus nonfatal injuries 

1978-81 1982-85 1986-89 1990-93 1994-97 1998 Total 

Blast area security 51 28 43 25 17 3 167 

Flyrock projected beyond blast 26 22 29 24 10 3 114 

area 

Total of above 77 50 72 49 27 6 281 

Total of above (as a percent of 61.1 70.4 77.4 74.2 58.7 60 68.2 

all surface blasting injuries) 

Total of above (as a percent of 16.3 24.8 33.5 38.6 34.2 37.5 25.3 

all blasting injuries) 

All surface blasting injuries 126 71 93 66 46 10 412 

All blasting injuries 473 202 215 127 79 16 1,112 

Source: Siskind and Kopp [1995] and MSHA Database