Chapter 31: Blast Planning
Blast design is an ever changing process for which success or failure depends on its outcome. The designer has to determine or adjust a number of controllable parameters to achieve a certain objective. In the process, the designer has to consider several uncontrollable parameters (geology and structure, presence of water etc.), which must be quantified in order to predict the results of the blast.
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A written blast plan specifies any additional protective measures necessary to protect major or historical structures. Also include a description of any monitoring equipment such as seismographs and video cameras that may be available for use.
While many components of a blast plan are site-specific, some companies may opt for addressing some items such as warning signals and notifications in a standard operating procedure (SOP, or SCOP) rather than including policies that apply universally to the workforce and project. Some additional regulations require blast plans and have specific detail that must be included.
The blast plan is not a treatise on worker safety. All workforce personnel should have already been trained and prequalified to conduct the blasting activity in a safe handling of explosives products and their use.
Finally, the blast plan should discuss the lines of communication at the project site for project problems, site security and emergencies situations. Explosives security and emergency action plans are prudent business practices and often required by local regulations. A sound plan will ensure that management personnel know the nature of the activity, where explosives are to be stored and whom to contact for routine and emergency situations.
Lines of Communication
Clear lines of communication within and throughout the project area are necessary to ensure project success. The blast plan should list all the companies and regulatory authorities associated with the project. Clear lines of communication will also show the public that the operation is prepared to work in a well-defined, open manner.
The blast plan should contain a list of the names and telephone numbers of all responsible parties to the blasting activity. This listing will facilitate upstream or downstream communication along the chain of command and allow the blaster to rapidly identify responsible parties in the face of the public. Potential parties to be listed by name, affiliation and phone number include but may not be limited to those listed in table 31.2. With these contacts in hand the blaster can usually contact any party for routine business or an emergency.
Potential Parties To Be Listed in the Blast Plan
Table 31.2 – Potential parties to be listed in the blast plan.
Blasting Maps
The spatial relationships between the blasting and nearby features are critical for developing a sound blast plan. Most projects have maps that denote the potential blasting areas, typical geology and nearby man-made structures that must be protected from vibrations and flying debris. If maps are not readily available, topographic maps and/or aerial photographs should be used to determine the spatial relationships. Topographic maps and aerial photographs are readily available at number of internet sites. A blasting map will allow the blaster to delineate all the potential blast sites, decide on the needed equipment and begin to develop a site security plan to ensure worker and public safety. It should also extend out to at least one km (2/3 mile) from the project/permit boundary. Not all blasting maps remain accurate, as new structures may move onto the area over time. Furthermore, the blaster, contractor, or project engineer should regularly check to ensure the accuracy of the maps provided to them. A visual drive through of the area is a good best practice. Another good practice is to use latitude and longitude grids on the blast map, since most blasters use some type of a handheld global positioning system (GPS) to determine the location of the blast site.
Each project will have numerous blast sites over the duration. The location of blasting in nearby public and private structures will strongly impact the equipment needs, explosives selection and blast design. The blaster will make continual reference to the maps once blasting begins. The blaster should secure an area sufficient to protect the public and property based on the location of blasting within the permit boundary, the type of blasting being conducted and type of material being fragmented. The blast area is not necessarily confined to the project/permit boundary.
Geologic Conditions
The project designer or project engineer should have already described the geology of the area in detail. The blast plan should include a general description of the type and depth of rock to be excavated for use by the blaster in the field. This information will allow the blaster to develop a mental idea of the project before arriving at the site and decide on the equipment and explosives necessary for the project.
For construction projects the depth of excavation and any benching requirement for slope stability should be discussed. For mining projects the type of ore body should be described along with the excavation depth. For a coal mine, the depth and rock type to each coal seam should be described.
Most importantly the plan needs to discuss the existence of any known geologic anomalies, which may include those listed in table 31.3.
Geologic Anomalies To Be Discussed
Table 31.3 – Geologic anomalies to be discussed.
The rock conditions are very important to the blaster and a means of communication between the driller and blaster should be established on all blasts to determine the geologic conditions before the loading process begins. Chapter 8 discusses many of the geologic considerations necessary.
Safety Procedures
The on-site safety procedures may be discussed specifically for each project or may be part of a company's standard operating procedures. Overall procedures should be part of the SOP instead of the site-specific blast plan. But if unique circumstances exist, such as hot bore holes, then the handling and loading procedures should be discussed. In heavily populated areas or near roadways, particular attention should be paid to the potential for flyrock, fumes and concussion. The plan should discuss the hazard potential and actions that the blaster may take to reduce the hazards.
Explosives Storage and Security
An appendix to the blast plan should identify the responsible parties and show the storage area on the blasting map. If explosives are to be delivered daily, then the plan should discuss the daytime security measures. Again, many companies have SOPs to address this issue and need not be elaborated in the blast plan unless minimal site conditions exist.
Permits and Licenses
An appendix to the blast plan should contain all the necessary permits and licenses from local government agencies. Often the project manager or superintendent obtains these. Each needs to be read closely for special conditions and enumerated in the body of the blast plan.
Sometimes special blasting approvals are needed that are unknown to the project manager, but are known to the blaster. For example, in the U.S. when blasting within 500 feet of active underground mines, the Federal and State agencies responsible for the health and safety of underground miners must approve the blast plan. The U.S. Mine Safety and Health Administration (MSHA) is the responsible Federal agency in every state but some states may have their own agency on health and safety of miners or other workers.
Anticipated Designs
The basic objective of an anticipated blast design (ABD) is to give details on the first blast to be conducted at a project or at some point. Quite often this design will reflect the design on which the project bid was based. Anticipated designs, instead of standard or typical, allow blasters the flexibility to change the design based on unexpected conditions encountered at project site once excavation has begun. Trying to anticipate all field and rock conditions is nearly impossible since many may not be defined or be discovered until after the project has commenced. In these specific cases, the blaster needs flexibility to modify blast designs daily based on the site conditions encountered. Specifically the ABD provides a record of the anticipated blast designs before a blast occurs.
If different types of blasting are proposed within the project/permit, the blast plan should describe and provide a specific ABD for each scenario. Examples of different types of blasting that could occur at the same site are listed in table 31.4.
Possible Types of Blasting Within a Project/Permit Area
Table 31.4 – Possible different types of blasting within a project/permit.
The design should be the blaster's best estimate of the first blast for the project areas. Considerations must be given to geology, density of the rock, depth of borehole, explosives density and borehole diameter, spatial relationships, building types, type of blasting, fragmentation needs, nearby homes, and active or abandoned underground mines. Specific precautions and conservative designs are necessary in situations where flyrock, ground vibrations, and overpressures pose a threat to residents, miners and property. When blasting near homes an ABD should consider safety precautions necessary to minimize any adverse effects.
Factors To Be Listed in the Blast Plan
Table 31.5 – Factors to be listed in the blast plan.
The ABD will ensure that the blasting meets the needs of the project and the performance standards of the project or regulations.
Blast Initiation and Post Blast Assessment
The blast plan should contain a short description of the blaster's location at the time of the blast and how contact will be maintained with others responsible for blast area security (See chapters 1 and 10). Once initiated the blaster must check the site for misfires and performance (See chapters 16 and 32). If a blasting company has SOPs for this part of the blasting, elaborations here is probably not necessary.
Control of Adverse Effects
Blasting generates five types of adverse effects: (1) flyrock, (2) ground vibrations, (3) air overpressure, (4) fumes and (5) dust. Each blast must be designed to ensure worker and public safety both inside and outside the project permit area. Furthermore, the blasting must be conducted in a manner to prevent damage to property outside the project/permit area or equipment inside the project area.
The blast plan should identify the vibration limits at all nearby structures and how blasts will be monitored to ensure compliance with the plan. For flyrock, dust and fumes the potential travel distances should be determined.
Monitoring Plans
The blast plan should contain a description of any monitoring system to evaluate the factors listed in table 31.6. This includes the type, capability, and sensitivity of any blast monitoring equipment, the proposed procedures and the proposed locations of monitoring. The locations of all blast monitoring should be discussed and specified on the blasting map. Quite often the spatial relationship and atmospheric conditions of a blast site warrant monitoring at a multitude of locations.
Plan Factors and Monitoring Methods
Table 31.6 – Monitoring plan factors.
The blaster, the general contractor, or a consulting company is responsible for obtaining the equipment for field use and deploying the equipment in the field at the proper locations to determine the level of adverse effects from any blast.
Ground Vibration Limits
All blasts generate ground vibrations unless the blast is an open-air detonation. Numerical ground vibration limits must be specified in the blast plan for every nonexcepted man-made structure near the project/permit area. Numerical limits may be based on regulatory limits, project specification limits, or blaster set limits for liability protection. Most regulatory limits apply to dwellings, public buildings, schools, churches, community buildings or institutional buildings. For other types of structures such as, historic or unique structures, engineered structures (roads, bridges, etc.), utilities (including water towers, telephone poles, pipelines, etc.), tunnels, dams, impoundments, and underground man-made the vibration limits must be specified in the blast plan based on the scientific literature. Appropriate limits are discussed in chapter 26.
Occasionally ground vibration limits must be set to limit annoyance when sensitive structures or people are nearby. Sensitive structures include hospitals, medical facilities or doctors' offices where any low level vibration event may be disruptive to medical procedures. Sensitive people are sometimes special needs people that startle easily and may become a danger to themselves or their caretakers. Most local regulations do not require care in these areas but prudent public relations practices are a good business practice.
Air Overpressure Limits
All blasts will generate air vibrations unless the blast is completely confined. Numerical air overpressure limits must be specified for each man-made structure near the project/permit in the blast plan. However, unlike ground vibrations, air overpressure limits are not necessary for below ground man-made structures. Numerical limits may be based on regulatory limits, project specification limits, or blaster set limits for liability protection. Most regulatory limits apply to dwellings, public buildings, schools, churches, community buildings or institutional buildings. For other types of structures, such as historic or unique structures, engineered structures (roads, bridges, etc.), and utilities (including water towers, telephone poles, etc.) the overpressure limits must be specified in the blast plan based on the scientific literature. The appropriate limits are discussed in chapter 26.
Occasionally air overpressure limits must be set to limit annoyance when sensitive structures or people are nearby. Sensitive structures include hospitals, medical facilities or doctors' offices where any low level vibration event may be disruptive to medical procedures. Sensitive people are sometimes special needs people that startle easily and may become a danger to themselves other special needs people of their caretakers. Most local regulations do not require care in these areas but prudent public relations practices are a good business practice.
Flyrock
Flyrock is very dependent on site conditions and blasting methodology. The blaster is responsible for the performance of each blast based on the site-specific characteristics. The blast plan should describe how flyrock will be controlled through prudent blast designs and monitored to meet the desired goals (See chapter 15). Flyrock should never travel beyond the project/permit area. When it does, injury to people and damage to property are likely.
Monitoring is generally conducted by a post blast inspection of the area for rocks off the site, tree damage or, in the worst case, damage to nearby property. The blast plan should describe the blaster's flyrock inspection protocols after each blast. Unfortunately this type of assessment does not allow the blaster to clearly identify the problem area and take corrective action.
Video recordings will provide the best information for post blast assessment. A well-placed camera will provide a view of the top of the blast and any free faces. By seeing all free faces the blaster can determine the origin of the flyrock and make design adjustment or address field implementation issues.
Dust
Each blast will generate dust in differing quantities depending on the confined nature of the blast and the rock characteristics. Blasting dust is more of an annoyance to people than a health threat. Nearby residents will become strongly annoyed when dust routinely covers cars, homes, laundry or enters the household through open windows.
When dust is a concern, a blast plan should address any monitoring or control methods. Dust control methods would include modified blasting techniques, adding water to the blast site, water, etc. Limiting blasting to favorable wind directions days is a secondary form of dust control. Some of these techniques are better for small blasts as opposed to very large blasts.
Dust monitoring is not very common but may be conducted with video or dust monitors. Mostly the need is to document the directional effects of the dust cloud to show that the mitigation techniques are either not generating dust or are directing the dust away from areas of concern.
Fumes
Fumes are generated from each blast and, if allowed to accumulate in confined spaces can become dangerous to workers or nearby residents. For underground blasting, the blast plan should specify the time interval before workers can reenter the work area based on the ventilation network of the excavation.
For surface blasting, fumes are most likely to accumulate in confined places like basements or manholes when blasting is near structures and the blasting is conducted with high confinement to restrict flyrock. In these cases carbon monoxide is the most likely dangerous gas. The blast plan should discuss mitigation techniques such as rapid excavation of blasted material or early warning devices in the nearby confined spaces to identify elevated levels of carbon monoxide. For residential applications, carbon monoxide monitors are readily available at hardware stores for a reasonable cost and can be left with the homeowner after blasting as a public relations gesture.
Occasionally plumes of orange-brown gas (oxides of nitrogen) are generated from surface blasting activities. Unlike carbon monoxide, oxides of nitrogen are visible and can be monitored with a video camera. Any visible gas from a blast should be avoided. Like dust, limiting blasting to favorable wind direction days is a secondary form of gas control. Gas generation and control techniques are discussed in chapter 28.
Preblast Surveys
A preblast survey (PBS) documents the existing condition of a structure prior to blasting. A PBS is offered free-of-charge to each resident or owner of a dwelling or structure near the project/permit area. In addition, the survey should identify any unique conditions or contents of structures that might warrant special protection. The PBS provides liability protection for the blaster and is a public relations opportunity for the project.
The blast plan should identify the area of coverage for PBSs and clearly state that all PBSs will be complete before any blasting begins. The areal extent of the offering should be based on the expected vibration levels. At a minimum, PBSs should be offered in an area where ground vibration levels over 12.5 millimeters/second (0.5 inches/second) or air overpressure levels of 133 decibels are expected. Some contract specifications or regulatory authorities specify a minimum distance regardless for the blast design parameters. The aerial extent should be shown on the blasting map.
Blasting Schedule And Warnings
Each blast plan should contain a blasting schedule and specify the warning signals to be used at the site. By specifying the warning signals, all on-site workers will also be warned on a daily basis of an impending blast. The schedules will allow the public to be prepared for the activity and the warning signal provides daily notification of each impending blast.
All routine blasting should be scheduled during daylight hours unless unusual conditions warrant nighttime blasting. Nighttime blasting is very disruptive to the public and creates site security challenges.
For small projects, schedule and warning notifications may be spoken or posted on door hangers on and around the site. For large projects, the schedule may be published in a local newspaper, posted on a website, and transmitted on a social media platform(s). Reportable quantities vary from state to state in the U.S.
Signage, Blast Area Security And Access Control
Blast area security is critical to provide protection to the public. Signs alert people to the location of the potential hazard and describe the warning signals of impending blasts. The blast plan should contain the proposed wording on site blasting signs to be posted at those access points and along project/permit boundaries. Sign wording should describe the warning signals and time interval associated with each. Lastly the blast plan needs to discuss blast area access control, who is in charge and how the area will be deemed safe.
Records Of Blasting Materials
A record of each blast must be kept as discussed in chapter 27. The blast plan should contain a blank blast log that has all the required elements. The blast log should prompt the blaster to the minimum information needed to meet regulatory requirements, contractual specifications, and provide maximum liability protection. Simply, the record should allow another blaster to recreate the blast in space, time and character for post blast assessment or document the disposition of explosives for tracking purposes. Once part of the plan, the blaster is expected to use the form in following blasts.
The most critical elements of the blast log for adverse effects control are the blast location, distance to the nearest structure and the maximum charge weight per delay. These allow post blast assessment of vibration data and extrapolation of vibration data to places without measurement information. Any and all blast vibration monitoring or drill log anomalies results should also be part of the blast log and be in conformance with the plan.
Emergency Action Plans
Each blast site should have an emergency action plan for site-specific conditions. Some of the minimal plans should include the three elements listed in table 31.7.
Minimum Emergency Action Plan Elements
Table 31.7 – Minimum emergency action plan elements.
SUMMARY
A blast plan in the blaster's guide for day-to-day operations at a specific project. A good plan will facilitate excavation, minimize costs, promote communications and maintain/improve public relations. But more importantly the plan must be concise. Too much verbiage and scores of paper will not be implemented in the field.
For long term projects the blast plan should be periodically amended or updated based on changing field conditions, project requirements and/or regulatory requirements. If at any time blaster is assigned to a project, a current blast plan should facilitate a smooth transition. Try to address many of the routine procedures in a standard operation procedure (SOP) manual. The blast plan should only cover the site-specific aspects of the blasting. Make the plan, keep it simple, and work the plan.
ADDITIONAL RESOURCES
Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF). Code of Federal Regulations (CFR), title 27, ATF, Washington, D.C.
Department of Transportation (DOT). Federal Motor Carrier Safety Administration (FMCSA). Code of Federal Regulations (CFR), title 49. DOT, Washington, D.C.
Institute of Makers of Explosives (IME). Safety Library Publications (SLP). IME, Washington D.C.
International Society of Explosives Engineers (ISEE). 1998. ISEE Blasters' Handbook™, 17th Edition ISEE, Cleveland, OH.
Mine Safety And Health Administration (MSHA). Code of Federal Regulations (CFR), title 30, MSHA, Washington, D.C.
National Fire Protection Association (NFPA), 1 Batterymarch Park, Quincy, MA.
Occupational Safety And Health Administration (OSHA). Code of Federal Regulations (CFR), title 29, OSHA, Washington, D.C.
Office of Surface Mining Reclamation and Environment (OSMRE), Code of Federal Regulations (CFR), title 42. U.S. Department of the Interior, Washington, D.C.