As we can see from the November 2008 article, "Construction Blasting Fundamentals," there are many forms of risk associated with blasting work. It is clear that, despite these risks, experience reveals that blasting can be performed without incident, when adequate risk-control measures are used to manage the work.
To ensure safe blasting procedures, it is very critical to understand the terminology used in the specifications. As a general rule of thumb:
The "blast site" is the area where explosive material is handled during loading, including an area extending at least 50 feet in all directions. The "blast area" is the entire zone that may be affected in any way by the blast.
Every blasting operation must have a "Blaster-in-Charge" (BIC). This individual has overall responsibility for all aspects of the blasting operations. Prior to any blasting, the general and site-specific blasting hazards and environmental impacts must be defined for each blast site. Blasting plans and procedures must incorporate all reasonable measures necessary to eliminate negative impacts on persons, property, and the environment.
Explosive storage on-site should be limited as much as possible, but if this is necessary, then all federal, state, and local regulations governing explosive storage must be followed.
In blasting design there are generally two major considerations: safety concerns and operational concerns. Safety concerns should always come first.
Pre-Blast Review Meeting
Before blasting, the Blaster-in-Charge should assemble all blast crew personnel to review the blast area security plan and blast emergency plan. The blast area is the area in which there is any potential for flying material, air over-pressure, or gases from an explosion to cause injury to persons. The Blaster-in-Charge should cover the following issues:
Acknowledge the shot is properly loaded, hooked up, secured, and ready for detonation.
Review the blast firing time schedule.
Review the direction of the blast movement, and define the blast area for security purposes.
The Blaster-in-Charge should specify who should fire the shot and define the safe shot initiation location.
Review the communication system that should be used between the Blaster-in-Charge and all blast area security personnel.
Specify what signals should be used to announce:
Blast countdown suspension
Outline general emergency plans that should be used in case of an accident or other unplanned event
Review procedures for handling misfires.
Confirm all warning signs have been posted
Clearing and Guarding Procedures
The Blaster-in-Charge should coordinate blasts, with all concerned parties, on an approved schedule. To do so, clearing and guarding procedures must be set, communicated, maintained, and evaluated.
A safe area around the shot area should be determined and cleared. Guards should be assigned to secure all possible entryways into the blast area.
The Blaster-in-Charge should be in constant radio communication with all personnel during the clearing and guarding operation.
When all guards confirm that the area is secure, the Blaster-in-Charge should connect the primary initiation device 5 minutes before the scheduled blast time.
The 5-minute blast warning signal should then be sounded.
Four minutes later, the 1-minute blast warning signal should be sounded.
At blast time, the Blaster-in-Charge should fire or instruct the designated shot-firer to fire the blast.
After the post-blast fumes have dissipated to safe levels, the Blaster-in-Charge should inspect the shot area. During the examination the blaster should look for:
Dangerous rock conditions.
The presence of undetonated explosives, and/or initiators.
Abnormal blast conditions and any other hazards.
All misfires should be safely removed, and other hazardous condition corrected or secured.
When the area is clear of hazards to nearby traffic, the public, or the job site personnel, the Blaster-in-Charge should give the all-clear signal and relieve the guards from their posts.
An approved lightning detector should be used to monitor approaching electric storms. All precautions should be taken in the event of a storm.
When blasting misfires occur—or are suspected—the misfire procedures plan should be initiated. The Blaster-in-Charge should determine the affected area.
No one is to enter this area for at least 30 minutes.
Only the minimum required people should enter the area to safely re-fire, wash out, or recover unshot explosives.
Record the location of any potentially undetonated explosives on the blast report.
Expand the blast security area if flyrock potential is increased when misfires are re-blasted.
Blast Emergency Plan
The elements of specific blast emergency plans should vary based on the unique site conditions. The plan as a minimum should include the following.
Post all emergency response telephone numbers, including medical response, OSHA, MSHA, fire department, police, state regulatory authorities, home phone numbers of all site supervisors and workers.
Plan should be clearly communicated and understood by all personnel.
Define notification procedures and their timing.
Identify location of first-aid kits and identify first-aid providers.
Individual blast reports should be prepared for each blast. Blast reports should include the following.
Blast date, time, and location
Weather end environmental conditions, such as wind speed and direction.
Blast geometry: hole size(s), hole depth, drill pattern, number of holes, bench height, and sub-drilling.
Blast hole loading summaries: typical hole loads, explosive types, primers, detonator delays, stemming type and quantity, as well as total explosive utilized, byproduct.
Blast effect monitoring data (such as ground vibration levels, air-over-pressure measurements).
Notes about blasting results.
Name and signature of blaster-in-charge.
Risk management in blasting work is increasingly becoming more challenging as work inevitably occurs in more populated areas. Not only is the work closer to people and structures, but concern about blasting effects on animals and utilities are also increasing. Sometimes it is possible to use mechanical methods to excavate rock, but these are slower, costly, and may still have vibration issues. Regardless of the scale of the blasting work, sometimes engineers and contractors underestimate the importance of preparing blasting controls and public relations programs. The consequences of this are often severe.
The public's perception of blasting has been forged from scenes in movies like Die Hard and Apocalypse Now. People do not want blasting occurring, or explosives stored, near their homes. Some recent tragedies with explosives have created genuine fear among the general public. In light of these liabilities and public relation issues, it is imperative to ensure that the blasting plan is as foolproof as possible, and the public informed about the work planned for the site and educated about blasting, its effects, and the controls put in place for everyone's protection.
For most projects, engineers develop blasting specifications designed to ensure that blasting is done safely and in conformance with project requirements. The quality and thoroughness of the specifications can greatly affect the outcome of the project. In most cases, risk is transferred by contract clauses, but in some serious cases, owners and others have become embroiled in legal action and have ended up with financial losses.
Contractors and blasters usually understand the risk associated with the work. Occasional accidents and incidents, such as flyrock and premature detonation, are the result when blasters do not employ adequate blast design and control practices. Along with these well-known risks, there are secondary risks such as vibration and air overpressure that result from blasting operations. Other issues that may have some impact may involve explosives storage and transportation.
Managing Blasting Risk
Engineers and planners can use the following approach to manage blasting risk. First, ensure that the project design is practical. Second, define prequalification requirements for the contractors who are to bid on the project. Third, develop specifications that clearly define performance and safety requirements for the work. Fourth, ensure that the work is overseen by capable personnel.
Safe blasting requires four basic elements:
Unless property is damaged by flyrock, most claims of damage caused by vibration and air overpressure are "perceived" damage claims, where observed damage may have been caused by other conditions such as settlement, poor construction, weathering, differential temperature, and humidity.
All blasting projects—large or small—occurring near any concerned neighbors, require some level of public relations work. The level of this public relations (PR) work is a function of the blasting duration, timing, and the level of concern by the neighbors. Engineers and designers understand that it is unlikely that the planned blasting will cause any real injuries to the neighbors or damage their property. Because of this belief, it is sometime hard for them to become enthused about PR work. The neighbors, however, have a different impression of explosives, which is gained from popular TV, movies, and well-publicized accidents or disasters. So, ignoring the public is to invite potential delays and eventually costly legal action.
Issues of Concern
Generally the neighbors' areas of concern fall into three categories:
Planned PR Steps
It is usually a good idea to hire a competent public relations firm to handle the PR issues as they relate to the project. The activities include:
Dealing with issues and concerns
Listening and communicating about the risk
Delivering a consistent message
Pre-Blast and After-Claim Property Condition Survey
Pre-blast surveys are an extremely important tool for prevention of blasting complaints and subsequent damage claims. In many cases, pre-blast surveys lower the project liability risk, as well as serve as a venue to educate the neighboring public. A professionally performed survey also will influence the attitude of the adjoining property owners. Depending on the project, the area surveyed can be as close as 300 feet or half a mile and greater.
Pre-blast reports should include written notes, photographs, or video, and in some cases, diagrams and measurements to classify existing conditions. Settlement surveys by independent firms may also be necessary. The surveyors should be given some PR training so that they may effectively start the public education process.
It is important to understand that risk management starts well before the blaster shows up for work on the project. Engineers and planners must ensure that the project design is practical. The contractors are prequalified to ensure that they are capable to successfully perform the work. The specifications must clearly define the performance and safety requirements of the work. And that the work is overseen by qualified and capable construction personnel at all levels.
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