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.
Blast Management
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:
- Pre-blast warnings
- Blast time
- All clear
- 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.
Misfire Procedures
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.
Blast Reports
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.
- Shot volume and powder factor calculations.
- Initiation timing schemes: in-hole delays, surface delays, and planned
hole firing times.
- 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
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.
Public Perceptions
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:
- Proper design
- Specification
- Prequalification
- Oversight
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.
Public Relations
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:
- Noise
- Vibration damage
- Danger
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:
- Managing perceptions
- 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.
Conclusion
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.
Note: Safe blasting procedures and risk management are discussed in
"Construction
Blasting Fundamentals."