Construction Blasting Risk ManagementDecember 2008As 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.by Peter G. FurstLiberty Mutual GroupTo 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 ManagementEvery 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 MeetingBefore 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:1 Acknowledge the shot is properly loaded, hooked up, secured, and ready for detonation.2 Review the blast firing time schedule.3 Review the direction of the blast movement, and define the blast area for security purposes.4 The Blaster-in-Charge should specify who should fire the shot and define the safe shot initiation location.5 Review the communication system that should be used between the Blaster-in-Charge and all blast area security personnel.6 Specify what signals should be used to announce:1 Pre-blast warnings2 Blast time3 All clear4 Blast countdown suspension7 Outline general emergency plans that should be used in case of an accident or other unplanned event.8 Review procedures for handling misfires.9 Confirm all warning signs have been postedClearing and Guarding ProceduresThe 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.1 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.2 The Blaster-in-Charge should be in constant radio communication with all personnel during the clearing and guarding operation.3 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.4 The 5-minute blast warning signal should then be sounded.5 Four minutes later, the 1-minute blast warning signal should be sounded.6 At blast time, the Blaster-in-Charge should fire or instruct the designated shot-firer to fire the blast.7 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:1 Dangerous rock conditions.2 The presence of undetonated explosives, and/or initiators.3 Abnormal blast conditions and any other hazards.8 All misfires should be safely removed, and other hazardous condition corrected or secured.9 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.10 An approved lightning detector should be used to monitor approaching electric storms. All precautions should be taken in the event of a storm.Misfire ProceduresWhen blasting misfires occuror are suspectedthe misfire procedures plan should be initiated. The Blaster-in-Charge should determine the affected area.1 No one is to enter this area for at least 30 minutes.2 Only the minimum required people should enter the area to safely re-fire, wash out, or recover unshot explosives.3 Record the location of any potentially undetonated explosives on the blast report.4 Expand the blast security area if flyrock potential is increased when misfires are re-blasted.Blast Emergency PlanThe elements of specific blast emergency plans should vary based on the unique site conditions. The plan as a minimum should include the following.1 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.2 Plan should be clearly communicated and understood by all personnel.3 Define notification procedures and their timing.4 Identify location of first-aid kits and identify first-aid providers.Blast ReportsIndividual blast reports should be prepared for each blast. Blast reports should include the following.1 Blast date, time, and location2 Weather end environmental conditions, such as wind speed and direction.3 Blast geometry: hole size(s), hole depth, drill pattern, number of holes, bench height, and sub-drilling.4 Blast hole loading summaries: typical hole loads, explosive types, primers, detonator delays, stemming type and quantity, as well as total explosive utilized, byproduct.5 Shot volume and powder factor calculations.6 Initiation timing schemes: in-hole delays, surface delays, and planned hole firing times.7 Blast effect monitoring data (such as ground vibration levels, air-over-pressure measurements).8 Notes about blasting results.9 Name and signature of blaster-in-charge.Risk ManagementRisk 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 PerceptionsThe 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 amongst 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 RiskEngineers 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:1 Proper design2 Specification3 Prequalification4 OversightUnless 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 RelationsAll blasting projectslarge or smalloccurring 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 ConcernGenerally the neighbors' areas of concern fall into three categories: Noise Vibration damage DangerPlanned PR StepsIt 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 messagePre-Blast and After-Claim Property Condition SurveyPre-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.ConclusionIt 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."

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1. Contrato entre GM o propietario de terrenos y Marco A. Jimnez2. Ttulos de propiedad de los terrenos (copia certificada)3. Copia de Poder Notarial de representante legal4. Copia Notarial Identificacin oficial de representante legal5. Copia Notarial Comprobante de domicilio de representante legal6. Estado civil de represntate legal

Renta mensual de maquinaria1. Renta de dos excavadoras CAT 330 o similar2. Renta de bulldozer D8 o similar

Plan de trabajo para excavacinExcavaciones en roca Planeacion GeneralEl plan general de excavacin se formula tomando en cuenta los factores externos, entre los que destacan el tiempo total de excavacin as como los recursos existentes.

La planeacin de cada fase se realiza en base a los tiempos dados en la planeacin general y en el proceso de cuantificacin del tiempo. Cuando stos relacionados con las unidades de cuantificacin (m3 slidos, tronadas, metros de barrenacin, alturas de bancos, y cantidades de explosivos, etc.) La necesidad de capacidad de cada fase est determinada. Esta ser la base para escoger el mtodo de explotacin y el equipo.BarrenacinEsta actividad consiste en efectuar perforaciones necesarias en el frente de trabajo.

Para realizar esta se debe tomar en cuenta:

Alturas de bancos econmicas.Metros de barrenacin por m3 de slidos (m/barreno/ton) endiferentes secciones transversales.Espaciamiento ptimo de los barrenos en el banco y en el perfil.Dimetro econmico de los barrenos.

El tipo ms simple de modelo de perforacin es una lnea recta de barrenos verticales paralelos a un frente vertical. La distancia de cada barreno al frente se llama bordo ; y la distancia entre barrenos , su espaciamiento.Carga de Explosivos y voladuraEl plan de carga de explosivos siempre est basado en el plan de barrenacin, el cual determina por ejemplo la cantidad de explosivos por usar. Los siguientes factores deben ser considerados cuando se prepara el plan de carga de explosivos.

Eleccin econmica de explosivos.Determinacin de la capacidad de explosivos necesarios.Eleccin del sistema de iniciacin y tipo de detonador.Proteccin y seguridad: ejemplos: riesgo de daos, probabilidad de accidentes, dispersin de los fragmentos de roca, vibraciones del suelo, etc.El encargado de Obra o Proceso debe ejecutar el trabajo de voladura de acuerdo con las normativas de manejo y uso de explosivos existentes de manera que el riesgo de accidente sea minimo. Las plantillas de voladura deben ser disenadas de manera que se respeten las lineas teoricas de excavacion planteadas en planos. Toda excavacion en roca se hara siguiendo los procedimientos mas seguros y eficientes. Se debe procurar el minimo de personal necesario, estableciendo claramente los limites de la excavacion y el alcance de las explosiones, ademas se deben identificar los posibles efectos en areas vecinas. Cualquiera de las tecnicas utilizadas por el Encargado de Obra o Proceso (recorte, pre-corte o voladura amortiguada), debe garantizar la minima sobre excavacion posible, el Ingeniero de obra determina el medio de control que le permita realizar los ajustes necesarios. Ademas las vibraciones producidas por la detonacion deberan estar dentro de los niveles maximos permitidos y al igual que en el caso de la sobre excavacion contar con los mecanismos de control adecuados que brinden los datos de la manera mas clara y rapida posible. Las excavaciones en roca que se desarrollen deberan considerar la presencia de otras obras y estructuras a su alrededor con el fin de establecer las velocidades minimas aceptables que garanticen la estabilidad y seguridad de cada elemento. Si no existe una investigacion preliminar a menos deben de considerarse los siguientes parametros: Velocidades de Excavacion Para masas de Roca (Criterio Bauer y Calder)

Sin fracturacion de roca intacta Velocidades menores a 254 mm/s

Permitido el lajamiento menor de la masa de roca Velocidades entre 254 a 635 mm/s

Tuneles (Langefors)

Para evitar desprendimiento de roca en procesos de excavacion Velocidades menores a los 300 mm/s

Estos factores podrian variar de acuerdo a las calidades de la roca y de los equipos que se tengan en los procesos de excavacion, otros criterios sugieren velocidades no mayores a 100 mm/s.

Estructuras Construidas (Criterio Canmet, Bauer y Calder)

Interruptores de mercurio en montura rigida Menor a 13 mm/s

Casas y oficinas Menor a 50 mm/s (puede ser menor dependiendo del tipo de construccion y calidad de la misma.

Perforaciones encamisadas Menor a 380 mm/s

Equipo mecanico, bombas, compresores Menor a 1000 mm/s

Concreto Endurecido

Colado de 1 dia 14 mm/s

Colado de 2 dias 30 mm/s

Colado de 3 dias 40 mm/s

Colado de 7 dias 60 mm/s

Colado de 28 dias 85 mm/s

Colado de 90 dias 100 mm/s

En todo caso si se tiene duda al respecto debera darse al menos 72 horas de tiempo.

Previo a cualquier actividad debe levantarse un registro fotografico que permita evaluar las posibles evidencias de cambio de las masas de roca, taludes o estructuras; este levantamiento fotografico debe ademas tener una elevacion tecnica del grupo ejecutor si asi se considera en aquellos elementos considerados criticos. La tecnica a usar debe ser disenada y aprobada por un especialista en explosivos, previamente definido por la Direccion y la Jefatura Constructiva, considerando lo siguiente: Cuando hay excavaciones en roca contra la cual se construiran estructuras, o excavaciones que esten cerca de otras estructuras, se deben hacer voladuras cuidadosamente controladas; en cuyo caso la velocidad de vibracion maxima permisible en obras o terrenos es la siguiente: Estructuras de hormigon: 100 mm/seg. Roca no revestida. : 70mm/se Con el fin de reducir a un minimo la sobre excavacion en el piso de una excavacion, la ultima bancada de roca sobre la cota de fundacion debera tener como maximo 4m de altura y debe ademas ser excavada empleando perforaciones en numero, diametro e inclinacion, acordes con un desarrollo controlado en cada explosion. El uso de explosivos de baja potencia y velocidad de detonacion es recomendable, de modo de limitar o minimizar la sobre excavacion teorica. Se deben tomar precauciones especiales con las voladuras que queden proximas a los paramentos laterales de una excavacion, los que deben sufrir el menor dano posible. En general estas precauciones se tomaran en una franja de 4 m minimo de ancho, paralela al paramento, salvo indicacion distinta en los planos o en las especificaciones tecnicas particulares a la obra en construccion. En caso de ser necesarios disparos cerca de estructuras recien hormigonadas, las velocidades permitidas deben ser menores para no correr el riesgo de dano. Los valores deben ser definidos en funcion de la edad de curado de la estructura, siendo la velocidad maxima permitida aquella permitida a los 28 dias de curado. Las voladuras no satisfactorias, por causa de excesiva sobre-excavacion o danos a estructuras o instalaciones vecinas, seran suspendidas, y se exigira al Encargado de Obra o Proceso demostrar, mediante un analisis o la opinion de un experto, el uso satisfactorio de otro sistema que garantice el adecuado desarrollo de la obra. El Encargado de Obra o Proceso debera constantemente vigilar la estabilidad de los cortes y taludes, haciendo los trabajos necesarios para evitar que elementos externos puedan desestabilizar la obra. En general, debera asesorarse con la opinion de un especialista en el tema. Carga, transporte y descarga del material producto de la excavacinSe considerara para estas actividades:

Seleccionar el tipo de cargadorEspacios para maniobrasSuperficie y calidadCantidad de material producto de la voladura

Los cargadores son equipos de excavacin, carga y acarreo y por esta causa es ms conveniente en algunos casos que la pala mecnica, pues en sta es necesario el uso de camiones para el acarreo del material aunque sea a distancias cortas.