Blasting in quarries and works: the 72-hour notice, the seismographs and the inspection of your home

It is Rule 3.5.13 of Chapter 3.5 of Joint Regulation No. 9473, on the use of explosives as a method for breaking rock in extraction and excavation activities. It covers when it applies, the handling and notification standards, the critical detonation design, the test and production detonations with their vibration and airblast limits, the pre- and post-blast inspections of neighbouring homes, and the use and installation of seismographs. It is not the criminal explosives act: the penalties for illegal use and possession are in Act 134-1969 as amended by Act 88-2026, and they have their own guide on this site. This is the regulatory, operational part, and the one that gives concrete tools to a quarry’s neighbour.

The rule applies to every extraction and excavation activity involving the earth’s crust components that requires the use of explosives as a method for breaking rock, provided it is associated with the processing of original, renewal or amendment applications for three permits: the Formal Permit, the Incidental to an Authorised Work Permit and the Incidental Activity to an Infrastructure Work Permit. The use of explosives does not apply to the processing of any other permit type in the chapter, except where it is necessary to address an emergency, urgency or public-interest situation, where a qualified professional is consulted. And if, after an activity is authorised without explosives, the need arises to use them to break an unexpected rock outcrop, a qualified professional is consulted and the corresponding amendment to the originally authorised permit is requested.

• That the handling and use of explosives be carried out solely and exclusively by persons duly authorised by the Puerto Rico Police Bureau, whose licences and permits are not expired, suspended or cancelled, and that every detonation be directly supervised by certified and licensed personnel.Verified against the official source
• Notifying the Puerto Rico Police Bureau at the nearest station and the DRNA’s Cuerpo de Vigilantes at the nearest Regional Office seventy-two hours before the use of explosives, and keeping a logbook with the date, time and names of those notified.Verified against the official source
• Keeping, duly safeguarded for five years and preferably at the operations site, a chronological record of every test and production detonation and of every seismographic reading, available for inspection by prior coordination by DRNA and Planning Board officials.Verified against the official source
• Signposting the permit area warning of the use of explosives, with signs of resistant materials and techniques, of a minimum size of two feet by three feet, placed at every vehicular access from a main public road.Verified against the official source
• Carrying out the test detonations during the permit’s first sixty calendar days, hiring an independent licensed engineer to supervise them and certify in writing their compliance with the design submitted.Verified against the official source
• Having at least three seismographs available during the test, duly calibrated with calibration certificates not older than one year.Verified against the official source
• That the airblast resulting from a production detonation not exceed 4.2 pounds per square foot, measured by air-pressure instruments located where the seismographs are required.Verified against the official source
• That in granular soils susceptible to vibration densification — clean, loose, ungraded sands — the shear strain generated by the vibration not exceed 0.005%.Verified against the official source

• The critical detonation design, complemented by plan and section drawings with the quarry’s or project’s name and location, the designer’s name and explosives licence number, the type of material, the bores’ location and pattern, the detonators and their delay sequence, the type and quantity of explosive total and per delay, the stemming depth, the distance to the centroid and the expected particle velocity.
• The chronological record of every detonation, with the quarry’s or project’s name, the location, the date and time, the blaster’s information and licence number, the sketch of the bores, the detonators and explosives by weight, the stemming depth, the seismographic reading number, notes on any deviation from the parameters, the distance from the centroid to the nearest structure outside the finca, the use or omission of flyrock provisions and the occurrence of flyrock beyond the limits.
• The independent licensed engineer’s technical report certifying the test detonations’ compliance with the design submitted, with a comparative analysis between what was predicted and what occurred and copies of the vibration records.
• The pre- and post-blast inspection report, with the graphic inventory to scale of all the structure’s deficiencies — floor, walls, columns, beams, ceiling, the roof’s exterior surface, finishes, pathways, pavements and fences — sample photographs, and the date, time, address and signature of the owner, tenant, occupant or delegated person.
• The quarterly report the independent licensed engineer submits to OGPe summarising the production-detonation results generated by the seismographs and stating compliance with the section.

1. 1

   Step 1: Who may blast and who must be told

   The handling and use of explosives is carried out solely and exclusively by persons duly authorised by the Puerto Rico Police Bureau whose licences and permits are not expired, suspended or cancelled; every detonation must be directly supervised by duly certified and licensed personnel. And the Police Bureau at the nearest station and the DRNA’s Cuerpo de Vigilantes at the nearest Regional Office must be notified seventy-two hours before the use of explosives, keeping a logbook with the date, time and names of those notified. That seventy-two-hour notice is verifiable: the logbook exists and officials may ask for it.

2. 2

   Step 2: When this rule applies and when the permit must be amended

   Every extraction and excavation activity requiring the use of explosives as a method for breaking rock must comply with this rule, provided it is associated with the processing of original, renewal or amendment applications for the Formal Permit, the Incidental to an Authorised Work Permit or the Incidental Activity to an Infrastructure Work Permit. Once the requirements are determined, the operational conditions are included in the corresponding permit. And if, after an activity is authorised without explosives, the need arises to use them to break an unexpected rock outcrop, a qualified professional is consulted on the detonation’s design and supervision, safety and public welfare are considered, and the corresponding amendment to the originally authorised permit is requested. A note of fidelity: the regulation sends the emergency, urgency or public-interest case to the considerations of "Rule 3.5.12", but that rule is the Export Permit and contains no such considerations. We report the cross-reference as it stands and do not correct it.

3. 3

   Step 3: The operating standards: the more restrictive prevails

   Compliance is required with Act No. 134 of 28 June 1969, the Puerto Rico Explosives Act, and its Regulation of 11 September 1970, and with the applicable OSHA or MSHA requirements. And the regulation settles the clash of standards clearly: where there is conflict or discrepancy between the federal regulations and the one contained in the Joint Regulation, the more restrictive prevails. Quarry and construction operations requiring explosives must use the cut-and-terrace method where applicable, and the slope inclination, the resulting free faces and the terrace spacing are determined by a licensed geotechnical or geology professional according to the site’s geological conditions.

4. 4

   Step 4: Flyrock, noise and the two-by-three-foot sign

   Explosive operations are carried out taking due precautions to minimise vibration, noise and flyrock as far as possible, especially under confinement, so as not to affect constructions, properties, roads or public works adjacent to the finca’s or project’s perimeter. Where there is determined to be a high probability of flyrock leaving the area, steel mesh, overburden or another acceptable alternative method must be used as a minimum safety measure. The permit area must be signposted warning of the use of explosives, with signs of resistant materials and techniques, of a minimum size of two by three feet, placed at every vehicular access from a main public road, with the quarry’s or project’s name and the extraction permit number. And on noise, the regulation suggests that at least eighty per cent of detonations keep the noise below one hundred and twenty decibels, measured at the structure nearest the detonation located outside the finca’s or project’s area.

5. 5

   Step 5: The critical detonation: what it is and how it is predicted

   The critical detonation is the production detonation anticipated to induce in the nearest structures, outside the finca’s or project’s area, the greatest-magnitude vibration, expressed as particle velocity. The prediction rests on a mathematical expression recognised in the best practice of geophysics, structural engineering or explosives handling; in the absence of a more specific one, the regulation provides the particle-velocity equation V=Ks(D/W to the one-half) to the power n, where V is the particle velocity, Ks the soil’s transmissibility factor, D the distance from the detonation’s centroid to the critical structure in feet, W the maximum quantity of explosive per delay — with an interval not less than eight milliseconds — in pounds, and n the attenuation factor. The design comes with plan and section drawings carrying the designer’s name and explosives handling licence number.

6. 6

   Step 6: Before the test: the limits on preparatory blasts

   The detonations necessary for site preparation, creating terraces and accesses, boulder breaking or rock pre-splitting, among others, prior to the test detonation, are designed so the particle velocity at the nearest structure outside the finca’s or project’s area does not exceed 0.10 inches per second for quarries and operations with the usual quarry characteristics, and 0.20 on construction projects. Those designs need not be submitted to OGPe, but a pre-consulta must be filed with OGPe for authorisation.

7. 7

   Step 7: The permit is issued without production authorisation

   This is the point that surprises most. Once all the technical-legal evaluations conclude favourably and the permit’s viability is determined, it is issued without including authorisation to carry out production detonations: the permit only includes the details of site preparation and the test detonations. Those tests must be carried out during the permit’s first sixty calendar days. If they prove satisfactory, production detonations are authorised by amendment to the original permit. That is: holding the permit does not yet authorise producing with explosives.

8. 8

   Step 8: The test: three seismographs and three stages

   The applicant presents at least three alternate dates for the test detonation, and must hire the professional services of an independent licensed engineer to supervise it and certify in writing that it complied with the design and with the rule. They must have at least three seismographs available during the test: the first, S1, beside the structure nearest the detonation area; the other two, S2 and S3, along an imaginary line through S1 and the detonation’s centroid, with S3 at the farthest place and S2 halfway. The test is executed in three stages: the first with thirty-three per cent of the design charge, the second with sixty-six per cent and the third with one hundred per cent; each stage is implemented only if the preceding stage’s seismographic readings did not exceed what was anticipated or what the rule requires. And where access to private property is not permitted for siting the seismographs, the best alternative location is chosen and the reasons documented.

9. 9

   Step 9: Production detonations and what is measured

   Production detonations are carried out as described in the permit, and any request to amend the critical design must be justified in writing, which may include using a site-specific scaled-distance value based on the records of not less than twenty-five production detonations. Two things are measured. The airblast, measured by air-pressure instruments, may not exceed 4.2 pounds per square foot, using a 2 Hz high-pass measurement system, with the instruments located where the seismographs go. And the seismic wave, measured in particle velocity in inches per second and dominant frequency in Hertz, for each of the three orthogonal components of vibration: none of the three velocity-frequency pairs may exceed the applicable curves of the spectral graph, and the resultant vector of the three combined is not considered in the evaluation. In the official copy we read, that graph — Figure 2 — is only partly legible, so we publish no figure taken from its curves here.

10. 10

    Step 10: What the three curves of Figure 2 represent

    Although we cannot read the values, the regulation does explain in words what each curve is, and that we do reproduce. Curve 1 is an empirical curve of permissible values reflecting observations of surface — aesthetic — cracking, to which a safety factor has been applied; it does not contemplate architectural or structural impairment effects, which correspond to greater magnitudes. Curve 2 is an empirical curve of permissible values regarding human response to transient non-periodic vibration, to minimise annoyance to neighbours caused by detonations on construction projects, provided blasting at the maximum permitted at the same place does not run more than two consecutive weeks; otherwise Curve 3 is used. And Curve 3 is the equivalent for detonations with the usual quarry characteristics. On construction projects a waiver may be requested to exceed Curve 2 provided Curve 1 is not exceeded, accompanied by a Memorial Explicativo. Here the document contradicts itself: one paragraph says that waiver is requested from the DRNA and the next, almost identical, says it is requested from OGPe. We reproduce both versions and choose between neither: you must ask OGPe.

11. 11

    Step 11: If you are a neighbour: the inspection of your home before they blast

    Pre-blast inspections are carried out only before the test detonations, and their purpose is to prepare an inventory of the existing aesthetic, architectural and structural deficiencies in the structures inspected. They apply where a new quarry is established and explosives are sought, where a quarry that has not used explosives applies to use them, where the expected particle velocity is greater than 0.25 inches per second — except in quarries already operating with explosives at the Regulation’s start — and where the DRNA and the Planning Board deem it necessary. The three neighbouring structures nearest the seismograph locations are inspected, coordinated and supervised by an independent licensed engineer who submits a certified report, and additionally at least twenty-five per cent of all structures within the zone defined by the value of D, distributed in three subzones of equal width: sixty-five per cent in the nearest, twenty-five per cent in the intermediate and ten per cent in the farthest.

12. 12

    Step 12: What the inspection report carries, and what happens if you refuse entry

    The report includes an inventory of all the structure’s deficiencies — the floor, walls, columns, beams, ceiling, the roof’s exterior surface, the finishes with special emphasis on floor tiles, wall tiles, renders, stucco, mirrors, glass and door and window frames, the pathways and pavements, and the fences — in graphic format and showing to scale the deficiencies’ lengths and configurations. In the nearest, farthest and intermediate structures, the maximum width and length of several representative wall and ceiling cracks are measured and noted. Sample photographs of the most significant and most usual deficiencies are attached, and the report states the date and time, the structure’s address and the name and signature of the owner, tenant, occupant or delegated person. Inspections are carried out in that person’s presence; if access is refused, it is documented in an acta with the date and time of the attempt, the person’s name and title, the address, the reason for the refusal, the inspector’s name and the signatures, with a photograph of the main façade attached, and an alternate structure is then selected to meet the required percentage.

13. 13

    Step 13: If you file a complaint about the detonations

    Where there is a complaint about a detonation, a second seismograph is installed beside the complainant’s structure for at least one production shot. In a building of two or more storeys, the seismograph’s sensor is placed on the floor of the complainant’s level. These readings are not required if the structure is located farther than the calculated value of D. One complainant is attended at a time, and if after three readings the vibration limits set in the permit are shown not to have been exceeded, readings for that structure stop. Moreover, post-blast inspections may be required of structures previously pre-inspected to address complaint claims, and if the complaint concerns a structure never inspected, a neighbouring structure that was inspected is used as the comparative reference.

14. 14

    Step 14: The seismographs: calibration, placement and the quarterly report

    Seismographs must be duly calibrated with calibration certificates not older than one year. An independent licensed engineer coordinates and supervises the installation and operation of those used during the test detonation, examines the production-detonation results and submits a quarterly report to OGPe summarising them and stating compliance. The sensor is installed on firm ground, never on the vegetal layer nor on grass or other vegetation, and on pavement only where that is the only option, in which case it is coupled by bolt anchoring. It is placed not more than ten feet from the structure, or not more than ten per cent of the distance to the detonation’s centroid, whichever is less. The coupling changes with the expected acceleration: below 1.0 g, a spike buried in firm ground or a loose sandbag of at least half a cubic foot over the sensor; above 1.0 g, the sensor is buried and spike-coupled, with the excavation’s bottom not less than three times the sensor’s thickness and the backfill hand-compacted.

The use of explosives is authorised inside the extraction permit, before OGPe and through the SUI: the critical detonation design is filed with the application, and production detonations are authorised afterwards by amendment to the permit. The pre-consulta for preparatory blasts also goes to OGPe, and the independent licensed engineer’s quarterly report is submitted there. The seventy-two-hour notice before each use of explosives goes to the nearest station of the Puerto Rico Police Bureau and the nearest Regional Office of the DRNA’s Cuerpo de Vigilantes. The records are kept at the operations site and inspected, by prior coordination, by DRNA and Planning Board officials.

• Blasting without notifying the nearest Police station and the DRNA’s Cuerpo de Vigilantes seventy-two hours in advance.
• Not keeping the logbook with the date, time and names of those notified.
• Assuming the permit already authorises production detonations: it is issued only with site preparation and tests.
• Letting the first sixty calendar days of validity pass without carrying out the test detonations.
• Running the test with fewer than three seismographs, or with instruments whose calibration certificate is older than a year.
• Skipping the thirty-three and sixty-six per cent stages and blasting straight to one hundred per cent of the design charge.
• Installing the seismograph’s sensor on the vegetal layer, grass or other vegetation.
• Placing the sensor more than ten feet from the structure when that is the smaller applicable limit.
• Operating without the two-by-three-foot signs at every vehicular access from a main public road.
• As a neighbour, refusing access to the pre-blast inspection and being left without a baseline inventory of your home.

These are the government pages this guide is based on.

• Oficina de Gerencia de Permisos (OGPe)

  OGPe

  docs.pr.gov

• Permit Management Office

  ogpe

  ogpe.pr.gov

• Department of Natural and Environmental Resources

  drna

  www.drna.pr.gov