Archived report · 2 min read · Set in Duncombe ·
Blasting Log at Duncombe Quarry
The quarry blasting log at Duncombe records each charge fired with an exact tonnage and time, and a single blast in the spring log is entered with no charge at all, followed by the sound of the explosion recorded by the seismograph.
- filed: Filed with the mineral extraction return
- reference: QB/DQ/03
Subject: blasting records, Duncombe quarry, north face, benches 3 to 6.
1. The quarry has been worked for limestone since 1882. Blasting takes place on weekdays between 12:00 and 13:00, under the conditions of the planning permission. Each shot is recorded in the blasting log with the date, time, charge weight, number of holes, and the recorded peak particle velocity at the nearest monitoring point.
2. Between January and April the log contains 61 entries. All of them fall within the permitted limits. The peak particle velocity ranges from 2.1 to 6.8 millimetres per second.
3. The entry for 17 April reads: charge, none. Holes, none. Time, 12:14. Peak particle velocity, 9.4 millimetres per second.
4. The monitoring seismograph at the nearest farm recorded a waveform consistent with a single blast. The record has been checked by the instrument's maintenance engineer, who confirmed the instrument was functioning correctly at the time.
5. The quarry manager confirms that no shot was fired on 17 April. The face was inspected that afternoon and showed no fresh fracture. No blast-hole drilling was carried out in the week before.
6. The blasting supervisor, who signed the entry, states that he wrote the record himself at the face at 12:14, and that he remembers the explosion. He says he remembers writing *charge, none*, because he was puzzled by it, and because a voice beside him had said that nothing needed to be broken this time.
7. Recommendation: the seismograph and the log to be reviewed by the quarry's independent consultant. The consultant reported that the waveform was not consistent with any known blasting source.
8. Observation not explained by the survey: the supervisor's signature on the entry for 17 April is dated a week later than the entry, and the handwriting of the time is the supervisor's, but the hand that wrote the word *none* is smaller, neater, and very slightly left-leaning.