Safety first, blast next

The use of explosives in construction work is both an art as well as a science. It is a practical art which takes many years of experience to wholly appreciate the finer points of handling and usage.

As a science, it requires considerable engineering knowledge of explosives and their effect on a variety of materials.

There is often a need to use explosives for site development (to remove rock depositions before starting actual construction activities).

If one does not handle explosives with utmost care, it may lead to serious work-related injuries and at times can lead to fatalities also.

The laws of our country that deal with the usage of explosives are very stringent. With construction going on in urban areas, we have very little margin for error.

While working with explosives we need to give attention to the following:

Obtain valid licenses for possession, storage, transportation and usage of explosives;

Licensed vehicle for transportation of explosives;

Never store detonators and explosives in the same container;

Only an authorised person should be allowed to handle explosives.
Timing

People often conduct blasting operations at their convenience and cause discomfort to the local residents.

Generally blasting operations need to be conducted during noon, during lunch or in the evening before sunset. But we even observe blasting operations being conducted in the early hours of the day.

While conducting blasting operations, one need to ascertain that throw of rock (fragments) is controlled. We call this controlled blasting.

This is done by using engineering controls viz. delay detonators / relay cords and by covering the blast area with proper tyre mats etc.

Also it is advised that one needs to inform the local residents about the timing of blasting operations.

Often people don’t use detonating fuses as it increases the cost of operation marginally. By adopting this method, management of misfires becomes relatively easy.

Also we need to ensure that blasting induced earth vibrations are not transmitted to the adjoining habitation by creating a cut off zone / free face.
Precautions

1. Do not use defective explosives, explosives known/ suspected to be defective.

2. Public Relations: to avoid complaints it is essential that all persons within a reasonable distance are advised beforehand of what is going to take place, when it’s going to take place, and what signals will be used prior to each blast and the safety precautions to be taken when this is happening.

3. System and control of debris: plan ahead for a systematic work pattern so that holes can be set to a definite pattern, marked, and drilled to fixed lines. Accurate tamping with an adequate quantity of good stemming material can minimise some of the fly rock.

4. Log Book: it is advisable to keep a log book which should be of a stout note or exercise book type. In it record the date, time, location, layout or pattern depths, size of charges, detonators used, type of material, weather and direction of wind, cover used and the results obtained.

5. Prevention of fly rock or debris: it is the responsibility of the construction blaster to ensure that no undue scatter or damage to property occurs when blasting is carried out.

6. Size of danger area: it has to be cleared of personnel before a blast will depend on such things as:

(a) The size of the blast;

(b) The type of blast;

(c) The covering of the blast area;

(d) The direction and strength of any wind;

(e) The nature of the material to be blasted, such as steel or cast iron, which may fly a long distance.

7. Vibration damage area: there is a long history of damage attributed to, rightly or wrongly, explosive generated vibrations.

Usually complaints are received concerning damage to brick work, fibrous plaster, glass, and roofing tiles and are often magnified.

Seismologists have proved that structural damage is due to particle velocity rather than particle displacement or acceleration.

Therefore it is the speed with which the ground under the structure is moved by the passing seismic or ground waves that determines the possibility of damage.

8. Warning signals: a system of warning signals should be used on construction work.

Danger notices with the blasting signal code should be erected on all roads and tracks leading to the blasting area site.

9. Sentries: before a blast is fired, guards or sentries with red flags should be posted at strategic points and entries to the area, to prohibit any person from entering the danger area until after the blast is fired and an all-clear is given.

10. Misfires: with few exceptions, misfires are traceable to poor workmanship, ineptitude on the part of those preparing loading and firing of explosive charges, or failure to adhere strictly to standards of good practice.

11. Pre-drilling precautions: no hole shall be drilled in any face till the face within the radius of 1 m from the intended hole has been cleaned and washed down and any cut-offs or butts have been thoroughly washed down and examined by two persons, and found not to contain explosives.

12. Shattered ground: if the ground around the misfire has been shattered, the relieving hole method should not be used.

In this case the ground around the misfire must be carefully cleared till the explosives are uncovered.

This must be done cautiously by following the wires or fuses down to the charge, removing the last few inches of cover by hand.

13. Misfire personnel: the construction blaster must investigate and carry out the misfire treatment.

It is only when we stringently follow all the processes will we able to guarantee complete construction site safety during blasting.

ASWATHA NARAYANA
SENIOR MANAGER-HSE

MAYTAS INFRA LTD