Non-Detonating 1.4S Cartridges
What are they?
Class 1.4S rock breaking cartridges are an effective tool for breaking rocks. They are considered a low explosive for regulatory purposes, and can be shipped Fedex, UPS or in a private vehicle in most cases.
How do they work?
They work in a somewhat different way than high explosives do. Rather than detonating instantaneously to shatter rock by compression, they generate gas pressure that breaks it in tension.
As pressure rises inside the borehole. the reaction speed increases and more pressure is generated. When the rock starts to fail, it cracks and releases the pressure. Any remaining propellant burns off at this point and the reaction stops.
Are there advantages over high explosives?
The typical vibration and flyrock problems associated with high explosives such as dynamite and ANFO can be greatly reduced when these products are used correctly. Evacuation distance is typically around 50m on smaller shots and vibration level is around 1/2 of a comparable shot with HE products.
ACCX Research is an ATF-licensed importer of explosives and can supply a wide variety of 1.4S products.
Blasting with 1.4S Overview
First, holes are layed out and drilled into the rock in the same manner as it is done for high explosives. The cartridges are then loaded. As with all explosives, a wooden loading pole is used and standard safety precautions are taken.
When breaking boulders, very low powder factors can be used, typically 40g per cubic yard or less. Typical burden for the smaller cartridges is 2-3′ from holes to a free face.
Stemming is key
Once the holes have been loaded, they are stemmed with small, sharp gravel. Good stemming is crucial to the performance of these cartridges, as they material will simply burn in the absence of confinement.
The cartridges also work best when the rock is relatively free of defects and existing fractures. A good test is to pour 1-2 liters of water into a freshly-drilled hole. If it holds the water or only drains slowly, it’s likely to be a good candidate for 1.4 blasting.
Where the rock is fragmented or rotten, expanding grout may be a better choice.
Initiation
These cartridges are electrically primed with either a built-in igniter or a special delay igniter that looks like a blasting cap. Standard detonators can also be used with some products, such as the Royex Gen 2.
It is a good practice to test the firing circuits and make sure that any igniters to be wired in series read within 0.5 ohms of each other, especially if mixing products or lots.
Fragmentation and Flyrock
While flyrock is less of an issue with these products, it should always be assumed that a blast can throw rock. Layers of old carpet, sandbags, conveyor belts or scoops of dirt can be used to protect the blast area.
A typical blast will crack a boulder into relatively large pieces. Some rock at the center may be pulverized in this process, and this is the primary source of stray rock. Larger jobs can be protected with used tires chained together to weight down the cover material.
Bedrock may also be blasted with 1.4 cartridges, although the powder factors will be higher.
Results can be tailored to the job
A good blast will result in clean fractures and pieces ranging from 1 cubic foot to a cubic yard or so. The size of cartridges and distribution can be used to control the fragmentation.
Typical civil construction users want the rock broken into chunks that the available equipment can move, while mining operations often desire smaller material for crushing.
Ease of Storage and Transport
A simple ATF “Type 4” magazine can used for storage of these products. These can be purchased for around the price of a “Type 3” day box or constructed from job boxes and other containers.
Non-placarded transport is typically allowed for these products, as they are classed as 1.4S material.
See this article for more details on transportation of 1.4S blasting products.