Reducing-risk-NOx-fume-exposure-during-blasting (ppt).pdf

7/27/2019 Reducing-risk-NOx-fume-exposure-during-blasting (ppt).pdf

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Reducing the Risk of NOx FumeExposure during Blasting


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Major Fume Events

Recently, Downer EDI Blasting services has had some success in reducingthe generation of NOx fume from open cut blasting activities.

60 blasts that were reported to have generated fume within the scope ofDowner Blastings Qld

Many of these have been thoroughly

investigated to determine the root cause


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Causes of fume from blasts

9 Emulsion formulation deficient in oil content or rich in ammonium nitratecontent (Oxygen rich).

9 Poor diesel absorption by ammonium nitrate prill.

9 Water ingress in products as the product exceeds sleep time limits.

9 Critical density of product.

9 Poor hose handling practices (top loading product into blast holes).


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Causes of fume from blasts

9 Critical diameterfor product.

9 Product desensitisation by pressure.

9 Ground conditions such as presence of cavities / cracked ground.

9 Presence of dynamic water.

9 Lack of proper product confinement (including proper stemming)

9 Direct contact of incompatible chemical compounds


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Common links between major events

There is no one decisive factor that will ensure the generation of NOxwithin the blast process.

There was however some common links that increased the likelihood ofNOx fume within any blast. These included:-

Any product that is manufactured and loaded that is outside the

optimal product specifications (AN prill, AN Emulsions and gassingagents)

Dynamic water (regardless of product)

Excessive sleep time

Unfavourable ground conditions (cavities, hardness)


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Bringing it together.

The engineering phase should consider (at least), the following aspects ofthe any blast:-

The blast outcomes The method of blast relief (vertical / free face)

Area to be blasted The geological structure and rock strength of the area to be blasted The pattern dimensions

The product available The amount of explosives required to blast the area (P/F) Water content Blasthole conditions

Time / weather Timing


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Matching the ground conditions to thePowder factor

Several of the major fume events have been found to have apowder factor that was significantly higher than required for the

ground conditions.

This is often the result of:-

A lack of understanding of the ground conditions

Changing the product selection Inappropriate drilling techniques / blast patterns / drill data

Areas of any blast, that are over blasted are much more likely to

produce a major fume event than areas of the blast pattern thatare not as heavily loaded.


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An example

During one blast / fume event, the root cause was attributed to thefollowing:-

There was no definitive geotechnical data available relating to either thecondition of the rock or the rock strength.

The designed powder factor was listed as 0.53, but from historical data, areasonable powder factor was in the range of 0.3 to 0.45.

A product change product the powder factor to 0.61

This is an actual energy rating increase of 47.5%

increase applied to the same ground area

This was combined with a vertical displacementrelief / loss of confinement and product column

decoupling.


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An second example

During a second blast / fume event, the root cause was attributed to thefollowing:-

Incomplete combustion reaction and due to the ingress of water or mudinto the product column. (rain event)

There was no definitive geotechnical data relating to either the conditionof the rock within the explosives loading area (voids, cavities, fracturesand faults) or the rock strength.

The area was identified to be composed of wet clays and the compression

strength of the material in this area is low with a reasonable powder factorcould be estimated to be in the range of 0.3 to 0.45.

The application of a designed energy levels(0.68 powder factor) to an area of soft / wet

clays has resulted in the generation of NOxand carbon mono-oxide fumes through a lossof confinement and product column decoupling.

If d h t l did ll t h t


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If you do what you always did, youll get what youalways got...

DBS has recommended to the relevant sites that:-

Revise the use of standard pattern sizes during the wet part of the year.

Engage a lower powder factor for areas of mine sites where the

geological structure is predominately of a soft rock / clay structure.

In areas where the geological structure is predominately of a soft rock /clay structure minimise the sleep times

Engage a free face blasting to provide the appropriate burden relief asopposed to other designs

The use of deck loading where a productselection has changed from Anfo to Heavy Anfo.

Consider the development of blast parameters forparticular parts of mine sites.


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The Result???

Very encouraging with a decrease in both frequency and intensity of NOxfume event from the same areas of the same mine sites that has seen

significant fume events previously

Fume events are still a concern but thereduction in risk to all personnel on site(s),

through the management of some key blastengineering aspects, is providing asafer work place for all.


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Other steps taken to minimize NOx exposureson sites

Ensure that the mine site has:-

A suitable process to notify neighbours of blasting activities

A fume monitoring programs for the neighbouring mine sites are inplace

Hard controls barriers such as the use of suitable gas monitors, blastguard positioning and communication

A process that enables the estimation of the travel and spread of acredible fume event prior to the firing of the shot (e.g:- GPS compassand wind meter)

A process to sample blasting activities on site to establish base line data(fume reporting)

A suitable plume modelling / tracking process.


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Other steps taken to minimize NOxexposures


A suitable risk assessment for Blast Controlling (including fumemanagement)

A suitable document detailing obligations of persons performing the roleof Blast Controller (in regards to fume management)

Assessed and implemented a minimum blast exclusion zone

Ensure that all persons involved in a blast as either Blast Controllers /Blast Guards and / or Shotfirers are deemed as competent persons inregards to their role on site.


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Other steps taken to minimize NOxexposures


A process to video all blasts to capture any fume event includingtracking of the fume cloud pathway.

A site specific proforma letter to the treating physician to assist indiagnosis of persons exposed to oxides of nitrogen (NOx)

A pre-shift meeting document that includes a particular section relatingblasting information including proposed firing time, blast location,

expected blast affects and control measures, and exclusion zones /marker locations

Reviewed the site procedure for Toxic Gasses on site and include asupporting procedure for the Management of Post Blast (NOx) Fume.


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The aim of this presentation was simply to share our experiences withall of you!

Thank You

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