Blast fume is the orange or brown cloud that sometimes rises after a shot. It is nitrogen dioxide, it is toxic, and Queensland treats a cloud that leaves the blast exclusion zone as a reportable event. QGN 20, the guidance note on the management of oxides of nitrogen in open cut blasting, sets out how to manage it and exactly what to record when it happens.
This guide covers why fume forms, what counts as a fume event, the data you have minutes to capture, who to report it to, and why the exclusion zone you already use is not designed for gas.
Why fume forms
Blasting explosives predominantly use ammonium nitrate. Detonated under ideal conditions, the reaction is close to complete and the gaseous products are largely benign. Field conditions are not ideal conditions.
When the reaction runs inefficiently, oxides of nitrogen are produced instead. The most harmful is nitrogen dioxide, and it announces itself with an orange to brown cloud. In QGN 20’s terms, fume means the oxides of nitrogen, particularly NO2 as the most prevalent.
The variables that drive it are the ordinary variables of a blast: the explosive formulation and its oxygen balance, water in the hole and product sleep time, ground conditions and the presence of reactive ground, confinement and stemming, hole diameter and loading practice, and initiation timing. Most fume events trace back to a combination rather than a single cause, which is why investigating them as “someone did something wrong” usually fails.
What counts as a fume event
QGN 20 defines a fume event as an event that generates visible nitrogen dioxide that moves outside the standard blast exclusion zone.
That definition carries a warning inside it that is worth stating plainly. The standard blast exclusion zone is designed to protect people from projections and blast overpressure. It is a distance calculated for flyrock and air blast. It was never designed as a gas exclusion distance, and gas does not behave like flyrock: it drifts, it follows terrain, it concentrates in low ground, and it goes where the wind takes it.
So the fact that a cloud reached the boundary of a zone that was adequate for projectiles tells you nothing reassuring. It is the trigger for a report precisely because the zone was not sized for that hazard. Sites that manage fume well set a separate, meteorologically informed standoff for gas, and adjust it on the day. The general principles of exclusion and clearance are covered in blast exclusion zones, flyrock and clearance.
The exposure standard
The objective of fume management is that nobody is exposed to nitrogen dioxide above the short term exposure limit of 5 parts per million.
Nitrogen dioxide is deceptive in the field. It has a sharp odour, but olfactory fatigue sets in quickly, so the smell disappears while the gas does not. The serious effect is delayed: a person can walk out of a cloud feeling only mild irritation and deteriorate hours later with pulmonary oedema. Anyone with a meaningful exposure needs medical assessment and observation even if they feel well, and the time of the exposure and the symptoms observed at presentation are part of what the clinician needs.
That delay is the reason fume is treated as a reportable event rather than as a nuisance. The consequence is not visible at the time it needs to be acted on.
What you must record, at the time
If a fume cloud travels outside the designated blast exclusion zone, it must be reported to both the Explosives Inspectorate and the Mines Inspectorate. QGN 20 sets out the information to provide, and this is where the practical difficulty sits, because most of it is perishable.
- Time of the event.
- Fume strength rating, 0 to 5, determined when the cloud is at its highest concentration, using the NOx rating scale in the guidance note.
- Percentage of the blast area emitting fume, in 10 per cent increments, or the AEISG A to C rating.
- Size of the NOx cloud in metres, as width, length and height.
- Wind speed and direction.
- Stability class of the atmosphere.
- Temperature.
- Cloud cover.
Read that list again with a stopwatch running. The rating has to be judged at peak concentration, which lasts seconds. The cloud dimensions have to be estimated while it is still coherent. The meteorological conditions are the conditions at the moment of the shot, not the conditions when someone gets back to the office.
A fume report assembled the following morning from memory and a weather website is a reconstruction. It may satisfy the reporting obligation. It will not support an investigation into why the shot fumed, and it is useless for trending across a year of blasts.
Managing fume before the shot
- Product selection matched to ground conditions. Formulations can be adjusted to reduce fume potential within their category, and the product needs to be fit for the purpose it is actually being used for.
- Water management and sleep time. Water in the hole and product left loaded too long are two of the most reliable predictors of a fume event.
- Reactive ground identification. Known reactive ground changes the product, the loading practice and the sleep time limits.
- Stemming quality and confinement. Poor confinement is inefficient detonation, and inefficient detonation is fume.
- Meteorological assessment on the day. Wind direction and atmospheric stability decide where a cloud goes. A stable inversion layer will hold gas at ground level and carry it a long way.
- An adjusted exclusion zone for gas, separate from the projection zone, based on those conditions.
- Accounting for people by name, including anyone downwind outside the projection zone who would not normally be cleared.
Where sites come unstuck
- The gas zone equals the projection zone. The single most common structural error, and the definition of a fume event exists because of it.
- The record is made later. Perishable data reconstructed from memory, which fails both the investigation and the trend.
- Fume is treated as an environmental complaint. It becomes a community relations issue instead of an exposure event, and the health follow up does not happen.
- No trending. Individual events are reported and closed, and nobody looks at 40 shots together to find the pattern in ground type, product, sleep time or season.
- People downwind are not accounted for. The blast crew is cleared. A dozer operator two ridges away, outside the projection zone, is not.
- Nobody records the shots that did not fume. Without the negative cases there is no baseline, and the analysis has nothing to compare against.
Capturing fume data where it happens
Fume is the clearest example on a mine site of a record that has to be made in the field, in the moment, or not at all. It is also a record with real long term value, because the pattern only emerges across dozens of shots.
This is what HazView is built to do. A gas check or fume observation is recorded at the blast, on the map, with the time it was taken, the person who took it, the rating, the conditions and photographs of the cloud attached. It is held permanently, so a fume event from four years ago is still there with its photographs and its meteorological conditions intact when someone asks whether this ground has fumed before.
Because the records are structured and located rather than sitting in a document, they can be trended. Fume ratings against ground type, against product, against sleep time, against season. That is the analysis that changes blast design, and it is impossible when each event lives in its own report.
The REST API matters here too. Blast designs, product and loading data usually live in a drill and blast system, and monitoring data may come from elsewhere. Those can be brought in against the same blast, and the resulting records pushed back out to whatever the business reports from, so nobody is retyping a fume report into a second system at nine o’clock at night.
The platform does not measure gas concentration and does not decide whether a shot is safe to fire. Those are the shotfirer’s and the SSE’s calls, with instruments. What it removes is the gap between the observation and the record.
See how HazView works for blast crews, or book a demo.
Related guides
- Recognised Standards for Queensland Open Cut Coal Mines
- Tailings Storage Facility Management
- RS11: Training in Coal Mines
- RS10: Mine Surveying and Drafting
- All QLD Open Cut Coal guides
Frequently asked questions
What is a fume event?
Under QGN 20, an event that generates visible nitrogen dioxide that moves outside the standard blast exclusion zone. The orange or brown colour is the identifying feature.
Who do I report a fume event to in Queensland?
Both the Explosives Inspectorate and the Mines Inspectorate, with the time, the 0 to 5 fume rating at peak concentration, the percentage of the blast area emitting fume, the cloud dimensions, wind speed and direction, atmospheric stability class, temperature and cloud cover.
What is the exposure limit for nitrogen dioxide?
The objective of fume management is that people are not exposed above a short term exposure limit of 5 ppm. Effects can be delayed by hours, so anyone with a meaningful exposure needs medical assessment even if they feel fine.
Is the blast exclusion zone enough to protect against fume?
No, and that is the point of the definition. The standard exclusion zone is designed for projections and overpressure. Gas drifts with the wind and settles in low ground, so a separate standoff based on the day’s conditions is needed.
Which legislation applies to blasting fume in Queensland?
Three Acts operate on a mine site using explosives: the Mining and Quarrying Safety and Health Act 1999, the Coal Mining Safety and Health Act 1999 and the Explosives Act 1999. All explosives used in Queensland must be authorised under the Explosives Act.
How long should fume records be kept?
Longer than any minimum requires. Fume behaviour correlates with ground conditions that repeat over years, so records that survive only as long as a retention policy demands destroy the only dataset capable of predicting the next event.