What does ‘Nuisance Dust’ mean?
Nuisance dust is a term that is used to describe any airborne liquid or solid, that is not harmful to the human body if the levels of concentration in the air and the duration of exposure to the environment are kept below a specific level.
Dust particles resulting in nuisance effects are typically in the coarse, PM10-2.5, and Total Suspended Particle (TSP) size fractions, and are formed through mechanical and abrasive processes. However, some particles less than 2.5 microns in diameter may occur as a result of particular activities. Particles may become elevated as a result of natural processes such as winds or man-made activities including mechanical interactions such as transportation or the tilling of land.
Examples of sources of dust nuisance in New Zealand include vehicle movement on unpaved (gravel/metal) roads, quarrying, aggregate crushing, stockpiling of materials, tilling of land, erosion of soils and riverbeds, construction sites and abrasive blasting. In some areas, high levels of pollen have been reported as an air quality concern.
In the workplace, employees may be required to work in, or be exposed to, environments that contain nuisance dust. Fulton Hogan takes the responsibility to provide a safe environment and protect the employee from illness or harm very seriously, by ensuring that nuisance dust levels are controlled and respiratory protection equipment (if needed) is supplied. All our quarry sites must comply with workplace standards for air quality set by Worksafe New Zealand. The acceptable dust levels around our quarry sites are determined by the territorial authorities, in this instance Environment Canterbury, Christchurch City Council and Selwyn District Council. Whilst the Canterbury District Health Board also takes an interest in the monitoring. Factors that are taken into consideration are the particulate size and type, the concentration of the particulate in a given area and the duration of exposure to the particulate.
General council rules and consents include conditions such as “no dust beyond the boundary which causes an offensive or objectionable effect”.
Dust is generated from 3 primary points. The crushing process itself, truck movements, and general open areas.
How do we mitigate these issues at the Fulton Hogan plants?
1. Crushing process:
Fulton Hogan uses foggers; a dust suppression system using water. The tiny water droplets absorb even the smallest dust particles in the air. These are installed on both the Miners Road and Mcleans Island plants. Also, we locate the plant centrally within the quarry, away from the boundaries.
2. Truck movements:
We chip seal the main haul roads and use water carts for the remainder of the quarry and we have speed limits within our sites of 30 kilometers per hour. The Christchurch quarries have a fleet of four 20,000 litre water carts, for use in our quarry sites and retail yards.
3. General open area:
We limit the open area through progressive rehabilitation (grassing) and clean filling of open area, we also cover the open area with clean rounds (doesn’t generate dust).
4. Above and beyond
Fulton Hogan has dust monitoring equipment at all of our operations. Roberts Road is continuous monitoring. We undertake personal tests on quarry staff yearly. It is expected that there will be a Quarry Code of Practice Programme established in Canterbury shortly, with Fulton Hogan progressively moving towards more automated dust suppression systems.