A spice plant fights dust, heat and its own smell
A spice plant cleans, dries, grinds, blends and packs. The grinding stage is where the building's problems concentrate: it produces heat, it produces very fine dust, and it produces a smell that carries.
Grinding heats the product and the room
Mills put a large amount of energy into a small mass. Some of it goes into size reduction and the rest becomes heat, in the product and in the air around the mill.
That heat matters twice. It degrades volatile oils, which is a quality problem, and it warms the hall, which is a comfort problem. Cooling the product and ventilating the mill room are both part of the process design, and the building has to give them somewhere to happen.
The dust is fine, combustible and everywhere
Spice dust is finer than flour dust and it stays airborne longer. It settles slowly, on top of everything, including the purlins and the roof profile where it cannot be reached.
As with any combustible dust, the two structural questions are whether relief venting is required and whether the surfaces can be cleaned. Deep roof profiles and exposed purlins fail the second question, and once dust has accumulated in them the first question becomes more serious rather than less.
The smell is a site boundary problem
Air leaving a spice plant carries the volatiles that make the product valuable. To a neighbour, the same compounds are an odour complaint, and complaints tend to arrive after the building is finished.
Exhaust that is discharged at roof level, above the building's own recirculation zone, is the cheapest mitigation. Discharging at eave level or through a wall louvre puts the air exactly where people will notice it.
Hygiene and dust control pull against each other
A food plant wants surfaces that can be washed. A dust-hazard plant wants surfaces that stay dry. In a spice plant both apply in different rooms, and the boundary between them needs a wall.
Wet cleaning in a dusty room creates the worst case: damp dust on steel, which is both a corrosion source and a hard layer that is difficult to remove. Dry cleaning by vacuum in the dusty rooms and wet cleaning only in the packing rooms is the arrangement that works.
What I want before drawings
- The process stages and where grinding, blending and packing happen.
- Whether a dust hazard assessment exists, and what relief venting it requires.
- The cleaning method for each room.
- Where exhaust air is discharged, and what is downwind of the site.
- The receiving and dispatch methods, and the vehicle sizes.
- The wind speed for the site in km/h from the applicable local code, not a round number.
Spice plants are small buildings with a high density of problems. Most of them can be solved on a plan, provided somebody asks about dust, heat and odour before the roof is ordered.
Written by Johnny Joe, who advises owners and project managers in Africa and South America on steel buildings. If this decision is live on a project, send the layout and the constraint that worries you and I will tell you what it changes.
Related: a dry grinding hall · a combustible product with fine dust · dust as a governing hazard · separating a fire load
