Health & Safety
Achieve clarity with fog
Fogging: a vital tool in the dust suppression armoury – an overview from
Robin Travis at Renby
The processing of bulk solids inevitably generates fugitive dust occurs in most mineral products such as:
at some stage in the production cycle. There are many Rock and sand
processes where it is not possible to contain dust at all stages Concrete, cement, and mortar
and the escape of fugitive dust becomes inevitable. Persistent Topsoil
offenders will receive closure notices from the Environment Granite, sandstone, and slate
Agency or punitive damages from employee health claims. Masonry, bricks, and tile
Doing nothing will result in company closure and is not an Asphalt (containing rock and stone)
option. Strict legislation is now in place setting tight limits to the
workplace exposure to silica. When the exposure level figure of
0.1mg/m
3
was set in 2006, it was seen by industry as being a
challenge to meet. After taking traditional steps to contain dust,
the levels were often still too high. Several years on, now that
companies are managing to achieve this level, there are further
plans to reduce the level to 0.05 mg/m
3
. A moving vehicle e.g. a
fork lift truck can raise enough dust to breach the exposure
limit. A fogging system over such fork lift truck routes would
control this.
It is not just silica that is the problem. There are pressures
now to increase the burning of wood to generate energy. Some
fast rotation coppice woods have particularly hazardous dust that
has microscopic hooks on the surface that lodge the particle into
the lungs. With regular lorry loads delivering materials,
warehouses rapidly fill with dust. Diseases similar to silicosis will
result if steps are not taken to protect the workforce. By fogging
the reception area, the dust can be eliminated.
All of these conditions lead to potential health problems
down the line for the work force. Doing nothing in the short
term is a false economy as a company is leaving itself open to
future claims. In an increasingly litigious society, these claims
will come, in some cases, years after the event. Many
companies were put out of business by asbestosis claims.
Typical Fogging Nozzle with Push Fit Fittings Why put your company at risk of claims due to silicosis and
other respiratory diseases?
Why is Dust a Problem? Fog must form a part of the strategy to achieve the required
There are many traditional ways of controlling dust, but a new, legislated minimum exposure levels.
proven and cost effective technique is to use fog to remove dust
from the air. The name fog is just what it implies – small What is fog?
droplets of water injected into the air. If the fog is generated in Fogging works by releasing very small droplets of water into the
the right way, the energy required can be very low – between 1 air. Airborne dust particles adhere to the water droplet and
to 2 kW for a large warehouse – giving considerable operating agglomerate. Once several have agglomerated together they
cost savings when compared to the 25kW+ power consumption become heavy enough to fall out of the air. The water droplet
of fans on a comparable dust collector. size is very important. If the droplet is too large, say 50
Some years ago, a dusty work environment was not seen as microns+, the dust particle will bounce off the water droplet
much of an issue, unless the dust was explosive or toxic. This is surface tension and remain airborne. To achieve a useful dust
no longer the case. In a dusty environment, machinery will fail suppression effect, the droplets need to have a mean diameter
sooner as bearings wear out and motors overheat. The plant will in the region of 10 to 15 microns i.e a similar size and mass to
also waste valuable energy due to the loss of efficiency, thereby the respirable dust particles.
giving an unnecessary increase in operating costs. It is important not to be misled by sprinkler systems operating
There are also proven links between inhaled silica dust and at typical water main pressures of c. 6 Bar. The droplet sizes are
silicosis, a condition that is very similar to asbestosis. Silica often in excess of 100 microns and it is quite common to
42 Solids & Bulk Handling February 2010 www.solidsandbulk.co.uk
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