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Silo cleaning - a guide to best practice

10 June 2016

Rentokil Specialist Hygiene technical manager Luke Rutterford looks at how to clean silo storage safely and to the best possible standard

Food and drinks manufacturing and processing (FDMP) in the UK is thriving, with a recent government study showing that it accounts for over 8,000 companies in Britain. Silos play a crucial role in this industry and also in agriculture, providing bulk storage for supplies such as flour, sugar, grain and animal feed. They protect the product in a stable environment to reduce the risk of spoilage from microbial growth, contamination or pest infestation. 

It is essential that high levels of silo hygiene are maintained on a regular basis, not only because of the high risk of contamination due to the volume of materials stored in silos, but also to protect the end consumer. 

Regular cleaning of silos is required to prevent the build-up of product residues on internal surfaces, which can create ideal conditions for microbial growth and the breeding of Stored Product Insects (SPIs). SPIs are responsible for the spoilage of stored commodities worldwide, causing serious problems for farmers and food manufacturers as they consume large amounts of food as they develop. This can cause a considerable reduction in the weight of the product, resulting in a major loss of revenue. In addition, SPI infested grain which is destined for human consumption can be downgraded due to physical damage and the reduced nutritional value of the commodity.  

How to clean a silo safely 

The cleaning of silos can be a challenging task, and it is important to remember that the structures must be emptied before cleaning, and so planned into downtime. When tackling these enormous structures, the health and safety of cleaning operatives is paramount, as the risk of injury or fatality is very high; ensuring the use of the correct ATEX rated intrinsically safe equipment is crucial, especially when working with dusty food stuffs such as flour, as the potential for a spark from electrical equipment to ignite dust and cause an explosion is a very real possibility, and one that is realised every year throughout the world. 

By far the most effective method for cleaning silos is to have someone inside the unit. A team of three is standard, with the entry technician being winched into the main chamber and supported by a winch man. A third person should also be on hand to record gas readings and assist in case of an emergency. The air must always be tested by gas detector before entering the silo, as it may be oxygen deficient and dangerous to enter. Ventilation is key and can make all the difference when reducing the amount of product that can stick to the sides of the silo. 

Once specialist operatives are safely in the right place, the actual process of cleaning the silo is relatively straightforward, the same as cleaning any large storage area. It involves dry brushing, scraping and the removal of waste. The only real difference is the difficulties presented by the specific commodity, sugar can set like concrete, and flour is prone to clinging onto the side of the silo creating a thick layer of flour suspended in mid-air, which can bridge across the silo and then empty beneath. The cleaning process can also result in a large quantity of dust, which can increase the cleaners’ risk of lung conditions. P3 particle masks are therefore essential for anyone conducting a silo clean. 

While the physical process of cleaning silos may be straightforward, it is recommended that specialist teams are employed. These teams will be fully trained in confined space entry, emergency escape and the correct use of appropriate equipment, and can be brought in at short notice, offering a consultative expert approach to the process. This makes commercial sense as costs are minimised, silo downtime is reduced and the risk to employees is kept as low as possible.