Although simple in principle, cleaning silos takes some practice and preparation. Safety has to come first because multiple hazards exist, including falls, explosions, lack of oxygen, and “drowning” in liquid or finely-milled products like flour and sugar. A silo is an OSHA-defined “confined space,” meaning that workers in it have to follow standard safety procedures for enclosed areas with inherent hazards.
Proper breathing precautions must be considered where dust, volatile chemicals or oxygen scarcity can occur. Sometimes this is learned the hard way. Our firm was caught off guard once when we had a worker steam cleaning a massive vat that had held cooking oil. Steam vapor replaced the breathable air and literally lifted the available oxygen above his head. Fortunately, the matter resolved quickly, but it was a lesson in the importance of trying to anticipate the unexpected.
Silos can be cleaned by a number of methods, but in most cases, the process involves brushing down the sides of the interior and/or scraping them as needed. To avoid scratching the surface and to prevent sparking, plastic scrapers may be needed. Vacuuming is a common method of cleaning debris from the bottom. However, this can stir up a lot of static electricity around certain materials such as flour. Visible sparks can occur. A way to reduce this risk is to attach wooden poles to vacuum hoses to ground them.
Silos are normally cleaned without water. But in some instances wet cleaning is the only method available. As an example, if a flour silo needs welding, all combustible material must be removed and this may only be achievable through wet washing. This means the silo must dry out and this can cost production time. Moisture attracts mold so that is another consideration. Needless to say, the silo needs to dry thoroughly before it is refilled.
Food storage silos typically have platforms or “cages” built in at the top so workers have access for cleaning and servicing. These have to be treated with respect. Although it happens rarely, these cages can have breaks in them that can be hidden by a coating of flour or sugar. A worker should fully inspect these and ensure he’s wearing a harness and lifeline before stepping onto such an apparatus.
Sometimes you find no cage at all. It’s simply open space at the top. In this case, a worker will need to drop down from the top in a "bosun's chair", a chair on a rope that is lowered down. It may have a motor or be controlled by hand at the chair. Even eighty-foot silos may need to be cleaned this way. Any time a bosun's chair is used, it is secured on the outside of the silo and OSHA safety standards are adhered to.
Such specialized equipment, preparations and OSHA requirements prompt many companies to hire outside firms to clean their silos. It saves a lot of headaches. But some plants still prefer in-house cleaning. Whatever method is used to clean, an opening at the top of the silo is vital for access and, sometimes, ventilation. An opening at the bottom is equally critical for draining out product which has been cleaned from the silo. In some instances, there are no access doors at either end and they have to be installed.
by: Dan Stradford, CEO
Action Duct Cleaning Co., Inc.
