Metal Dust and Metal Dust Collection Overview
Metal dust may be generated during grinding, buffing, cutting, stamping and polishing operations. The size of the metal dust is based on the operation the dust is generated in. Cutting and grinding generate larger (heavier) particles than polishing and buffing.
Beryllium Disease, Hard Metal Disease and Siderosis are the most common concerns in the metal working industry. People that breathe in metal dust are at risk of these diseases and many others. Some of OSHA’s Permissible Exposure Limits (PEL’s) averaged over an 8-hour work day are:
- Cadmium: .005 mg/m3
- Beryllium: .0002 mg/m3
- Lead: .05 mg/m3
- Hexavalent Chromium: .005 mg/m3
A source capture dust collection system reduces the risk to employees and the employer.
Metal dust in the plant is not only a health hazard, but also impacts the quality of the finished product. Metal dust also affects packaging and can be both a fire and explosion hazard. Both machine, and more importantly, employee life expectancy, are lowered when exposed to metal dust.
Dust Collection System Selection
Aluminum dust and titanium dust are explosive dusts and should be handled through a wet dust collection system. Grinding applications, when possible, should be confined to a Dust Booth or down draft/ back draft tables. When the size of the products and/or work space prohibit these, a constant air filtration metal dust collection system could be considered.
The selection of the media/filter used, largely depends on the type of metal, the volume of metal dust collected, and the dust size being generated. For example, cutting recycled electrical power lines will require more filtration because you have rubber sheathing dust, lead sheathing dust and plastic.
Larger particles could be removed by a cyclone, but the finer lead particles require a final HEPA filter because of the lower exposure limit values. By comparison grinding steel could be filtered through a shaker bag unit with a MERV 14 filter rating.
Many applications in the metal working industry generate sparks. The installation of a spark shield should be considered to protect the filters if this is the case. Mixing metals in a dust collection system such as aluminum and steel is prohibited. Grounding the duct system to remove any static charge as well as using the proper fan impeller to eliminate sparks are musts in plant safety. These are only some of the factors an industrial ventilation designer should consider.
Most concerns can be addressed by following the best practices in design outlined in the NFPA 484 standard for “Combustible Dust or Metals”.