Protecting workers from dust means controlling exposure and having the right tools.
One of the areas that demands attention when it comes to monitoring and measuring is construction dust.
Respirable crystalline silica dust is the second biggest killer of construction workers after asbestos, according to the Health and Safety Executive (HSE). Regularly breathing construction dust can cause respiratory diseases like lung cancer, asthma, emphysema and silicosis.
Power tools used on stone create large amounts of airborne dust that may contain respirable crystalline silica, says John Saunders, principal ventilation scientist at HSE’s Health and Safety Laboratory.
“Different types of stone contain different amounts of silica,” he explains. “When you use power tools to work with stone, you will create dust that contains a wide range of particle sizes.
“Large dust particles that you can see with the naked eye will fall to the floor. Typically dust particles less than 100 microns (0.1 mm, which is relatively large) will get into your mouth and throat, causing irritation.
“But what we are particularly interested in is respirable crystalline silica, approximately less than 5 microns, which typically you will not be able to see with the naked eye. These particles are small enough to get deep inside the lung, potentially leading to serious and potentially fatal diseases.”
Reducing the risk
Employers have a legal duty to prevent or adequately control worker exposure to respirable crystalline silica dust and the HSE has workplace exposure limits on what the airborne concentrations can be over an eight-hour day. This underlines the importance of minimising the risk.
John Saunders principal ventilation scientist HSE
Effective control of exposure to dust is achieved by a number of measures. On-tool extraction is a crucial way of reducing the exposure to dust and other contaminants.
With this in mind, Hilti commissioned HSE’s laboratory to review its laboratory facilities and equipment in Kaufering, Germany, where it measures airborne dust concentrations generated when operating electric power tools.
The Hilti test laboratory conforms to the strict requirements of a new European standard – EN 50632 (electric motor operated tools – dust measurement procedure). This is divided into three parts: part one covers general test requirements, and parts two and three cover requirements for the dust measurement of particular types of tools.
“The design of extraction has not been added to the tool as an afterthought; rather, it has been embedded into the tool design at an early stage”
John Saunders, HSE
The intention of part one is to specify the procedure to measure inhalable and/or respirable dust concentrations produced by power tools under standardised conditions. While the airborne dust concentration during actual use will differ, the test allows a comparison of dust concentrations produced by tools of the same type.
EN 50632 specifies that filters used for sampling are weighed in controlled humidity conditions using a balance to a precision of 0.01 microgram – a necessary, but expensive investment (Hilti’s gravimetric measuring equipment, for example, costs €11,000). The standard also demands that the tool is used for an hour and the operation is repeated three times, with the average taken of the three dust samples collected.
Mr Saunders confirmed that the Hilti test lab in Kaufering met all these stringent requirements and commented on the inclusive approach Hilti takes to dust control with its equipment: “It’s clear that the design of extraction has not been added to the tool as an afterthought; rather, it has been embedded into the tool design at an early stage.
“This holistic approach was illustrated by the use of computational fluid dynamics (CFD) to predict flow profiles within the housing of the Hilti cutting tool (pictured, top), which are then prototyped and tested,” he says. “This cycle of CFD coupled with prototyping has allowed the extraction design to be optimised.”