Vibration as big an OHS threat as noise, says testing company

Finger pain, numbness and even gangrene are the symptoms of a serious occupational disease that strikes up to 50% of hand-tool users. The cause is vibration, but while the impacts are well known internationally, local testing company Noise and Vibration Measurement Systems describes its effect as a “sleeping giant” in Australian workplaces.

Noise and Vibration Measurement Systems' Stewart Wood says hand tools such as grinders could damage the health of Australia's manufacturing workers irreversibly: “Almost everyone understands the need to protect their hearing in noisy workplaces but it comes as a shock to most employers that vibration is just as hazardous.”

According to the University of Tennessee Institute for the Study of Human Vibration, 8 to 10 million workers in the US alone are exposed to occupational vibration every day. The institute explains that vibration falls into two categories:

• Whole Body Vibration (WBV), or head-to-toe exposure, typically affects truck, bus, heavy equipment, farm vehicle, forklift and overhead crane operators.
• Hand-Arm Vibration (HAV), or localised vibration exposure, mainly affects those who use vibrating pneumatic, electrical, hydraulic and petrol-powered hand tools.

Symptoms begin with tingling and/or numbness in the fingers, followed by the appearance of a single white or blanched fingertip.

“This seemingly innocuous attack of ‘white finger' marks the beginning of the dreadful later irreversible finger blanching process,” write the institute’s researchers, Wasserman and Wasserman, in an overview of the syndrome. “Often these attacks are mistaken by workers who think they have frostbite.”

Early attacks of finger blanching last about 5-15 minutes and are widely spaced apart. With continuing exposure to vibration, the attacks increase rapidly in number, intensity, duration and finger pain, especially in cold conditions. Touching cold objects such as a vehicle steering wheel early in the morning, or cold water striking the fingers, becomes painful. In the later stages, attacks occur in all seasons and off the job as well as at work.

The simultaneous combination of vibration, cold and smoking is “particularly deadly”, says the institute, since all three help to close down blood vessels. In extreme conditions, the loss of blood supply to the fingers can lead to gangrene, which may require amputation.

While the symptoms of HAV Syndrome are clear, measurement is more complex. The International Standards, ISO 2631 and ISO 5349, that define how vibration exposure is assessed stipulate that the three axes - x, y, and z - must be taken into account because the human body reacts differently to horizontal and vertical vibration.

Apart from direction, the other three characteristics of vibration must be measured: magnitude, frequency and duration. Western Australia’s SafetyLine Institute last year issued a human vibration guide detailing each of the characteristics.

Magnitude represents the acceleration of the oscillating objects, expressed in units of metres per second squared (m/s²). Unlike other hazards, frequency refers not to the occurrence of vibration but to the motion itself. Because each part of the human body has its own natural frequency, different vibration frequencies have differing impacts across the body.

The SafetyLine guide and ISO standards include complex algorithms for the calculation of exposure. Noise and Vibration Measurement Systems runs one-day courses for workplaces to control the risk of vibration-related injuries and in the use of pocket analysers that are typically deployed to sample the vibration workers are exposed to during different tasks.

“Annex B of the EU's HAV Good Practice Guide shows just how much variation there is in vibration caused by pieces of equipment,” Wood says. “The total vibration figures for grinders, for example, range from just over 2 m/s² to nearly 30 m/s². It’s important to sample the vibration caused by each piece of equipment performing each task with each type of material, to assess the risks different tasks present and implement controls.