Dead finger

Did You Know?

• A reactive monitoring system for vibration exposure, based on tracking grinding disk usage, was introduced by Carl West at a fabrication workshop in Rotherham, England in 2009.
• Alice Hamilton MD discovered the link between increased HAV symptoms and cold weather during a study of quarry cutters and carvers in Bedford, Indiana in 1918, which was a particularly harsh winter.
• Side effects of hand-arm vibration can include discomfort in the head and jaw, chest and abdomen pains, and changing speech.

Hand-arm vibration syndrome

Excessive exposure to hand-arm vibrations can produce several patterns of disease collectively known as HAVS or VWF, affecting nerves, joints, muscles, blood vessels, or connective tissues of the hand and forearm. Tingling, whiteness, or numbness in the fingers may initially be mild and limited to the fingertips, but as the condition worsens the entire finger down to the knuckles can turn white and sensation may be lost. With continued exposure, periodic attacks occur in which the fingers change colour when exposed to cold: they rapidly become pale with loss of feeling, followed by an intense red flush (sometimes preceded by a dusky blue phase) that signals the return of blood flow and is often accompanied by painful throbbing. In more severe forms, attacks happen frequently in cold weather—not only at work but during leisure activities—and may last up to an hour, causing considerable pain, loss of manual dexterity, and reduced grip strength. In extreme cases the affected person may lose fingers. The effects are cumulative: symptoms may disappear after a short time initially, but if vibration exposure continues over months or years they can worsen and become permanent. Hand-arm vibration is a relatively newer occupational hazard; concern about HAVS has lagged behind that for noise and chemical hazards. The Occupational Safety and Health Administration in the United States has not yet issued official exposure action or limit values.

Occupations at risk

Occupations at risk include mining, foundry work, and especially construction. Dentistry is an unexpected field associated with HAVS, linked to frequent use of dental hand-piece tools. While men are more often affected in the working population, a significant number of women also experience HAVS. A Swedish study found that about 2% of women and 14% of men use vibrating tools for work, and women are more likely to report symptoms at a higher prevalence than men.

Suggested guidelines

The British Health and Safety Executive advises an exposure action value of 2.5 m/s² and an exposure limit value of 5.0 m/s², following a 2002 EU directive. Yet even at the action level, 10% of people would suffer sensorineural injuries within five years. The Canadian Centre for Occupational Health and Safety endorses the ACGIH threshold limit values. The National Institute for Occupational Safety and Health suggests reducing vibration exposure through engineering controls, medical surveillance, personal protective equipment, and administrative steps like limiting tool use hours and training workers on hazards and safe handling.

Damage prevention

Good industrial health and safety practice requires assessing vibration exposure in terms of acceleration, amplitude, and duration. Using a tool that vibrates slightly for a long time can be as damaging as using a heavily vibrating tool for a short time. Trigger time—the period the worker actually has a finger on the trigger—is measured in hours per day. Vibration amplitude, quoted in metres per second squared, is measured by an accelerometer on the tool or given by the manufacturer and can vary significantly with tool design, condition, and style of use. Anti-vibration gloves are made with thick, soft palm material to insulate from vibrations, but protection depends heavily on frequency range; most gloves provide no protection in the palm and wrist below about 50 Hz and in fingers below about 400 Hz. High grip force, cold hands, or shear vibration forces can reduce effectiveness or increase damage. Gloves help keep hands warm, but the tool's frequency output must match the glove's properties. Legislation in various countries has obliged equipment providers to develop better-designed, better-maintained tools and employers to train workers appropriately, and has driven innovation such as the easily manipulated mechanical arm (EMMA) and suspension mechanisms in chainsaws. In the UK, the Control of Vibration at Work Regulations 2005 governs exposure. The Health and Safety Executive provides examples such as a hammer drill varying from 6 m/s² to 25 m/s² and publishes lists of typical vibration levels and exposure time graphs, making risk management relatively straightforward.