Thursday, January 24, 2013

On the Job Toolbox Talks - Trenching and Excavation

According to the Bureau of Labor Statistics, in the United States between 2000 and 2009, 350 workers died in excavation or trench collapses. Trenching operations usually include water, sewer, pipeline, communications or power line construction. One study indicated 64% of fatalities occurred in excavations of less than 10 feet (3 meters). In addition to collapses, trenching operation hazards include: falls; falling objects from above and hazardous atmospheres. Prior to any trenching or excavation, local utility companies should be contacted to locate and identify any underground cables, pipes, tunnels or tanks that may be in the excavation area. “Pot-hole” to determine their exact location prior to digging.

Trench Depths
• Less than 5 feet (1.5 meters) - A competent person should review the excavation soil and plans and determine if a protective system as described below is required.
• 5 feet (1.5 meters) to less than 20 feet (6.1 meters) - a protective system must be in place unless a competent person has determined that the excavation is entirely in solid, stable rock with no potential for cave-in.
• 20 feet or greater – a protective system designed and approved by a registered professional engineer must be installed.

Competent Person
A person trained in trenching and excavation safety should inspect the excavation daily. The inspection should berepeated if conditions change (e.g. after rain fall, freeze/thaw weather changes). The competent person should be
authorized to order immediate corrective action, including restricting entry into the excavation, until any hazards orpotential hazards have been eliminated.

Protective Systems to prevent cave-ins
• Benching – excavating the sides of an excavation to form one or more horizontal levels or steps (1)
• Sloping – Cutting back the trench wall at an angle away from the excavation. (2)
• Shoring – Installing a support system of using materials such as posts, beams, planking and hydraulic jacks tosupport or “shore up” the sides of the excavation. (3)
• Shielding - Using trench boxes or similar enclosures to prevent cave-ins. (4)
• Refer to ANSI A12.10-1998 for specific design requirements.

Other safety requirements
• Keep heavy equipment away from the sides of the excavation
• Keep spoils piles at least 2 feet (1 meter) away from the trench edge. (5)
• For excavations deeper than 4 feet – conduct air monitoring similar to confined space entry – oxygen,combustibles, and toxic gases/vapors.
• Ladders, steps, or ramps must be provided for safe exiting from the trench. An exit point must always be within
25 feet of all workers at all times. These may need to be continuously relocated as the job progresses. (6)
• Ensure workers are trained on work hazards and proper work practices.
• Develop a trench emergency action plan and train workers and supervisors on the proper actions to take in an
emergency.

View Steps 1-6  

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Wednesday, January 16, 2013

Hand and Arm Vibration Syndrome (HAVS)

Hand and Arm Vibration Syndrome (HAVS) has been known for almost 100 years. It is referred to by various names: Raynaud's phenomenon, vibration white finger, dead finger and vibration syndrome. HAVS can affect upwards of 50% of people who use vibrating tools. While it is unclear exactly how many workers actually suffer from vibration syndrome, current numbers are thought to significantly underestimate the situation.

Who is affected?
Research indicates a linear relationship between vibration dose (level of vibration and years of exposure) and onset/severity of HAVS. In the construction trades, HAVS most commonly occurs in: Pavement breakers; Nut runners; Chainsaws; Grinders; Riveters; Air drills; Chippers; Compactors. HAVS usually requires several hours exposure each day for several months or years before first signs develop.

What are the signs and symptoms?
Early stages usually include episodic numbness, tingling and blanching of fingers. Pain in response to cold exposure may occur. The symptoms are intermittent at first. With increased exposure, however, attacks become more frequent and more severe. Recovery is usually painful. As HAVS progresses workers may notice reduced grip strength and manual dexterity. Early stages are usually reversible.
As the disease progresses symptoms include: Loss of circulation to fingers; Continued loss of manual dexterity; Gangrene and tissue necrosis. It is thought that vibration somehow causes direct damage to nerve endings. Advanced stages are progressive with minimal effective treatment.

How can HAVS be prevented?
Low (anti-vibration - A/V) vibration tools. Some tools are designed to be anti-vibration tools. This needs to be designed into tool from the start. Retro fit of tools is difficult and only works on rare occasions.

Work practices
One cost effective method is to minimize grip force (minimize coupling) on the tool. Hold the tool as loosely as possible and still control the tool. Other methods include: Use weight of tool to hold it against the work piece; Slip resistant handle to reduce grip force; Reduce the duration the tool is used; Use minimum speed or impact force that still allows job to get done efficiently; Provide work breaks to avoid constant exposure. Avoid allowing the hands to get wet and cold as this can further reduce circulation to the fingers.

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Sources: Occupational Exposure to Hand-Arm Vibration DHHS (NIOSH)

Monday, January 7, 2013

On the Job ToolBox Safety Talks - Facts about Noise

Measuring Noise
Noise hazard depends on the level (sometimes called intensity) of the noise, its duration, and how often the exposure occurs. The point above which regular exposure to sounds becomes hazardous is a level of about 85 decibels (abbreviated dB, or sometimes dBA which is the value that more closely corresponds to human hearing). Noise is measured using a sound level meter.

You Don’t Get “Used to Noise”

Noise does not have to be uncomfortably loud, or even painful, to be damaging. You may think your ears are “used to the noise,” but what has probably happened is that your hearing has been temporarily dulled or that hearing loss has already begun.

A Rule of Thumb
When you feel the need to shout in order to be heard three feet away, the noise levels are probably 85 dBA or more and hearing protectors are recommended.

Using Your Ears to Assess Noise Risk

If, after the noise stops, you notice a ringing, buzzing, or whistling in your ears that wasn’t there before, this is a warning indicator. Called tinnitus, this is like a “sunburn” of the nerve cells of your inner ear, indicating that they have been irritated and overworked. Tinnitus is especially noticeable in a quiet place, such as when you are trying to go to sleep at night. If you don’t protect your ears from noise, tinnitus can become a permanent, constant annoyance in your life. Apparent muffling or softening of sounds after noise exposure is a warning sign that your hearing is affected by a temporary threshold shift. Repeatedly exposing your ears to loud noise without protection can cause the shift to worsen and become permanent, resulting in untreatable damage to your hearing ability.
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Provided by:
3M Occupational Health & Environmental Safety

Wednesday, January 2, 2013

On the Job Tool Box Safety Talks - Whole Body Vibration

Adverse affects of whole body vibration range from simple fatigue to motion sickness, low back pain, degeneration of the lumbar spinal system and herniated disks. Whole body vibration can also cause psychological irritation. All of these things create health and safety hazards for construction workers.

It is thought whole body vibration causes reduced blood flow to the spine which in turn may cause the adverse reactions noted above. Vibration may also cause continuous compression and stretching of spine resulting in structural fatigue or micro-trauma.

Control Techniques
There are three basic means to control whole body vibration exposure.

1. Eliminating the source of vibration - either modifications to the machinery to reduce vibration, or for vehicles, smoothing of the work surface.

2. Disrupting the path of vibration transmission
• Vehicle suspension - this can be of limited use for heavy haul vehicles as they usually
need tight suspensions which increase vibration transmission
• Installation of an independent suspension for cabs of vehicles
• Proper tire inflation
• Seats
i. Adjustable seat back and pan, lumbar support, arm rest
ii. Regular preventive maintenance on seats
iii. A/V seats are commercially available - but use caution in retrofitting seats into
cabs without an assessment of vehicle vibration characteristics. Amplification of
vibration can occur if the wrong seat characteristics are selected.

3. Training
• Need for, and how to adjust seats in cab
• Avoid bending or twisting spine after exposure (use simple motions to get out of cab)
• Avoid heavy lifting right after exposure

Provided by Liberty Mutual Insurance Group

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