Published Date: July 01, 2009
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Section 310 Safeguards
Employers provide safeguards that eliminate contact by workers with the categories of hazard listed in the section. Written as a performance standard, the section requires that some type of safeguard be provided but does not specify its design or how it should be implemented.
In meeting the requirement, employers must recognize the hazards to workers resulting from the design, location and nature of powered machinery or energy sources. Employers must also understand how close workers get to the hazards and what they are doing while there.
Crushed hands and arms, severed fingers, irreversible eye injuries – these are injuries preventable through appropriate safeguarding of machines and equipment. Any machine part, function or process that may cause injury must be safeguarded. When the operation of a machine or accidental contact with it can injure the operator or other workers in the vicinity, the hazards must be eliminated or controlled.
Where mechanical hazards occur
Dangerous moving parts in three basic areas require safeguarding:
(1) the point of operation – that point where work such as cutting, shaping, boring, etc. is done on the material;
(2) power transmission apparatus – all components of the mechanical system that transmit energy to the part of the machine performing the work. These components include flywheels, bullwheels, pulleys, belts, connecting rods, couplings, cams, spindles, chains, cranks and gears; and
(3) other moving parts – all parts of the machine that move while the machine is working. These can include reciprocating, rotating, and transverse moving parts, as well as feed mechanisms and auxiliary parts of the machine.
Hazardous mechanical motions and actions
A variety of mechanical motions and actions can present hazards to workers. These can include the movement of rotating members, reciprocating arms, moving belts, meshing gears, cutting teeth, and any parts that impact or shear. The basic types of hazardous mechanical motions and actions that must be recognized are:
(a) rotating, including in-running nip points – even smooth, slowly rotating shafts can grip clothing, and through mere skin contact, force an arm or hand into a dangerous position. Injuries due to contact with rotating parts can be severe (see Figures 22.1 through Figure 22.4)
Figure 22.1 Examples of hazardous projections on rotating parts
Figure 22.2 Common nip points on rotating machinery
Figure 22.3 Nip points between rotating parts and parts with linear motion
Figure 22.4 Nip points between rotating machine components
(b) reciprocating – during back-and-forth or up-and-down motion, a worker may be struck or caught between moving and stationary parts (see Figure 22.5)
Figure 22.5 Hazardous reciprocating motion
(c) transverse – movement in a straight, continuous line creates a hazard because a worker may be struck or caught in a pinch or shear point by the moving part (see Figure 22.6)
Figure 22.6 Example of transverse motion
(a) cutting – may involve rotating, reciprocating or transverse motion. The danger of this action is at the point of operation where finger, arm and body injuries can occur and where flying chips or scrap material can strike the head, particularly in the eyes or face. Such hazards are present at the point of operation in cutting wood, metal, or other materials. Examples of machinery involving cutting hazards include bandsaws, circular saws, boring or drilling machines, lathes and milling machines (see Figure 22.7)
Figure 22.7 Examples of cutting hazards
(b) punching – occurs when power is applied to a ram for the purpose of blanking, drawing, or stamping metal or other materials. The danger of this type of action occurs at the point of operation where material is inserted, held, and withdrawn by hand, as may be the case with power or punch presses (see Figure 22.8)
Figure 22.8 Typical punching operation
(c) shearing – involves applying power to a ram or knife to trim or shear metal or other materials. A hazard is present at the point of operation where stock is inserted, held and withdrawn. Examples of machines used for shearing operations are mechanically, hydraulically or pneumatically powered shears (see Figure 22.9)
Figure 22.9 Example of shearing operation
(d) bending – occurs when power is applied to a ram to draw or stamp metal or other materials. A hazard is present at the point of operation where material is inserted, held and withdrawn. Equipment that uses bending action includes power presses, press brakes and tubing benders (see Figure 22.10)
Figure 22.10 Example of bending operation
General requirements for all safeguards
All safeguards should do the following:
(a) prevent contact – the safeguard must prevent the worker’s hands, arms and any other part of the body from making contact with dangerous moving parts. A good safeguarding system eliminates the possibility of the operator or another worker placing parts of their bodies near hazardous moving parts;
(b) be secure – workers should not be able to easily remove or tamper with the safeguard. Guards and safety devices must be able to withstand conditions of normal use;
(c) protect moving parts from the entry of falling objects – the safeguard should ensure that objects such as tools and materials cannot fall into moving parts;
(d) create no new hazards – a safeguard must not create a hazard of its own such as a shear point, a jagged edge, or an unfinished surface that can cause a cut. The edges of guards for example, should be rolled or bolted in such a way as to eliminate sharp edges;
(e) create no interference – any safeguard that prevents workers from doing their work quickly and comfortably may soon be overridden, ignored or disabled; and
(f) permit safe lubrication – if possible, workers should be able to lubricate the machine without having to remove safeguards. Locate oil reservoirs outside the guard, with a line leading to the lubrication point.
Methods of guarding equipment and machinery
The following are examples of six commonly used methods of guarding equipment and machinery:
(1) Fixed or barrier guard that encloses hazardous parts
- can be used in cases where access to the hazardous parts is not required
- the enclosure permanently guards the hazardous part(s)
Figure 22.10.1 Fixed or barrier guard
(2) Moveable guard with interlock switch
- can be used where access to moving parts is required
- the moveable guard is interlocked, often mechanically or electrically, to the machine’s power source. When the guard door is opened, the machine loses power – hazardous parts stop moving or the entire machine stops
Figure 22.10.2 Moveable guard with interlock switch
(3) Two-hand control
- to prevent a hand from being caught in the machine, two start or process control buttons have to be operated at the same time to allow the machine to run
- the operator’s hands cannot be in the machine and at the control at the same time
Figure 22.10.3 Two hand controls
(4) Infrared light curtains
- a “curtain” of harmless light beams run in front of the hazardous area
- if a beam is blocked or interrupted, a control circuit senses this and shuts off power to the moving parts or the entire machine
Figure 22.10.4 Infrared light curtains
(5) Pressure sensitive safety mats
- these mats are used to guard a machine by controlling access to the machine while it is running
- mats are placed around the hazardous area and are electrically connected to the machine’s control circuits
- an operator’s footstep on a mat triggers a pressure-sensing circuit to cut power to the machine
Figure 22.10.5 Pressure sensitive safety mats
(6) Pressure sensitive edges
- flexible edging strips, electrically connected to the guarded device’s control circuits, can be added to a moving part such as a powered door or moving machine table
- if the moving part hits the operator, or the operator hits the edge, the edging strip deforms and a stop signal is sent to the power source
Figure 22.10.6 Pressure-sensitive edges
For more information
|Best Practice on Conveyor Safety|
|Concepts and Techniques of Machine Safeguarding|
|MSHA’s Guide to Equipment Guarding|
U.S. Department of Labor, Mine Safety and Health Administration
This subsection permits the use of alternate measures where enclosing or barricading a hazard is inappropriate or undesirable. The measures listed are intended to interrupt the process when the worker approaches the hazard, or to restrain or prevent the worker from coming into contact with the hazards listed.
Subsections 310(4) and 310(5)
Situations arise in which equipment is used in a manner never envisioned at the time that it and its safeguards were originally designed. Situations also arise in which, because of the nature of the work, the work cannot be performed with the guard in place e.g. performing particular types of cuts with a table saw, using an angle grinder in a very tight space.
Removing a guard in order to perform work is always the least desirable option. Consider the following angle grinder example. Its principle can be generalized to all situations in which an employer wishes to remove a guard:
Before removing the angle grinder’s guard, the employer should first try
(a) using a grinder with a smaller diameter grinding wheel – Are we using the correct size of tool?,
(b) using a die or pencil grinder that fits into a tighter space – Are we using the correct tool for the task?, and
(c) using some other type of work method – Can we alter the fabrication or finishing process so that we can still use the original tool or make its use unnecessary? Can we redesign the workpiece so that we can still use the original tool or make its use unnecessary?
If the employer determines that an effective safeguard cannot be provided, then the employer may use an alternative mechanism, system, or change in work procedure in place of the safeguard. If an employer uses this option, the alternative approach must offer workers a level of protection that is equal to or greater than the protection required by subsection 310(3). An employer should be able to explain why an effective safeguard could not be provided and justify how the alternative approach provides an “equal to or greater than” level of worker protection.
Alternative approaches to having a safeguard in place may involve combinations of the following:
- ensuring that a machine’s dangerous moving parts are out of the reach of workers i.e. safe by location or distance. For example, the machine can be located on the other side of a wall, or dangerous parts can be located high enough to be out of the normal reach of a worker. The main disadvantage of this approach is that if the equipment jams or becomes blocked, an operator might try to correct the problem with the machine turned on – and no safeguards in place. A worker can relatively easily gain access to the machine by using a ladder or stand on an object at hand to gain access to elevated dangerous parts. Safe by location or distance is an approach that is only suitable when policies and procedures are in place that ensure that the safety provided by this method is not compromised.
- marking danger zones that need to be kept clear of and ensuring that the zones are respected.
- restricting the number of machines that use an alternate guarding arrangement.
- “inching” or “inch-safe-service” procedures. These procedures involve limited motion of machinery where dangerous parts are exposed during cleaning, setting, adjustment or feeding material. The terms “jog”, “crawl” and “pulse” may also be used depending on the machine and industry. Machinery operated in this way normally has a “safe” or “hold-to-run” control, with the machine running at the slowest practical operating speed for the purposes of cleaning, loading and setting up. The inching control should be of a hold-to-run type so that on release of hand pressure the machine’s dangerous motion stops immediately.
- using procedures that are confirmed as offering an appropriate level of worker protection.
The employer is required to place signs in a clearly visible location(s) warning workers of automatically or remotely starting machinery. The signs may bear a message such as “WARNING – This Equipment May Start Without Warning”.