Category: Equipment

Some Common Safeguarding Applications

Power transmission guards:

Power transmission parts typically consist of belts, pulleys, chains, sprockets, gears, shafts, and couplings. Contact with these moving parts accounts for a large number of preventable injuries. It is usually a straightforward task to fabricate and install guards for these hazards.

Refer to “Design and performance requirements for barrier guards” (Part-1) for the do’s and don’ts associated with barrier guards. Two very common machine guards are:

V-belt/chain-sprocket guard

PTO (power take-off) drive shaft guard (frequently found in agriculture)

V-belt/chain-sprocket guard(Fig4.1)

Figure 4.1. Typical fabrication design of the V-belt/chain-sprocket guard.

PTO drive shaft guard

Unguarded PTO (power take-off) drive shafts account for a large number of serious entanglement injuries, especially in agriculture, where they are frequently used with tractors for powering portable machinery such as irrigation pumps. Because the equipment is powered for frequent, short periods there is a tendency to neglect installing guards over these drives. It is a good practice to install a chain or cable tether at each end of the PTO drive shaft guard so that the guard can be readily secured to the tractor or portable equipment when not in use.

Fig-4.2

Figure 4.2. PTO drive shaft guards. (A) With tether chain attached to each end of the guard. (B) Cutaway view of PTO drive shaft and typical guard.

Rotating shaft and coupling guard:

Fig-4.3

Figure 4.3. Typical design of a rotating shaft and coupling guard.

Conveyors

This section focuses on two common types of conveyors:

Belt conveyors
Screw (auger) conveyors

Belt conveyors

Injuries associated with unguarded belt conveyors generally involve one of two moving parts:

• The power transmission drive (V-belt or chain-sprocket drive and transmission)

• The conveyor belt itself where it engages around the head or tail spool (also known as the drum)

Guarding of the power transmission drive is done using the safeguarding methods described earlier for typical power transmission drives. Guarding of the in-running nip point between the running belt and the head or tail spool is achieved by fully enclosing access to the belt and spool for a minimum of 1 metre (3.3 feet) back from the centreline of the spool. In industry, this is often referred to as a “boot.” Figure 4.4B shows a typical belt conveyor tail spool boot. The boot must be designed and fabricated to permit tracking adjustments, which must be done when the belt is moving, to be performed without removing the boot.

Where access to the running conveyor belt is not prevented by guardrails or enclosure, a typical safeguarding device consists of an emergency trip wire running the entire length of the conveyor. This safety device must be installed using the safety criteria described under “Grab wire and pull wire devices” .

Figure 4.4. Typical belt conveyor boot guards. (A) Head spool guard. (B) Tail spool guard.

Screw (auger) conveyors

Screw conveyors are found in a wide variety of industrial operations,including ice houses, cement plants, pulp mills, grain and feed establishments, and farms. Injuries associated with unguarded screw (auger) conveyors are usually traumatic and extensive, and often result in fatalities from whole-body entrapment. Think of a screw conveyor as a large meat grinder. It is one of the least forgiving types of powered machinery. As with belt conveyors, there are two main sources of harmful engagement:

• The power transmission drive (V-belt or chain-sprocket drive and associated power reduction unit)

• The rotating auger (also known as the vane), which runs through a trough to move the material.

The power transmission drive is guarded using the methods described for typical power transmission drives (beginning on page). The auger itself is typically guarded using solid metal covers if no access to the trough is required during operation. When material must be fed into the running auger, such as those located at floor level in ice houses, guarding material such as grating or horizontal members are often used.
The following safety measures must be built into the guard design:

The openings in the guard are small enough to prevent a hand, arm, or foot from engaging the running auger (see “Power transmission guards and enclosures: maximum permissible openings”).

The guards are securely bolted in place using fasteners that require a tool for removal. Quick-release latches are not permitted.

Figure 4.5 shows a point-of-operation feed guard for an ice auger located at floor level. Because a worker is present at all times to tend the operation to ensure a flow of ice in the conveyor, the guards may be designed to allow ice to be shoveled onto the conveyor but must prevent any part of the worker’s body from touching the moving auger.

Figure 4.5. Ice auger conveyor with good functional design.located at floor level. Because a worker is present at all times to tend the operation to ensure a flow of ice in the conveyor, the guards may be designed to allow ice to be shoveled onto the conveyor but must prevent any part of the worker’s body from touching the moving auger.

Figure 4.5. Ice auger conveyor with good functional design.

Safe work practices for conveyors:

1. Don’t perform service on a conveyor until the motor disconnect is locked out.
2. Service a conveyor with authorized maintenance personnel only.
3. Keep clothing, fingers, hair, and other parts of the body away from the conveyor.
4. Don’t climb, step, sit, or ride on the conveyor at any time.
5. Don’t load the conveyor outside of the design limits.
6. Don’t remove or alter conveyor guards or safety devices.
7. Know the location and function of all stop/start controls.
8. Keep all stop/start control devices free of obstructions.

9. All personnel must be clear of the conveyor before the conveyor isstarted.
10. Operate the conveyor with trained personnel only.
11. Keep the area around conveyors clear of obstructions.
12. Report all unsafe practices to your supervisor.

Accidents around conveyors occur most frequently due to:

• Unguarded power transmission parts

• Unguarded nip points

• Unguarded shear points

• Unguarded pinch points

• Unguarded spill points

• Un barricaded access to areas under counterweights

• Tension take-up points

• Transfer mechanisms

• Absence of safe passage under conveyors

Feed rolls

Safeguarding feed rolls in general

Feed rolls are found in a wide variety of industries, such as paper products manufacturing and sheet metal production. They present a high risk of serious injury because of their high speed of operation.

Once a worker is caught in a feed roll, the damage is done quickly, and stopping the equipment will not undo it.

In general, there are two types of feed rolls:

• Those that run material into a machine but do not have to be accessed by workers. These can usually be safeguarded by enclosure or location within the machine.

• Those that are hand-fed as part of the production process. These require closer attention to safeguarding.

Safeguarding design criteria for feed rolls fed by hand Figure 4.6 provides guidance for designing fixed barrier guards to prevent hands from accessing the nip points created by feed rolls.

Please refer to “Point-of-operation (feed) guards: maximum permissible openings” beginning on for the safe distances for guard placement and guard openings.

You can also use the following rule of thumb to determine the maximum safe opening in a feed guard located less than 305 mm (12 inches) from the danger zone:

• Maximum safe opening = 6 mm (¼ inch) + 8 of the distance from the guard to the point where the rolls are 9 mm (a inch) apart (the danger zone)

You may have to make a sketch to determine this distance.
Example

A guard is needed for an operator feeding sheet goods into feed rolls 152 mm (6 inches) in diameter and 9 mm (a inch) apart. The guard must be within 102 mm (4 inches) of the centreline of the rolls in order to accommodate the type of material being fed.
How large a feed opening can be allowed under the guard?
Solution
The feed rolls meet at 9 mm (a inch) apart. The distance from thedanger zone (in this case, the centreline of the rolls) to the guard is therefore 102 mm (4 inches). The maximum permitted opening is: 6 mm (¼ inch) + 8 of 102 mm (4 inches) = 6 mm (¼ inch) + 12 mm (½ inch) = 18 mm (¾ inch)

Metal-forming equipment

Punch presses

Types of punch presses A punch press is a machine used for piercing holes or other openings in sheet metal or plate. The tooling or die set consists of two parts: the upper male punch and the lower female die. The punch is fitted to a ram or slide, which moves down and up by mechanical, hydraulic, or pneumatic power. The punch pierces the material and enters the lower die. A punch press can be small and manually operated and hold one punch and die, or be very large and CNC (Computer Numerical Control)-operated, and hold many punches and dies of various sizes and shapes.

Punch presses are manufactured in many shapes and sizes, ranging from 2-ton benchtop models to 500-ton floor models and larger. The tonnage of a punch presses refers to the total force between the dies. In an oversimplified example, a 100-ton punch press with a 25.4 cm (10 inch) × 25.4 cm (10 inch) die area (645 cm2 [100 square inches]) will achieve a force of 13,800 kilopascals (1 ton per square inch).

A press that must complete one full revolution before the stroke can be stopped is called full revolution clutch. A press equipped with an air-friction clutch, and with a proper control package, is capable of being safely stopped anywhere during its stroke. This type of press is called part revolution clutch. The difference is important because it will dictate the types of safeguards that can be used.

Presses can be further classified by the type of power source:  mechanical (electrical motor and flywheel for energy transfer to the crankshaft) or hydraulic.

Figure 4.7 shows the two most common punch presses found in general use.

Figure 4.7. Most common punch presses in general use. (A) Straight side hydraulic power press (no flywheel) – press remains in vertical position. (B) OBI (open back inclinable) mechanical punch press – press can be tilted back to allow formed parts to drop out of the back.

Methods of safeguarding

The two critical areas of safety on punch presses are:

• Point-of-operation (feed point) safeguarding

• Control reliability (can the machine come to a safe stop consistently and reliably in the event of an unsafe condition or when an emergency stop signal is given?)

Because a punch press can be used for many different operations (hand feeding, automatic strip/coil feeding, and so on) there are several effective ways to safeguard the point of operation. Figure 4.8 shows the many options available.

Figure 4.8. Safeguarding options for punch and brake presses.

Brake presses

Types of brake presses

Whereas punch presses are generally used for piercing metal, brake presses are used mostly for bending sheet or plate metal. Brake presses are generally rated by the length of the press bed. The longer the bend, the longer the piece that can be inserted into the dies. Each cycle of a brake press is called a stroke.

Brake presses are normally fed by hand and operated with a foot control, which places them at high risk for amputations. Brake presses have part revolution clutch operation; if the foot treadle or electrical control is released, the ram (the part that holds the upper die and moves down and up) either stops or returns to top of stroke.

Brake presses are also classified by the type of power source:

• Mechanical (electrical motor and flywheel for energy transfer to the crankshaft)

• Hydraulic

• Hydro-mechanical (a combination of mechanical actuation with hydraulic assist)

Methods of safeguarding:

The two critical areas of safety on brake presses are:

• Point-of-operation (feed point) safeguarding

• Control reliability (can the machine come to a safe stop consistently and reliably in the event of an unsafe condition or when an emergency stop signal is given?)

The options for safeguarding the point of operation of a brake press are somewhat limited. This is because the profile of the formed piece is substantially different after the bending process. What goes into a narrow die space as flat stock may have to be removed as a complex shape, so brake press operations generally require a fair amount of open space between the dies. The exception to this would be smallpiece parts that can be fed into an open die space of 6 mm (¼ inch) or less (safeguarded by minimum opening) and removed without difficulty. Additional safeguarding is required at the ends of the press.

Besides point-of-operation safeguarding, an awareness barrier, usually in the form of a chain or rope with appropriate signage, should be installed across the back of the brake press to deter access by unqualified persons.

Point-of-operation safeguarding is generally limited to three options:

• Light curtain devices that are mounted at either end of the press bed and detect entry of a hand or body part into the die space. These devices can be programmed to recognize the varying profiles of piece parts and selectively mute or blank out the light beam channel(s) that may interfere with the proper functioning of the light curtain. These devices offer the least interference with normal press operation. They are particularly well suited to hydraulic brake presses. If they are retro-installed on a mechanical brake press, modifications will have to be made to the existing brake and clutch system, and a control-reliable package will have to be installed.

• Two-hand controls coupled with foot switch operation. This type of conversion package uses control-reliable components to enable the operator to bring the ram down to a 6 mm (¼ inch) or less closure using two-hand controls, then change over to foot control operation. The foot control is inoperative during the initial part of the downstroke. This method normally requires the piece part to be supported for productive operation.

• Pull-back or restraint devices. Although not commonly used, they might be considered for some dedicated brake press operations with infrequent die and piece part changes.

Power shears (sheet metal and plate):

The two critical points of operation on a guillotine shear are:

• The blade, which does the actual cutting

• The hold-down clamps or “feet,” which hold the work piece in position during the cutting cycle

The hazards posed by the blade and clamps are hidden by the guard (Figure 4.9).

Methods of safeguarding:

Three type of safeguards are used to protect the point of operation of shears:

• A fixed barrier guard designed with openings large enough to allow the flat stock into the shear but small enough to keep fingers out.

• A fixed barrier guard with an awareness modification that allows larger thicknesses of plate steel (greater than 12 mm [½ inch]) to enter the shear but warns the operator that his or her fingers are approaching the danger area.

• Two-hand controls, which are not common but are found in some specialized cut-to-length operations

Besides point-of-operation safeguarding, an awareness barrier, usually in the form of a chain or rope with appropriate signage, should be installed across the back of the shear to deter access by unqualified persons.

Hand-fed powered metal-forming rolls:

Steel fabrication shops make use of equipment for rolling sheet metal or plate into cylinders. These metal-forming machines are often referred to as “pyramid rolls” or “initial pinch offset rolls” (Figure 4.10). They present a unique safeguarding challenge: the point of operation must remain accessible during the entire forming operation. This exposes both the operator and helper to the risk of being drawn into the powered rolls. Safeguarding usually consists of an emergency body contact device such as cable wire or a bumper bar (see “Miscellaneous emergency body contact devices” on page 40) that will be involuntarily activated by the operator or helper in case of entrapment in the rollers.
Because the rolls are under very high operating pressure, the equipment will normally come to a very sudden stop when the emergency stop device is activated. It is important that this device be installed so that both the operator and the helper can access it.

Abrasive equipment:

An abrasive tool uses an abrasive wheel to wear away the surface of a workpiece to change its shape.  An abrasive wheel consists of a bonded abrasive material with properties specific to the material being worked; for example,  a wheel intended for ferrous material may not be suitable for grinding nonferrous material.

There are three common types of grinding machines:

• bench grinders,

• pedestal grinders, and

• portable grinders.

The greatest risk associated with abrasive equipment is fragmentation of an abrasive wheel. The size and peripheral speed of the wheel determine the amount of energy that will be released in the event of a failure. The main objective of safeguarding is to contain pieces of the abrasive wheel if a rupture occurs.
There are two important areas where training and safeguarding will prevent serious injury and death:

• Proper storage and handling of abrasive wheels

• Appropriate safeguarding of stationary and portable grinders

Proper storage and handling of abrasive wheels Wheels (especially vitrified or glass-based wheels) are easily damaged if they are bumped or dropped. That is why it is so important to store and handle them carefully.

• Check all wheels when you receive them and before using them.

• Follow the manufacturer’s instructions for storage. Proper sorting and storage of grinding wheels will help ensure easy access, less handling, and less chance of error.

• Store grinding wheels in an area that is dry and protected against damage from impact, solvents,high humidity, and extreme heat or cold.

• Store portable grinders on hooks or in V-shaped racks. Protect racks from damage.

• Arrange grinding wheels so that older ones will be chosen before newer ones.

• Never roll a wheel on its edge; it may absorb oil or dirt from the floor, and get damaged.

Design criteria for abrasive wheel guards:

Figure 4.11 illustrates the maximum wheel exposures for guards on two types of abrasive equipment: bench and pedestal grinders (90° exposure) and hand-held angle grinders (180° exposure). When a portable grinder is being used for grinding root passes in welded pipe, the protective hood must cover at least 120° of the wheel periphery and the operator must wear adequate eye and face protection.

Figure 4.11. Maximum wheel exposures for different types of abrasive wheel guards.

Safe work procedures for bench and pedestal grinders:

• Pedestal grinders must be securely attached to the floor. Benchgrinders should be securely fastened to a bench.

• Always check that the rated RPM (revolutions per minute) of the grinding wheel is consistent with the rotational speed of the grinding machine.

• Always wear eye protection (safety glasses or impact-rated face shield).

• Never remove wheel guards from a bench/pedestal grinder. They offer protection in case of wheel failure, and protect hands and fingers from injury.

• Work rests or tools rests must be provided on all machines. The work rest must be securely fixed and adjusted close to the grinding wheel (maximum distance of 3 mm [8 inch]). It should be adjusted as the disc becomes smaller through wear and dressing. Never adjust tool rests while the grinder is running.

• Before commencing grinding, allow the grinding wheel to run at operating speed for at least one minute. Do not stand directly in front of a grinding wheel when it is first started. Do not use a wheel that vibrates.

Woodworking equipment:

Equipment and machinery used in woodworking are dangerous when used improperly or without proper safeguards. The most common injuries to workers are lacerations, amputations of the fingers and hands, and loss of sight. Besides traumatic injuries, workers in this industry can suffer from skin and respiratory diseases from exposure to wood dust and the chemicals used in finishing.

This section describes the principal hazards of woodworking equipment and some methods for controlling these hazards through safeguarding. It is not a substitute for a thorough knowledge of the Occupational Health and Safety Regulation. This section does not cover machinery used in the primary production of lumber and basic wood materials at sawmills and lumber remanufacturing plants.

Safety and health hazards:

The main occupational hazards associated with woodworking operations are as follows.

Safety hazards:

• Machine hazards (point of operation, power transmission components)
• Kickbacks
• Flying chips and material
• Tool projectiles (unbalanced cutter heads)
• Fire and explosion
• Electrical

Health hazards

• Chemical (sensitization from exposure to finishes, coatings,
• adhesives, solvents)
• Wood dust (some are carcinogens)
• Noise
• Vibration

Safeguarding commonly used on woodworking machines:

The following are recommended point-of-operation safeguarding techniques and safe work practices for several machines commonly used in the woodworking industry. Personal protective equipment is not specifically covered because its use applies to all industrial machinery. Work practices that apply to all woodworking equipment (such as using a brush for cleaning saws) are not covered either.

Figure 4.12. Typical table saw.

Radial arm saw

Figure 4.13. Typical radial arm saw.

Use and operation:

Radial arm saws are circular saws that rotate downward either with (rip) or against (crosscut) the wood grain. For crosscutting, the wood is placed against a fence away from the operator and the blade is pulled into the stock. For rip cuts, the blade is set parallel to the fence and the
stock is pushed through.

Radial arm saws have features that make them more versatile than table saws. The saw arm can be raised and lowered and swung to the side to adjust the depth and horizontal angle of the cut. The blade can be replaced with shaping cutters, disk or drum sanders, or other  accessories.

Recommended safe work practices:

• During crosscutting, operate the saw on the side of the table with the handle.

• During ripping, make sure the stock is fed in the correct direction to avoid serious kickback hazard.

• Clearly mark the direction of saw rotation on the protective hood (guard).
• Measure boards using an end stop gauge. If measuring by rule, turn off the saw. Wait for the blade to stop before making measurements.
• Before performing angular cuts, check the intended direction of the saw blade (for example, compound 45° cuts).

Band saw:

Figure 4.14. Typical band saw.

Use and operation:

Band saws are used both for straight sawing and for cutting curved pieces. The band saw uses a thin, flexible, continuous steel strip with cutting teeth on one edge. The blade runs on two pulleys, one driven and the other an idler, through a hole in the work table on which stock is fed. The operator hand-feeds and manipulates the stock against the blade to saw along a predetermined line.

Recommended engineering controls

• Guard the blade entirely except at the point of operation (the working portion of the blade between the bottom of the guide rolls and the table).

• Use a self-adjusting guard for the portion of the blade between the sliding guide and the upper saw so that it rises and lowers with the guide.

• Properly adjust the blade guide post to fit the thickness of the stock and to provide additional guarding.

• Fully enclose the band wheels.

• Guard feed rolls if they are used as a method of feeding the saw.

• Consider installing a braking system on one or both wheels to minimize the potential for coasting after the saw has been shut off; otherwise, do not remove material until the blade has stopped.

• Make sure the saw includes a tension control device to indicate proper blade tension.

Industrial robots and robotic systems:

The use of robots and robotic systems in manufacturing has become mainstream in large manufacturing operations such as the automotive industry, and their use in small manufacturing plants and niche operations will increase. Unauthorized entry into the working envelope of a robot exposes a worker to the potential for serious impact or crushing injuries from the unexpected movement of the robot. The safeguarding of robots requires a systems approach to safeguarding. It typically uses a combination of fixed barrier fences, interlocked gates, and presence-sensing devices such as safety mats and light curtain devices. Figure 4.17 shows a typical robot work cell safeguarding system.

Figure 4.17. Typical robot work cell safeguarding system.

Signage : Machine operations

click the below link to download machine and equipment signage, tool box talk

Equipment – Tool box talk

Introduction

It is crucial to understand why machine and equipment safe guards are to be used on machines. An operator or maintenance worker must be informed as to the location of the safe guards on the machines, and should also be provided information on why safe guards protect them and what hazards they protect them from.

An operator or maintenance worker also should be trained on how to remove machine and equipment safe guards from the machines and also to understand in what circumstances guards can be removed. Workers need to be trained in procedures to follow if they notice guards are damaged, missing or inadequate.

An operator or maintenance worker should be provided with a dress code. For example; no loose fitting clothing or jewelry. These items could easily be caught in the equipment or  machines. From the simplest hand tool to the most complex machinery… operational safety hazards exist with any equipment.

The Machine Guard Program is designed to protect Employees from hazards of moving machinery. All hazardous areas of a machine shall be guarded to prevent accidental “caught in” situations. References: General Requirements for all

• Machines (29 CFR 1910.212),

• Woodworking Machinery (29 CFR 1910.213),

• Abrasive Wheels (29 CFR 1910.215),

• Power Presses (29 CFR 1910.217),

• Power Transmission (29 CFR 1910.219).

Machine & Equipment Hazards:

Electrical Hazards – equipment that uses electricity as a power source is a potential electrocution hazard. Check power cords, switches and connections for exposed wires or broken parts.

Amputation & Caught-in Hazards – machine guards on equipment are installed to protect our employees from moving parts.   Of course if they have been removed during maintenance or adjustment they will no longer provide protection.  Check equipment every day to ensure that all guards are in place.

Chemical Hazards –  processing equipment that uses chemicals can be sources of numerous hazards.  Leaks can cause slip hazards as well as possible exposure to harmful chemicals.  Hoses that leak could create a respiratory problem from vapors.

Sharp Edges –   simply walking past machinery may be hazardous if sharp edges are not guarded  check equipment mounting brackets, sign edges and control boxes to see if sharp edges are present.

Eye Hazards – tools and equipment that create chips, sparks or dust are potential eye hazards.  These types of eye hazards are generally controlled by safety glasses, goggles and face shields.   Check eye protection your workers use to make sure they are not broken, scratched and are the correct type for the hazard.  As a minimum, anyone who uses hand or power tools should wear safety glasses.

PPE –   personal protective equipment should be considered a secondary line of defense against equipment hazards.  Employees need to know how to properly select, use and clean any PPE they use.  PPE does wear out and has limitation on the level of protection against hazards – your workers should know these limitations.

Definition of Terms:

1. Guards: Barriers that prevent Employees from contact with moving portions or parts of exposed machinery or equipment which could cause physical harm to the Employees.

2. Enclosures: Mounted physical barriers which prevent access to moving parts of machinery or equipment.

3. Point-of-Operation: The area on a machine or item of equipment, where work is being done and material is positioned for processing or change by the machine.

4. Power Transmission: Any mechanical parts which transmit energy and motion from a power source to the point-of-operation. Example: Gear and chain drives, cams, shafts, belt and pulley drives and rods. NOTE: Components which are (7) feet or less from the floor or working platform shall be guarded.

5. Nip Points: In-Running Machine or equipment parts, which rotate towards each other, or where one part rotates toward a stationery object.

6. Shear points: The reciprocal (back and forth) movement of a mechanical part past a fixed point on a machine.

7. Rotating Motions an exposed mechanism are dangerous unless guarded. Even a smooth, slowly rotating shaft or coupling can grasp clothing or hair upon contact with the skin and force an arm or hand into a dangerous position. Affixed or hinged guard enclosure protects against this exposure.

8. Reciprocating: Reciprocating motions are produced by the back and fourth movements of certain machine or equipment parts. This motion is hazardous, when exposed, offering pinch or shear points to an Employee. A fixed enclosure such as a barrier guard is an effective method against this exposure.

9. Transverse Motions: Transverse motions are hazardous due to straight line action and in-running nip points. Pinch and shear points also are created with exposed machinery and equipment parts operating between a fixed or other moving object. A fixed or hinged guard enclosure provides protection against this exposure.

10. Cutting Actions: Cutting action results when rotating, reciprocating, or transverse motion is imparted to a tool so that material being removed is in the form of chips. Exposed points of operation must be guarded to protect the operator from contact with cutting hazards, being caught between the operating parts and from flying particles and sparks.

11. Shearing Action: The danger of this type of action lies at the point of operation where materials are actually inserted, maintained and withdrawn. Guarding is accomplished through fixed barriers, interlocks, remote control placement (2 hand controls), feeding or ejection.

Hazards:

Use of machinery or equipment with inadequate guards or damaged controls can result in:

• Amputation

• Skin Burns

• Cuts & fractures

• Death

Hazard Controls:

controls used to prevent exposure to moving or energized machine parts includes:

• Machine guards

• Interlocks

• Presence sensing devices

• Gates

• Two-hand controls

• Employee training

Machine Guarding Requirements:

1. Guards shall be affixed to the machine where possible and secured.

2. A guard shall not offer an accident hazard in itself.

3. The point-of-operation of machines whose operation exposes an Employee to injury shall be guarded.

4. Revolving drums, barrels and containers shall be guarded by an enclosure which is interlocked with the drive mechanism.

5. When periphery of fan blades are less than 7 feet above the floor or working level the blades shall be.

Machinery and equipment hazards:

Hazards created by machinery and equipment can be classified as mechanical and non-mechanical.

Mechanical hazards

Recognizing mechanical hazards

A good way to recognize mechanical hazards is to observe how the moving parts of a machine operate and how parts of a worker’s body are likely to come into harmful contact with them.

Machine parts generally move in one of three ways: they rotate, they slide, or they can rupture, fragment, and/or eject.

• Single rotating parts, such as shafts or couplings, present a risk of snagging or entanglement. Two or more parts rotating together, such as feed rolls and V-belt and pulley drives, create nip points(see Figures 1.1 and 1.2).

• Parts that slide or reciprocate, such as dies in punch presses, create shearing or crushing hazards.

• Parts that can rupture or fragment, such as an abrasive wheel, may cause impact injuries.

Figures 1.1 to 1.5 illustrate common mechanical hazards where hands, limbs, hair, clothing, and sometimes the entire body can be injured from harmful contact with unguarded moving machine parts. The illustrations show typical cases, not all possibilities.

Principal mechanical components of machinery .Most machines have three principal components:

• A power source (often an electrical motor)

• A power train that transfers moving energy

• Tooling

Hazards from these components generally involve the following:

• Power transmission parts. These are the moving parts of the power train. They usually consist of belts, pulleys, chains, sprockets, gears, shafts, and couplings. Many of the moving parts illustrated in Figures 1.1 and 1.2 are power transmission parts.

• Point of operation. This is where the tooling of the machine is contained and the machine’s work is performed. The term “feed point”is sometimes used to describe the working area of the machine.

The types of machine components and drives shown in Figures 1.1 to 1.5 are very common in most industrial operations. They account for a large number of serious injuries in the workplace.

Figure 1.1. Single rotating parts presenting a snagging/entanglement hazard.

(A) Snagging hazard from projecting flange bolts on rotating coupling.
(B) Snagging hazard from projecting key way and set screw on rotating shaft.

Figure 1.2. Multiple rotating parts presenting an in-running nip point hazard.

(A) V-belt and pulley drive: a common source of in-running nip points on powered industrial machinery. (B) Typical chain-sprocket drive. (C) Typical exposed gears. (D) Typical feed rolls.

Figure 1.3. Combination of rotating and sliding parts and reversing parts, creating two
in-running nip point hazards.

(A) Rack and pinion gears. (B) Conveyor belt spool.

Figure 1.4. Sliding/pivoting movement creating struck by/crushing hazards.

(A) Sliding milling table striking worker in abdomen.
(B) Sliding milling table crushing worker against adjacent wall.(C) Worker struck by robot arm.
(D) Scissor lift creating crushing/shearing hazards

Figure 1.5. Hazards from fragments and projectiles.

(A) Fragments from exploding abrasive wheel. (B) Projectile from pneumatic nail gun.

Health hazards:

Workers operating and maintaining machinery can suffer adverse effects other than physical injury caused by moving parts. They can be exposed to hazards through inhalation, ingestion, skin contact, or absorption through skin. For example, without adequate safeguards, control measures, and personal protective equipment, a worker may be at risk of occupational disease resulting from exposure to:

• Toxic or corrosive chemicals that can irritate, burn, or pass through the skin

• Harmful airborne substances that can be inhaled, such as oil mist, metal fumes, solvents, and dust

• Heat, noise, and vibration

• Ionizing radiation such as X-rays and gamma rays

• Non-ionizing radiation such as ultraviolet light (UV), radio frequency (RF) energy, and lasers

• Biological contamination and waste

• Soft tissue injuries (for example, to the hands, arms, shoulders, back, or neck) resulting from repetitive motion, awkward posture, extended lifting, and pressure grip

Other hazards

• Some hazards are associated with things other than moving parts:
  1. Slips and falls from and around machinery during maintenance
  2. Unstable equipment that is not secured against falling over
  3. Fire or explosion
  4. Pressure injection injuries from the release of fluids and gases under high pressure
  5. Electrocution from faulty or ungrounded electrical components

What is a safeguard:

A safeguard is a solution or a combination of solutions that eliminate or reduce the risk of exposure to hazardous moving parts or other harmful conditions. Safeguards range from fixed barrier guards (most effective) and safeguarding devices to safe work procedures and personal protective equipment (least effective) (see the hierarchy of safeguarding solutions on below). A comprehensive risk assessment will determine which safeguards are most effective.

Hierarchy of safeguarding controls:

When selecting a safeguard or a combination of safeguards, always start at the top of the hierarchy shown below. Choose a less effective safeguard only when the more effective solution is impracticable. For example, you may be able to eliminate the need to hand-feed a machine by installing an automated feeder. Installing a fixed barrier guard across a feed point may be practicable if the feed stock is a flat sheet metal blank; for larger material, you may have to allow access
to the point of operation using two-hand controls or a light curtain (a presence-sensing device) instead.

Classification of safeguards:

There are six general ways to safeguard machinery and equipment:

• Barrier guard

• Safeguarding devices

• Location

• Awareness means

• Training and procedures

• Personal protective equipment

Barrier guards:

Properly designed and installed barrier guards provide the most effective protection to workers. Fixed barrier guards are the first choice of engineering control to keep workers from contacting hazardous moving parts or to contain harmful fluids and projectiles, particularly when access is not normally required during operation. Fixed barrier guards must be secured with at least one fastener requiring a tool for removal.

When a barrier guard must be moved aside to enable a worker to access a point of operation or feed point during normal production work, the guard must be interlocked to disable the control system until the guard is put back in place and the control system is reset. Some barrier guards are adjustable to allow materials of varying thickness to be fed into a machine. Some guards are attached to the tooling or dies that fit into a machine. These are a special type of barrier guard called die enclosure guards.

A common requirement of all barrier guards is that they prevent a worker from reaching around, over, under, or through the guard to the danger area.

Safeguarding devices:

Access to feed points and ejection of formed parts is often required during normal machine operation. This may make the use of a fixed barrier guard, or even an interlocked guard, impracticable. Fortunately there are a number of safeguarding devices that can provide a high
level of protection to workers.

These devices generally operate in one or a combination of ways:

• Requiring the operator to remove his or her hands or entire body from the danger area before the machine can be cycled. Two-hand controls and interlocked gate guards function this way.

• Stopping the machine if the operator or another worker enters the danger area while the machine is cycling. Presence-sensing devices such as light curtains and photoelectric devices and pressure sensitive mats function this way. These devices depend for their effectiveness on a very reliable braking system and associated control system.

• Physically restraining the operator from reaching into the danger area of the machine at any time. This can be done through the use of a restraint device such as a safety belt and lanyard.

• Involuntary tripping or activation of an emergency stop device if all or part of a worker’s body approaches or enters the danger area. Examples include a “crash bar” or “belly bar” in front of a trim.saw in-feed lug chain; the emergency contact bar in front of the in running feed rolls of a flat work ironer; and the emergency trip wire installed along a conveyor system.

• Limiting machine movement or travel to a safe range or speed. Examples include operating the machine in a “jog,” “inch,” or “setup” mode, activated by special control buttons (printing presses); limiting die movement to 6 mm (¼ inch) or less before a piece can be inserted into the dies; an anti-repeat device that prevents a machine from performing more than one cycle (single stroke mode).

• Locating the worker in a safe place before the machine can be started. Examples include a foot control fastened to the floor a safe distance from the machine (called “captive” or “hostage” control); the activating control for an X-ray machine located in an isolated room.

• “Hold-to-run controls,” which require the operator to keep the control activated in order for the machine to continue to operate (also known as “dead man” or “operator-maintained” controls).

• “Captive key systems,” which use a series of keys and locks to start or shut down a hazardous operation in a prescribed and safe sequence.

Safeguarded by location:

Machinery may be safeguarded by location if the distance to dangerous moving parts is greater than 2.4 meters (8 feet) from any floor, walkway, access platform, or service ladder. Any work on the machine must be performed using lockout.

Warning devices:

Some machine hazards cannot be practicably safeguarded using the methods described above. In these cases, less effective means may have to be used to minimize or reduce the danger to workers. These may include such devices as splash shields; flashing lights, strobes, and beacons; audible warning devices such as beepers, horns, and sirens; warning signs, decals, and barrier chains and ropes to restrict access. You will need to consider the work environment and layout to determine whether these measures will be effective.

Training, supervision, and procedures:

Also known as administrative controls, training, supervision, and procedures are near the low end of the hierarchy of protection because their effectiveness depends on human factors such as adequate training and supervision. Lockout is an example of such a procedure.

Personal protective equipment:

Personal protective equipment may have to be used even when other machine hazards are effectively safeguarded. In some cases, such as operating a powered forging hammer, the only protection available to the operator, besides training and safe work procedures, may be eye and face protection, hearing protection, and hand protection.

Barrier guards:

Typical barrier guards

Figures 3.1 to 3.3 show examples of typical barrier guards.

Figure 3.1. Fixed power transmission guard.

Figure 3.2. Adjustable guards.(A) Adjustable band saw guard. (B) Adjustable power press feed guard.

Figure 3.3. Handheld circular saw guard, an example of a self-adjusting (self-retracting) guard. Guardsdesigned for right-handed people can sometimes cause problems for those who are left handed. A lefthandedperson often has difficulty operating a handheld circular saw.

Design and performance requirements for barrier guards:

Barrier guards are the preferred means of safeguarding when access is not required during normal operation.

Fixed barrier guards must:

• Prevent access to the danger area from all directions
  (AUTO: around, under, through, over)

• Not create additional pinch points or other hazards .

• Safely contain broken parts (such as belts and chains).

• Be secured by at least one fastener requiring a tool for removal,unless properly interlocked with the machine control system.

• Allow for safe lubrication and minor adjustments.

Fixed barrier guards should:

• Offer good visibility to feed points.

• Stand up to normal wear and tear.

• Meet normal production and quality needs.

• Be difficult to modify or defeat.

Point-of-operation (feed) guards: maximum permissible openings:

Point-of-operation guards (also known as feed guards) are often designed with horizontal members to enable the operator to insert flat stock into the machine. Figure 3.5 shows how the openings between the horizontal guarding members decrease as the worker’s fingers come closer to the pinch point.

Hand-feeding equipment usually presents the highest risk of injury to a worker. Feed guards must be carefully designed to ensure that theworker’s hands cannot access the danger point. Table 3.1 and Figure 3.5give the necessary clearances for an effective point-of-operation guard with a horizontal slotted feed opening.

Table 3.1. Maximum permissible openings in point-of-operation guards based on distance to hazard.

Figure 3.5. Visual representation of Table 3.1.

Safeguarding devices

Typical safeguarding devices:

Figures 3.7 to 3.12 show examples of typical safeguarding devices.

Figure 3.7. Two-hand controls.

(A) Two-hand controls – power press. The press will not cycle unless bothrun buttons are activated using both hands within a certain time period of each other.

(B)Two-handcontrol levers – paper guillotine shear. The shear will not cycle unless both levers are activated, whichrequires the use of both hands within a certain time period of each other.

Figure 3.8. Light curtain or similar photoelectric sensing device.

(A) Light curtain – brake press.The press is operated in the normal manner using the foot control. It will stop if hands enter the light beam-protected zone.

(B) Light curtain – access to robotic cell. The robot is deactivated if a person enters the doorway protected by a light curtain safeguarding device.

Figure 3.9. Interlocked guard. The interlocked door must be closed before the machine can be started.

Figure 3.10. Pullback and restraint devices (not in common use).

(A) Press operator using pullback devices.The operator’s hands are pulled away by cables if the operator leaves them in the danger area.

(B) Brake press operator using fixed restraint devices. The operator’s hands cannot reach the danger area; hand tools would be required for access.

Figure 3.11. Emergency contact or tripping device in the form of an emergency “belly bar” on a calender.

The operator cannot reach into the in-running feed rolls without automatically activating the machine’s emergency stop bar.

Figure 3.12. Pressure-sensitive safety mat safeguarding access to machine.

The machine will come to an emergency stop if anyone, including the operator, steps on the mat.

Design and performance requirements for presence-sensing devices:

How it is work:

Unlike barrier guards and two-hand controls, presence-sensing devices do not prevent access to a hazardous point of operation. However, they prevent dangerous machine motion if any part of a worker’s body is in the danger area when a machine cycle is initiated. They are a good choice of safeguard when frequent access is required for loading parts and making adjustments during normal operation and physical guarding is too restrictive. These safety devices prevent dangerous motion while permitting unrestricted access by sensing the presence of the operator and sending a stop signal. Examples include light curtains, proximity sensors, and safety mats.

There are many technical factors, such as machine control reliability and safety distance, that affect the proper selection and positioning of light curtains, proximity sensors, and safety mats. Refer to the following:

standards referred to in the Occupational Health and Safety Regulation:

• CSA Standard Z432, Safeguarding of Machinery.

• CSA Standard Z142, Code for Punch and Brake Press Operation: Health,Safety and Guarding Requirements.

• CSA Standard Z434, Industrial Robots and Robot Systems – General Safety Requirements

Photoelectric light curtains:

These devices emit a “curtain” of harmless infrared light beams in front of the hazardous area. When any of the beams is blocked, the light curtain control circuit sends a stop signal to the machine’s control system. This type of safeguard offers the maximum protection with the minimum impact on normal machine operation. It is particularly well suited to safeguarding brake press operations. Note: steam or dust can inadvertently affect a light curtain.

Pressure-sensitive safety mats:

These devices are used to guard the floor area around a machine. A matrix of interconnected mats is laid around the hazard area, and the proper amount of pressure (such as an operator’s footstep) will cause the mat control unit to send a stop signal to the guarded machine. Pressure sensitive mats are often used within an enclosed area containing several machines, such as flexible manufacturing or robotics cells. When access into the cell is required (for example, in the case of robot “teaching”), the mats prevent dangerous motion if the operator strays from the safe area.

Design and performance requirements for safety interlocks

Horizontal injection molding machine with interlocked gate guard

How it is work:

If access to a point of operation (a feed point) is required during normal operation, a movable open able barrier guard interlocked with the machine’s power source can be a reliable and cost-effective solution. The control power for the machine is routed through the safety contact of the interlock. The interlock ensures that the machine will not operate if the guard is in the open position. The power source for the machine is usually electrical, but it could also be pneumatic or hydraulic.

If the interlocked guard can be opened during operation, the machine will stop. This is called simple interlocking. Some interlock switches also have a locking device that locks the guard door closed and will not release it until the machine comes to a safe stop. The feature is found in some households’ spin cycle washing machine. It is referred to as power interlocking. It is used with machinery such as tumblers and centrifuges, where the coasting down time may take several seconds to several minutes.

Movable gate:

A unique safeguarding application using interlocking is the movable gate device. It is commonly used to provide protection to an operator when hand-feeding parts into a punch press, but it can be applied tovarious other machines. See Figure 3.13.

Figure 3.13. Movable interlocked gate mounted on a punch press.

When the machine completes its cycle or returns to top of stroke (in the case of a power press), the gate automatically opens, allowing the operator to remove the formed part. The operator then places a feed stock (blank) into the machine and activates the controls to start another cycle. This can be done with either a foot control, a single hand control, or even two-hand controls (preferred). The gate must close before the machine can cycle. A low-pressure air cylinder attached to the gate performs this closing function. If there are any obstructions under the gate (such as the operator’s hands), the gate will not fully close. The interlock switch will prevent further machine operation until the obstruction has been removed and the controls reset.

Shields and awareness barriers:

How it is work

Shields, usually in the form of transparent barriers, are typically installed on lathes, milling machines, boring machines, and drill presses. They can also be used on woodworking machines. They are generally intended to deflect chips, sparks, sward, coolant, or lubricant away from the operator and other workers in the machine area. Besides providing some protection as a barrier, most shields also provide good visibility into the point of operation.

Awareness barriers include installations such as electrically interlocked pull cable assemblies installed in the rear area of machines such as brake presses and shears to restrict worker entry. These areas are often out of the operator’s view. The machine is stopped if someone pulls or loosens the cable. It is recommended that a sign denoting the danger be placed on the pull cable.

Although shields and awareness barriers offer some degree of safeguarding, they cannot be considered guards because they only restrict but do not prevent access to the danger area.

When installing these devices and before moving them from their normally applied position, always turn off power to the machine; follow lockout procedures if there is a risk of accidental startup.

Safeguarding by location:

With the body upright and standing at full height, the safe clearance when reaching upward to an unguarded hazard is a minimum of 2.5 metres (8 feet) (see Figure 3.16). Any hazardous moving parts beyond this distance are considered to be guarded by location. If access to hazardous locations is gained by use of ladders, scaffolds, and so on, temporary guarding or lockout procedures must be used.

Guide to selecting the right safeguard:

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