How To Use a Guard Opening Scale

Point-of-operation barrier guards are essential safeguarding equipment for hazardous industrial processes and machinery such as presses, pumps, motors and drills. When properly installed the barriers prevent a person from placing any part of their body into the point of operation by reaching through, over, under or around the guards to access a hazard. However, because barrier guards are typically constructed out of materials such as wire mesh, expanded metal, rods, or hairpins, most have openings that present the potential for injuries if a person reached through them. As a result, whether the guard is fixed, adjustable, movable, or interlocked, any openings must be measured for compliance with Table O-10 of OSHA 29 CFR 1910.217 (Mechanical Power Presses), current ANSI/CSA standards, or International standard ISO 13857 to determine the safe distance from the hazard.

The critical role of measuring barrier openings falls on a simple but often misunderstood tool: the Guard Opening Scale. Also known as “gotcha sticks,” Guard Opening Scales mimic the human hand and forearm. Over the past 70 years they’ve proven to be the most accurate means of ensuring any opening in a barrier guard will not allow a hazardous zone to be accessed.

HISTORY OF THE GUARD OPENING SCALE
The history of the Guard Opening Scale dates back to 1948. It was then that Liberty Mutual Insurance, joined with the Writing Committee for the ANSI B11.1 Safety Standard on Mechanical Power Presses, engineered a stair-step shaped measurement tool to determine guard-opening size vs. guard distance to the nearest Point of Operation hazard. A rash of injuries to mechanical power press operators who reached through barriers and suffered lacerations, amputations and crushed limbs prompted Liberty Mutual’s actions. Although Guard Opening Scales were first designed for point of operation guards on mechanical power presses, they are now often used on other machines as well.

Originally, the recommended dimensions used for the scale were based upon “average-size hands,” which at the time were a woman’s size 6 glove. ANSI incorporated these dimensions from Liberty Mutual into its 1971 revision of the ANSI B11.1 safety standard for mechanical power presses. In 1995, however, a study entitled “A Review of Machine-Guarding Recommendations” was conducted by Donald Vaillancourt and Stover Snook of Liberty Mutual Research to establish whether the 1948 drawings were consistent with current hand size data, in particular as the data relates to women and minorities who have become more prevalent in manufacturing. Vaillancourt and Snook suggested several important modifications including moving the glove size from a woman’s size 6 to a size 4. Drawings from the study have been adopted in several current ANSI B11-series safety standards for machine tools as well as in the ANSI/RIA R15.06 safety standard for industrial robots and robot systems. OSHA in Table O-10 of OSHA 29 CFR 1910.217 did not, on the other hand, officially adopt the drawings.

OSHA VS. ANSI GUARD OPENING SCALES
OSHA Compliance Officers are usually limited to using OSHA’s own scale, which is referenced by CFR 1910.217, Table 0-10. The ANSI scale is more likely to be used by Insurance Loss Control Engineers in manufacturing plants where smaller hand sizes tend to dominate the employee population. Let’s look at the differences in the two designs:


Note that the OSHA scale locks on the 3rd stair-step on the entrance side, and that the tip of the scale does not reach the die, meaning the test is “passed” for that opening size at that distance away. Also note that the ANSI scale locks on the last stair-step on the entrance side, and that the tip of the scale goes past the die, meaning that the test is “failed” for that opening size at that distance away. That problem can be fixed in one of two ways; move the guard a little further away from the die, or make the adjustable guard opening a little smaller, or some combination of those two.

USING A GUARD OPENING SCALE
A Guard Opening Scale is a two-dimensional representative of an average sized finger, hand and arm. Of course, the human body is not two-dimensional but three-dimensional, thus making its correct use critically important. Follow these simple instructions for proper measurements.

First, place the scaled side perpendicular to the smallest dimension in a hole in the barrier guard material and attempt to insert it towards the hazard. If properly designed, the barrier guard will stop the tip from accessing the hazard area. When multiple openings of various sizes exist in a barrier guard, each must be tested with the tool. The maximum guard opening that OSHA allows is a 6-inch opening at 31.5 inches away. For most people that’s armpit to fingertip. Also, the openings should always be measured empty, not with any material in place. This is based on the logic that personnel may put a hand through the guard opening without material taking up a portion of the space. Remember that Safety Inspectors won’t cut a plant operator any slack because the guard happens to be adjustable. Adjustable guard openings must be measured the same as fixed guard openings.

Please call 1-800-922-7533 or visit rockfordsystems.com for more information.

Safeguarding Mechanical Power Presses

Mechanical power presses (a.k.a. punch presses, stamping presses, flywheel presses), have existed in the U.S. since 1857. They were originally designed as either full-revolution, or part- revolution, both of which still exist, although the latter currently represents an estimated 90 percent of the roughly 300,000 mechanical power presses being used in the United States today.

This blog will address part-revolution presses only. These are often referred to as “air clutch” presses, made by dozens of manufacturers. The idea of safety for these machines has existed since 1922, when the first ANSI B11.1 Safety Standard was developed. The latest version, ANSI B11.1-2009 is the 10th update of that standard. This is generally considered to contain the “Best Safety Practices” for press users.

In the early 1970’s, OSHA promulgated a “machine specific regulation” for mechanical power presses, their CFR SubPart O, 1910.217. Very few changes have been made to that regulation since then. Keep in mind that OSHA’s 1910.217 Regulation was taken from ANSI B11.1 using a version that was freshly updated for OSHA in 1971. ANSI has updated their B11.1 four times since that time. Every update adds new, more stringent requirements than the previous version.

Although many companies have long since met the basic OSHA requirements for their presses, a significant number of those shops have yet to make updates to meet the latest ANSI B11.1 Standard. When OSHA regulations came 46 years ago, press control systems were primarily relay-logic systems, designed to meet OSHA’s initial requirement for “Control Reliability” and “Brake Monitoring.”

Press control systems manufactured in the mid 1980’s and beyond have been mostly solid-state, designed to meet the ANSI Standard concept for the “Performance of Safety Related Functions.” One of the advantages to solid-state controls are the features built-into them. Two of these are a: built-in “Stopping Performance Monitor” and built-in “Stop Time Measurement,” which prevents users from having to use a portable device to determine “Safety Distance” when applying Light Curtain and Two-hand Control devices.

Mechanical Power Presses require some combination of guards and/or devices to reduce or eliminate exposure to hazards at the “point of operation” where the dies close. Safeguarding alternatives include: Point-of-Operation Guards, Awareness Barriers, Light Curtains, and Two-Hand Controls.

1) Point-of-Operation Guards
Point-Of-Operation Guards are typically used for continuous operations where coil-stock feeds into the press as it operates in an uninterrupted mode of operation.

By OSHA’s definition, a guard must prevent people from reaching over, under, through, or around it. (OUTA is an acronym easy to remember; This guard keeps you “OUTA” here.) Guards must meet one of two measurement scales (the OSHA guard opening scale or the ANSI/CSA guard opening scale), to ensure that a small hand can’t reach far enough through any opening to get hurt.

To discourage misuse, hinged or sliding guard sections are often electrically interlocked, so that they remain in position (closed) during press operations. Without interlocks, movable sections can easily be left open, whether intentional or not, leaving Operators and others in the area unprotected.

Guard Interlocks are attached to hinged or moving guard sections, since access to the point-of-operation is most often made through those openings. Interlock attachment is best accomplished with tamper-resistant fasteners to discourage cheating the switch.

Many older guards use simple lever-arm or push-button switches. Not only are these switches easy to cheat with tape or wire, they are also spring-operated, leaving them subject to failure it the spring breaks. Newer switches are free of springs, and use actuators with a unique geometry, making them much more difficult to defeat.

2) Awareness Barriers (for low-level hazards only)
Another common method of safeguarding on coil-fed presses is an “Awareness Barrier” (A/B). They should completely surround press auxiliary equipment with railings, chains, or cables, suspended on floor stations. Although they don’t provide the same level protection as a guard, they do help to limit access to hazards on auxiliary equipment like coil-payoffs, feeds, straighteners, etc.

Awareness Barriers are considered superior to just a yellow line on the floor, because to get beyond the A/B requires an intentional act and some physical contact with them. This means the person is well aware that they are entering a hazard area, contrary to their safety training. Auxiliary equipment may also require that ingoing rolls are covered to prevent entanglement with long hair or loose clothing.

Awareness barriers should also have several Danger or Warning signs attached to them specifying what the hazards are in going beyond the A/Bs. Examples of sign verbiage might include: moving coil stock, ingoing pinch points, sharp edges, tripping hazard, etc.

3) Light Curtains
Light Curtains have been around since the mid-1950’s. They consist of a vertically mounted transmitter and receiver with closely spaced beams of infra-red light, creating a flat sensing-field. When fingers, hands, or arms that reach through that sensing-field, the press cycle is prevented or stopped to avoid operator injury.

One of the reasons that presses make a good application for light curtains is that they can be stopped mid-cycle very quickly. Light curtains can be used for either single or continuous applications. The only thing that light curtains don’t provide is “impact protection” should something break in the point of operation and be ejected in the operator’s direction. Where that’s an issue, poly carbonate shields or guards may be appropriate.

Like any safeguarding device, light curtains should be “function-tested” before every operating shift to ensure that they are continuing to provide protection. Make/model specific “function-test procedures” are usually available on each light curtain manufacturer’s website.

4) Two-Hand Controls
Two-Hand Controls are considered a safer means of cycling a press than a foot-switch because both hands must be in a safe position to use them. When cycling a press with a foot switch, hands can be anywhere. When operating a press in the single-cycle mode of operation, it’s possible to use a two-hand control as a safeguarding device as well. This requires that they meet a list of rules in both OSHA and ANSI.

Ten of the basic requirements for a two-hand control being used as a safeguarding device (in the single-cycle mode of operation) include:
1) protection from unintended operation
2) located to require the use of both hands (no elbow & finger tips)
3) concurrently operated (actuation within half-second of each other)
4) holding-time during the downstroke (hazardous portion of cycle)
5) anti-repeat (push and release both actuators for each single cycle)
6) interrupted stroke protection (for all operating stations)
7) separate set of two-hand controls for each operator
8) mounted at a calculated “Safety Distance” from nearest hazard
9) control system to meet “Performance of Safety Related Functions”
10) Stopping Performance Monitor is also required

When running high-production operations, don’t forget to consider ergonomics when choosing and installing two-hand controls. Several manufacturers of low-force and no-force actuators are on the market.

Also required by OSHA on Mechanical Power Presses is an electrically interlocked “Safety Block” whenever dies are being adjusting or repaired while they are in the press. The interlock is required because safety blocks are very seldom designed to hold the full working-force of the press (please refer to our Die Safety Blocks blog for additional information).

Mechanical Power Presses require two types of OSHA inspections:
1) Periodic and regular (typically quarterly) inspections of the press parts, auxiliary equipment, and safeguards . . . (don’t forget to document)
2) Weekly inspections of; clutch/brake mechanism, anti-repeat feature . . . along with other items (don’t forget to document)

OSHA requires training (in 1910.217) for anyone who cares for, inspects, maintains, or operates mechanical power presses.

ANSI B11.1-2009, requires training for “all (people) associated with press production systems, including operators, die setters, maintenance personnel, supervisors, which must also include (OSHA) 1910.147 Lockout/Tagout.”

Please call 1-800-922-7533 or visit rockfordsystems.com for more information.

Got Grinders? Get Safeguarding

Safeguarding Standards for Bench and Pedestal Grinders

Grinders are one of the most frequently cited machines during OSHA machine-safety inspections. This is frequently due to improperly adjusted work-rests and tongue-guards on bench/pedestal grinders, as well as a lack of ring-testing for the grinding wheels.

OSHA 29 CFR SubPart O 1910.215 is a “machine specific” (vertical) regulation with a number of requirements, which if left unchecked, are often cited by OSHA as violations. ANSI B11.9-2010 (Grinders) and ANSI B7.1 2000 (Abrasive Wheels) also apply.

Work-Rests and Tongue-Guards
OSHA specifies that work-rests must be kept adjusted to within 1/8-inch of the wheel, to prevent the workpiece from being jammed between the wheel and the rest, resulting in potential wheel breakage. Because grinders run at such a high RPM, wheels actually explode when they break, causing very serious injury, like blindness and even death.

In addition, the distance between the grinding wheel and the adjustable tongue-guard (also known as a “spark arrestor”) must never exceed 1/4-inch. Because the wheel wears down during use, both these dimensions must be regularly checked/adjusted.

“Grinder safety gauges” can be used during the installation, maintenance, and inspection of bench/pedestal grinders to make sure the work-rests and tongue-guards comply with OSHA’s 1910.215 regulation and ANSI standards. Wait until the wheel has completely stopped and the Grinder is properly “Locked Out” before using a “grinder safety gauge”. Grinder coast-down time takes several minutes, which tempts employees to use the “grinder safety gauge” while the wheel is still rotating. This practice is very dangerous because it can cause wheel breakage.

Where grinders are concerned, personal protective equipment (PPE) usually means a full face-shield, not just safety glasses. You cannot be too careful with a machine that operates at several thousand RPM.

Remember, you must DOCUMENT any and all safety requirements set forth by OSHA, as that is their best evidence that safety procedures are really being followed.

Ring-Testing
OSHA says that you must “ring-test” grinding wheels before mounting them to prevent the inadvertent mounting of a cracked grinding wheel.

Ring Testing
Ring-Testing involves suspending the grinding wheel by its center hole, then tapping the side of the wheel with a non-metallic object. This should produce a bell tone if the wheel is intact. A thud, or a cracked-plate sound indicates a cracked wheel. NEVER mount a cracked wheel.

For larger grinders, grinding wheels are laid flat on a vibration-table, with sand evenly spread over the wheel. If the wheel is cracked, the sand moves away from the crack.

To prevent cracking a wheel during the mounting procedure, employees must be very carefully trained in those procedures. This starts with making sure the wheel is properly matched to that particular grinder, using proper blotters and spacers, and knowing exactly how much pressure to exert with a torque-wrench, just to mention a few things.

This OSHA-compliant “Wheel-Cover” allows no more than 90 degrees (total) of the wheel left exposed. (65 degrees from horizontal plane to the top of wheel-cover)
Never exceed these wheel-cover maximum opening dimensions. Larger wheel-cover openings create a wider pattern of flying debris should the wheel explode. A well-recognized safety precaution on bench/pedestal grinders is to stand well off to the side of the wheel for the first full minute before using the machine. Accidents have shown that grinding wheels are most likely to shatter/explode during that first minute.

There is an OSHA Instruction Standard #STD 1-12.8 October 30, 1978 addressing the conditional and temporary removal of the “Work Rest” for use only with larger piece parts based on the condition that “Side Guards” are provided. If this may apply to your grinder(s), make sure that you read the entire thing on OSHA.gov.

Safety Information
Grinding Wheels are Safe… Use but Don’t Abuse

Do

  • Do always Handle and Store wheels in a careful manner
  • Do Visually Inspect all the wheels before mounting for possible damage
  • Do Make Sure Operating Speed of machine Does Not Exceed speed marked on wheel, its blotter or container
  • Do Check Mounting Flanges for equal size, relieved as required & correct diameter
  • Do Use Mounting Blotters when supplied with wheels
  • Do be sure Work Rest is properly Adjusted on bench pedestal, and floor stand grinders
  • Do always Use Safety Guard that covers a minimum of one-half the grinding wheel
  • Do allow Newly Mounted Wheels to run at operating speed, with guard in place, for at least one minute before grinding
  • Do always Wear Safety Glasses or some type of approved eye protection while grinding
  • Do Turn Off Coolant before stopping wheel to avoid creating an out-of-balance condition

Don’t

  • Don’t use a wheel that has been Dropped or appears to have been abused
  • Don’t Force a wheel onto a machine Or Alter the size of the mounting hole – If a wheel won’t fit the machine, get one that will
  • Don’t ever Exceed Maximum Operating Speed established for the wheel
  • Don’t use mounting flanges on which the bearing surfaces Are Not Clean, Flat And Smooth
  • Don’t Tighten the mounting nut Excessively
  • Don’t grind on the Side of conventional, straight or Type 1 wheels
  • Don’t Start the machine Until the Safety Guard is properly and securely In Place
  • Don’t Jam work into the wheel
  • Don’t Stand Directly In Front of a grinding wheel whenever a grinder is started
  • Don’t grind material for which the Wheel Is Not Designed

Source: Grinding Wheel Institute

Rockford Systems Can Help
Rockford Systems offers a wide variety of safeguarding products for grinders.

Grinder Safety Gauge

Bench Grinder Safety Gauge
The bench grinder safety gauge is laser-cut, Grade 5052 aluminum with H32 hardness. The safety yellow, durable powder-coated gauge has silk-screened text and graphics. The bench grinder safety gauge measures 2 3/4-inches wide by 2 1/4-inches high by .1000-inches thick and has a 1/4-inch hole for attachment to the bench grinder.

Standard Mount Grinder Shields
These standard mount grinder shields are available in various sizes for protection from the swarf of bench or pedestal grinders. The frames are constructed of reinforced fiber nylon or heavy cast aluminum. Each shield is furnished with a threaded support rod. The transparent portion of the standard mount grinder shields is made of high-impact resistant polycarbonate to minimize scratching and provide durability.

Direct-Mount or Magnetic-Mount Bench Grinder Shields with Flexible Arms

Double-Wheel and Single-Wheel Bench Grinder Shields
Double-wheel bench grinder shields provide protection for both wheels of the grinder with one continuous shield. The durable shield is made of clear, 3/16-inch-thick polycarbonate and measures 18-inch x 6-inch. A special shield bracket adds stability to the top of the shield. The single-wheel bench grinder shield is made of clear, 3/16-inch-thick polycarbonate and measures 6-inch x 6-inch. This sturdy, impact-resistant shield is designed for use when a single wheel needs safeguarding. These shields have a direct-mount base that attaches directly to the grinder table or pedestal.

Electrically-Interlocked Grinder and Tool Grinder Shields
Electrically Interlocked Grinder and Tool Grinder Shields
These electrically interlocked grinder and tool grinder shields are ideal for single- and double-wheel grinders. When the heavy-duty shield is swung out of position, the positive contacts on the microswitch open, sending a stop signal to the machine control. The safety microswitch electrical wires are furnished with a protective sheath and connect to the safety circuit of the machine that switches off the control to the movement of the grinding wheel. All safety micro switches are mounted in an enclosed housing with an enclosure rating of IP 67. The multi-adjustable, hexagonal steel arm structure allows easy mounting on the most diverse grinders. A versatile clamp allows horizontal and vertical adjustment of the shield. All electrically interlocked grinder and tool grinder shields consist of a high impact-resistant, transparent polycarbonate shield with an aluminum profile support and provide operator protection from flying chips and coolant.

Single-Phase Disconnect Switch

Single-Phase Disconnect Switch and Magnetic Motor Starter
This single-phase unit is designed for motors that have built-in over-loads. Typical applications for these combinations include smaller crimping machines, grinders, drill presses, and all types of saws. The 115-V, 15-A disconnect switch and non-reversing magnetic motor starter are housed in a NEMA-12 enclosure. Enclosure size is 8″ x 6″ x 3 1/2″. It includes a self-latching red emergency-stop palm button and a green motor control start push button. It can be used on machines with 115-V and is rated up to 1/2 HP maximum. The disconnect switch has a rotary operating handle which is lockable in the off position only. This meets OSHA and ANSI standards. For machines with 230-V AC single-phase motors, a transformer is required to reduce the control circuit voltage to 115-V AC in order to comply with NFPA 79.

Danger Sign for Cutting and Turning Machines
Don’t forget to post the appropriate danger signs near all machinery in the plant. The purpose of danger signs is to warn personnel of the danger of bodily injury or death. The suggested procedure for mounting this sign is as follows:
1) Sign must be clearly visible to the operator and other personnel
2) Sign must be at or near eye level
3) Sign must be PERMANENTLY fastened with bolts or rivets

Please call 1-800-922-7533 or visit www.rockfordsystems.com for more information.

OSHA Inspection Priorities

The following is an excerpt taken from OSHA Fact Sheet DEP FS-3783.

OSHA inspectors are experienced, well-trained industrial hygienists and safety professionals whose goal is to assure compliance with OSHA requirements and help employers and workers reduce on-the-job hazards and prevent injuries, illnesses, and deaths in the workplace. Since OSHA cannot inspect all 7 million workplaces it covers each year, the agency focuses its inspection resources on the most hazardous workplaces in the following order of priority:

1. Imminent danger situations—hazards that could cause death or serious physical harm receive top priority. Compliance officers will ask employers to correct these hazards immediately or remove endangered employees.

2. Severe injuries and illnesses—employers must report:

  • All work-related fatalities within 8 hours.
  • All work-related inpatient hospitalizations, amputations, or losses of an eye within 24 hours.

3. Worker complaints—allegations of hazards or violations also receive a high priority. Employees may request anonymity when they file complaints.

4. Referrals of hazards from other federal, state or local agencies, individuals, organizations or the media receive consideration for inspection.

5. Targeted inspections—inspections aimed at specific high-hazard industries or individual workplaces that have experienced high rates of injuries and illnesses also receive priority.

6. Follow-up inspections—checks for abatement of violations cited during previous inspections are also conducted by the agency in certain circumstances.

Normally, OSHA conducts inspections without advance notice. Employers have the right to require compliance officers to obtain an inspection warrant before entering the worksite.

Click here for a full PDF version of OSHA Fact Sheet DEP FS-3783.

Do I Really Need to Safeguard My Machines?

Unguarded Lathe

Yes, you really do need to safeguard machines in your workplace. But to what extent can be a matter of interpretation based on minimum safety requirements (OSHA regulations), or best safety practices (ANSI standards).

Most employers are familiar with OSHA (Occupational Safety & Health Administration) and the enabled OSH Act of 1970. Under the OSH Act, employers are responsible for providing a safe and healthful workplace. Employers must comply with all applicable OSHA standards. Employers must also comply with the General Duty Clause of the OSH Act, which requires employers to keep their workplace free of serious recognized hazards.

By law, employers are legally required to follow OSHA regulations. That means an OSHA inspector will issue citations for noncompliance to their CFR (Code of Federal Regulations). OSHA’s CFR SubPart O—Machinery and Machine Guarding has six (6) machine specific safeguarding regulations which are:

1910.213 Woodworking Machinery
1910.214 Cooperage Machinery

1910.215 Abrasive Wheel Machinery
1910.216 Mills and Calendars
1910.217 Mechanical Power Presses

1910.218 Forging Machines

safeguarded lathe

OSHA regulations for safeguarding most other machines falls under 1910.212 General Requirements For All Machines which specifies that the operator and others in the machine area be protected from exposure to hazards.

However, ANSI’s B11-Series Safety Standards (which has 24 machine categories) are often used to fill in the details for specific safeguarding and can be used as reference material by OSHA inspectors. Even though ANSI safety standards are voluntary, they could become legally mandatory if an OSHA citation mentions specific ANSI standard for you to comply to.

The bottom line is that all employers should strive to exceed minimum requirements and abide by the best safety practices found in the ANSI B11 standards. The key to employee safety is to observe best safety practices at all times. After all, it could be a matter of life and death!