OSHA & Light Curtains

Higher safety standards for machinery are emanating from trade agreements.

• By Robert Thomson
• May 01, 2003

THE first in what appears to be a long stream of international machine safety standards was adopted recently by the United States. This standard (IEC-61496, parts 1 & 2) is a product standard for Electro Sensitive Protective Equipment, adopted as ANSI/UL 61496 parts 1 & 2. It deals with the electrical and functional safety aspects for safeguards that sense the presence of a person; such as light curtains, laser scanners, and optical actuators. Prior to this standard being adopted by the United States, there were no U.S. requirements for the design and construction of these machine safeguards.

OSHA was asked, Now that the U.S. has a standard for this type of safeguarding device (that is, light curtains), does 29 CFR 1910.212 now kick in? 29 CFR 1910.212 states, "point of operation safeguarding devices shall comply with any appropriate standard. . . ."

OSHA's Directorate of Compliance Programs put forth a decision on June 5, 2001, in an "interpretive letter." It stated that:

• Light curtains must comply with IEC-61496 parts 1 & 2 adopted as ANSI/UL 61496 parts 1 & 2.
• Light curtains' "TYPE" (i.e., their Safety Performance Level) must be appropriately selected.
• Light curtains' optional functions, as listed in Annex "A" of IEC-61496 part 1, must comply with Annex "A" requirements.
• Light curtains must be properly integrated into the machine.
• Light curtains must be certified by independent third party.

Coming soon is OSHA's Draft Proposed Safety and Health Program Rule, 29 CFR 1900.1 (Docket No. S&H-0027), which has the stated purpose of reducing the number of job-related fatalities, illnesses, and injuries. This rule would accomplish this by requiring employers to establish a workplace safety and health program to ensure compliance with OSHA standards and the General Duty Clause of the Act (Section 5(a)(1)).

Compliance Identification Made Easy
Light curtains complying with the standard must state on their product label:

• Standard IEC-61496 parts 1 & 2 (TYPE 4)
• Certification Number, and
• Certifying Body.

The machine's risk assessment and hazard abatement documentation should contain the light curtain certification by independent third party.

Some light curtain manufacturers are claiming certification to a draft European standard, prEN 50100--1 & 2, is equivalent. This is false.

GATT and Trade Agreements
At the 1994 Uruguay Round of the General Agreement on Tariffs and Trade (GATT), it was agreed to "level the playing field" by eliminating "technical barriers to trade." The World Trade Organization (WTO) was empowered to eliminate these barriers by establishing international standards for products, services, and processes, which each country would adopt as their national standards, thereby leveling the playing field. "Technical barriers to trade" are usually country-specific requirements for product entry and are based on health, safety, and the environment.

To implement this process, the International Standards Organization (ISO) and the International Electrotechnical Commission (IEC) were assigned the task of developing global consensus standards that each signatory country to GATT would harmonize as their national standards. Because these standards deal with health, safety, and the environment that often are integrated into nations' regulatory process and because nations are not willing to lessen their standards that support regulation, the standards are usually written at a very high Safety Integrity Level (SIL), thus raising the safety bar for all nations.

Canada is harmonizing its national standards with global machine safety standards, and Ontario Regulation 528/00 requires compliance. (See Chart 1 for a list of standards.)

Adoption as National Standards
For the "Machine Safety Sector," new safety standards are now being released by ISO and IEC and being adopted at the national level. Both the United States and Canada are currently adopting many of these international standards as their national standards--that is, ANSI and CSA standards.

These international machine safety standards are structured in a hierarchy. Each lower level of standards in the hierarchy must support the intent of the higher standard. The standards that are being accepted first are in the areas where national standards have voids--"A" and "B" standards.

These standards cover both electrical safety and functional safety. (Functional safety is the manner in which the safety function will be affected under adverse conditions, such as fault conditions, environmental conditions, electromagnetic interference, electrical disturbances, and others.)

These international standards were developed to a very high level of safety, both for the safeguarding products and their integration into the machine control. In addition, there are very rigorous requirements for the design, development, and architecture of both hardware and software when the software performs a safety function. (See IEC-61508 part 1-7, Functional Safety of the Electrical/Electronic/Programmable Electronic Safety Related Control System.) For machine safety,the targeted "probability of dangerous failure" is 10^-4 years. This is a quantum leap forward in safety.

Few, if any, machine safeguarding devices designed before these stringent standards were in place comply with these new standards. Few safeguarding devices currently being marketed comply with these new standards. (Note that, for existing machinery, if the safeguarding device does not comply with current applicable standard then it must be modified.) In fact, standard IEC-61496 for light curtains was written at such a demanding level that no manufacturer worldwide complied.

The international community developed IEC-61496 parts 1 & 2 as a performance-based standard for light curtains because of an inordinate number of safety light curtains "failing to danger," with injury/death resulting. The standard requires light curtains to maintain their safety function when subjected to adverse conditions, such as fault conditions, electrical disturbances, electromagnetic interference, RF interference, ambient light interference, and many other environmental conditions.

Due Diligence
Machine builders and machine users are required to perform their "due diligence" in assessing and abating hazards. At a minimum, this means compliance with OSHA standards.

Proving in a court of law you have done your "due diligence" will require documented evidence that a "Risk Assessment and Hazard Abatement" analysis has been performed. The "due diligent" documentation must demonstrate that all hazards have been addressed and abatement means are to the "state of the art," which is interpreted as compliance with globally accepted machine safety standards.

At the core of the machine safety process is this requirement to perform and document the "Risk Assessment and Hazard Abatement Means." This is a five-step iterative process. For the integration of safeguarding devices, the risk assessment standard defers to IEC-62046, Safety of Machinery - Application of Presence Sensing Protective Equipment to Machinery, which pertains to:

• Light curtains
• Single beam devices
• Laser scanners
• Safety mats
• Passive infrared devices
• Interlock doors
• Interlock guards
• Moving plate or bar
• Pressure-sensitive edges or bumpers
• Enabling devices, and
• Holding to run control.

Quality System Audits
The latest editions (released in 2000) of the quality management standards ISO 9000 and QS 9000 have included requirements for safety auditing. These audits are mandatory when there are regulations in place where non-compliance could result in shutdowns that affect deliveries.

For auditors to approve compliance with safety regulations, they require "audit evidence," which starts with the "Risk Assessment with Hazard Abatement" document. The abatement means must be tied back to national or international product safety standards and their integration standards. The "Safety Audit" is verification that the five steps of the "Risk Assessment and Hazard Abatement" were conducted and provides "audit evidence" to substantiate compliance.

Labeling
Within the international product safety standards, there is the requirement for manufacturers to state on their product label, affixed to the safety device, the product standard(s) they are claiming compliance to and the method used to make the claim of compliance--i.e., third-party certified by competent body authorized by a government. In such cases, the third-party organization and certification number shall also be affixed to the device. If these markings are not on the product label, it will undoubtedly result in non-conformity.

For example:

Where these markings are on the product label, the auditor will require the risk assessment documentation to support the claim whereby the product certification should be on file.

Also within the international product safety standards is a requirement for the manufacturer to provide "Instructions for Safe Use." These generally take the form of "warnings" of what not to do. These warnings must be complied with; otherwise, the integration of the product cannot demonstrate that it was installed in accordance with the manufacturer's instructions.

Read the manufacturer's instruction manual prior to selecting a safeguarding device. Why? Did you know that most light curtain manufacturers:

• Warn against having their detection zone closer than 100 mm (4.1") from surfaces that can reroute their light beam(s).
• Warn that you must implement their "Machine Test Signal" (i.e., the signal to test the light curtain) yet provide bypass switches.
• Warn to monitor all elements in the machine stopping circuit.
• Warn to add the time of monitoring for all elements in the machine stopping circuit to the overall response time used for calculating the safety distance.

Spotting Deceptive Claims
It is the law that the machine safety integrators perform their due diligence as specified. To achieve this, they must beware of deceptive claims. Look out for the use of language, such as the manufacturer stating:

• Designed to meet the requirements of standard xyz.
• Conforms to the requirements of standard xyz.
• Complies with the requirements of standard xyz.

These are opinion statements.

Look for:

• Certified to standard xyz.
• Certified by abc to standard xyz.

Or, the manufacturer may state:

• It is CE marked.
• CE mark is not a certification mark.
• CE mark is not a safety mark.
• CE mark is not a conformity mark that the product conforms to a standard.
• CE mark is a Manufacturer's Mark.

The manufacturer may provide a Declaration of Conformity (DoC) in lieu of a certificate.

• The DoC is a document produced by the manufacturer.

The DoC is not certification.

Or, the manufacturer provides certification.

• But it is to a defunct standard.

Example: For a light curtain, provides certification to prEN50100 instead of IEC-61496 parts 1 & 2 and claims equivalency.

• But it is to the wrong standard.

Example: For a light curtain control, provides certification to EN954 instead of IEC-61496 parts 1 & 2.

• But it is to a partial standard.

Example: For a light curtain, provides certification to IEC-61496 part 1 but not to part 2.

• But it is to no standard.

Example: For a light curtain, provides certification to the European Machinery Directive.

Look out for misappropriating the safeguarding device's safety contribution; it must be commensurate with the level of risk it is to offset. Note that, because of the sensing technique and fault detection capabilities, some safeguarding devices can obtain only a certain level of safety contribution called TYPE or Category, with TYPE 4/Category 4 being the highest integrity.

This article originally appeared in the May 2003 issue of Occupational Health & Safety.