ETMS2.com

Lift Safety

Purpose
As the semiconductor industry moves toward the use of larger manufacturing tools, processing 300mm wafers, the components that make up these tools are becoming larger and heavier. To accommodate these larger components, lifting aides are needed to ensure that servicing these systems can be accomplished in an ergonomically safe manner. Lift systems (overhead hoists, lead-screw lifts, etc.) must be specifically designed to accommodate the application in question, as system configurations oftentimes preclude the use of previously developed, commercially available crane systems. As heavy loads will be manipulated by these systems, their design must be evaluated to ensure safety.

To this end, Earth Tech Microelectronic Services offers lift system safety evaluations. Applicable industry standards and good safety engineering practice is used to evaluate lift system design and application. Earth Tech Microelectronics has a highly qualified mechanical engineering product safety staff to support this function. In addition, Earth Tech Microelectronics offers the services of certified ergonomists, electrical engineers, and compliance engineers to ensure that all applicable safety and compliance issues are addressed.

As lift systems are relatively new to the semiconductor industry, their design and particularly the conformance requirements to SEMI S2 are still in the process of being developed. As a direct result, the conformance requirements as detailed below are still in the development process and are subject to change.

Applicable Standards
In an effort to conduct the most thorough and useful evaluation of lift systems, Earth Tech has referenced various industry standards and extracted the applicable sections. Standards referenced include:

ASME B30 & B56
OSHA 1926.552, 1926.554, 1910.179
EN 98/37/EC of the European Parliament (Machinery Directive)
SEMI S2 & S8
ANSI A10.5
AWS D14.1
CMAA No. 74

Not all of the information contained in these standards is applicable to lift systems built for the semiconductor industry. Earth Tech has used sound engineering judgment in selecting which pieces of which standard apply to the systems being evaluated. One general rule was to use the most stringent requirement from the selected standards to ensure that the system will meet the basic requirement of all the standards.

Design Requirements

In the case of an overload, the failure point of the lift system must be known and benign.

This requirement is used to ensure conformance with SEMI S2-0200 paragraph 6.5 (the single-point-failure clause). In the case of an overload, the lift system must have some provision to prevent it from attempting to destroy itself. This can be a load-limiting circuit breaker or mechanical clutch.

The structure or housing that supports the hoist must have an appropriate factor of safety based on the average ultimate material strength. For hand chain operated hoists a factor of safety of 4 is required while for electric- or air-powered hoists a factor of safety of 5 is required.

This requirement is used to ensure that the lift system is structurally sound and is capable of performing all lifting operations safely. To demonstrate conformance to this requirement, appropriate calculations or test results must be provided for review. In common with other areas of S2, it is not a requirement that calculations/analysis be performed or reviewed by a professional engineer. This requirement will apply to all structural members that support the hoist. In general, if a lead screw is used rather than a drum-hoist, the factor of safety of 5 (based on material ultimate strength) will also apply.

The device used to attach the load to the hoist¹s wire, rope, or chain (the load attachment device) must be designed to withstand the stresses imposed by the rated load plus the weight of itself with a minimum design factor of three, based on the yield strength of the material.

This requirement applies to all devices used "below the hook" for attaching the load to the hoist rope, wire, or chain. If the load attachment device is used to lift more than one load, the factor of safety of 3 is based on the heaviest load to be lifted. To demonstrate this requirement, appropriate calculations or test results must be provided for review. In common with other areas of S2, it is not a requirement that calculations/analysis be performed or reviewed by a professional engineer.

The other load bearing components of the lift system must also have appropriate factors of safety. The factor of safety is based on the rated load, as defined above, and the average ultimate strength. The minimum safety factors are:

     -Ropes: 7
     -Rope Ends: 5
     -Chains: 4
     -Slings: 4 for steel chain slings and 5 for all other material slings.

To demonstrate conformance to this requirement, appropriate calculations or test results must be provided for review. In common to other areas of S2, it is not a requirement that calculations/analysis be performed or reviewed by a professional engineer. If these components are purchased from an equipment supplier, vendor specifications of rated load (equal to the applicable safety factor times the load to be lifted) is acceptable to demonstrate that this requirement has been met.

If it is intended that a load will be stored in an elevated position, appropriate lockout/verification measures must be employed. OSHA dictates that employees shall be kept clear of suspended loads. In order to accommodate this requirement, some method of fixing the load to a load bearing structure other than the hoist chain or rope must be employed.

In some cases, the load is simply lifted straight up and then work is performed under the load. In this case, some means of securing the load to a structural support other than the hoist chain, rope, or cable must be used to comply with the OSHA standards.

Testing Requirements

Each lifting system prototype and load attachment device prototype will undergo a static load test of 150% of the rated load for no less than two minutes. After the test is complete, the lifting system and load attachment device should be visually inspected for signs of yielding.

This test is conducted to ensure that the lift system and load attachment devices are structurally sound. Deflection of the structure should be minimized to the greatest extent possible and permanent deformation should not occur. After the test is conducted, the structure is visually inspected for signs of yielding.

Each lifting system prototype will undergo dynamic load testing at 110% of the rated load. Two tests are proposed: an operating evaluation and a cycle test.

Operating Test
The lifting system, loaded at 110% of the rated load, needs to be setup for an operating evaluation. This test should include the load attachment device.

Cycle Test
The proposed test requirement is the lifting system and load attachment device, loaded at 110% of the rated load, be cycled the number of times equal to the number of times it has been designed to be used in the field throughout its lifetime. This number, and its justification, needs to be identified in writing by the manufacturer. This testing will include both horizontal and vertical motion, although the two motions can be isolated. The lift system will then be inspected for signs of fatigue or wear.

The operating test is meant to demonstrate that the lift system and load attachment device are rigid enough to perform their desired tasks even when loaded at more than the rated load. The lift system function is demonstrated at 110% of rated load. This is also an opportunity to demonstrate the ergonomic acceptability of lift use, although this can be done separately.

The cycle test is conducted to show that the lift system is adequately designed to function throughout its lifetime. As these tools can have long lifetimes (over 10 years) this is important to show that the effects of fatigue and wear have been accounted for. It is not the intent just to cycle the hoist motor if it has already been purchased with appropriate documentary proof of reliability. The structures can be isolated and tested separately if appropriate. Testing is done at 110% of rated load to further demonstrate that the lift structure (used at rated load) is adequate to survive use throughout its lifetime.

Labeling Requirements

The lifting system will be permanently labeled and this label will include the manufacturer¹s name and address, serial number, and the rated load. This does not include the appropriate hazard warning labels that will also need to be included on the lift system.

This nameplate is required to allow tracking of the lift system. If the serial number of the tool to which it is attached is to be used for tracking, the lift system must still be labeled with the rated load.

All hazard labels shall conform to ANSI Z535.4. Hazard labels should include cautions against:
lifting more than the rated load;
operating the hoist when the load is not centered under the hoist;
operating the hoist when the rope is twisted, kinked or damaged;
lifting people;
lifting loads over people;
operating the hoist when the rope is not properly wound on the drum

.

These hazard-warning labels are included as examples of specific mechanical hazards associated with lifting operations. Each lift system will have to be examined to determine which hazard warning labels are appropriate. If ergonomic or electrical hazards are present, these will have to be identified as well.

The load attachment device will be permanently labeled and this label will include the manufacturer¹s name and address, serial number, and the rated load

.

This is for the case when multiple load attachment devices are to be used with one lifting system. In the case when one load attachment device is used (and never removed from the end of the wire, rope, or chain) this is not necessary. For convenience, the load attachment device should also be labeled with an indication of what it is intended to lift (i.e. chamber liner).

Manufacturing Requirements

6.1 Every lift system, not just the prototype, will be statically and dynamically tested. For the static test, the lift system shall be loaded at 125% of the rated load for two minutes. For the static test, the lift system shall be loaded at 110% of rated load and the load shall be lifted and lowered. While this test is conducted, the smoothness of the drive through to the load should be observed as well as the functionality of the upper limit stop. If the testing cannot be performed by the manufacturer, the procedure for performing the static and dynamic tests, and instruction to perform the test before putting the lift system into service, shall be included in the installation manual that will accompany the lift system. A test certificate, that includes the serial number, verifying that the system has been proof tested, should be generated and retained.

In the case where the end-user will assemble/install the lifting system, the manuals need to include instructions to conduct the tests and appropriate procedures for performing them. The manuals, including these test instructions, need to be provided to Earth Tech for review. When the lift system is assembled and installed by the manufacturer during manufacturing and integration, it is recommended that the static and dynamic test procedures be included in the final test procedure/quality assurance plan and verified by a qualified person in order to meet the OSHA requirements.

Every mode of operation of every load attachment device, not just the prototype, will undergo a static load test of 125% of the rated load. After the test, a qualified person shall inspect the device for deformation, cracks, or other defects and a written QA report shall be furnished. A test certificate, that includes the serial number, verifying that the system has been proof tested, should be generated and retained.

Provision of the Quality Assurance Plan or Final Test Procedure, including this test requirement, should be provided for review.

Documentation Requirements - Operation

The manual should include the requirement that end-user technicians be trained by the manufacturer or qualified personnel in the safe use, inspection, and maintenance of the stationary lift system and load attachment device or be trained by other end-user trained and designated end-user technicians.

This is a basic requirement similar to that required by section 14.1 of SEMI S13. The intent is to notify the end user that lift system operation should only be conducted by those users who have read and understand the instructions in the operation manual. Earth Tech will accept a statement of the above in the manual including reference to the specific sections of the manual that detail the operating and maintenance requirements.

The manual should include a description of the service for which the lift system and load attachment device has been designed. This should include a functional description of the lift system, its designed use, and intended conditions, including rated load, intended usage, and life.
The manual should include a description of the service for which the lift system has been designed including intended use, rated load, life expectancy, and designed use.
The safe procedure for use of the stationary lift system needs to be documented in the manuals. This should include:
The following warnings: not to exceed the rated load of the lift system; not to move the load over people;
not to handle any load for which the lift system is not designed;
that the operator shall not ride or allow other people to ride on the lifting system.
How the load is attached to the lift system, including ensuring that the ropes or chains are not kinked, or twisted around each other.
Direction to put down the load or store it in the raised position using the locking mechanism, as appropriate, before moving on to the next step of the procedure, or leaving the tool.

Earth Tech recommends that the correct use of the lift system, including the appropriate cautions and warnings, be integrated into the procedure for which the lifting is necessary.

Documentation Requirements - Inspection

Details regarding inspection of the lift system should be included in the manual. These inspections are required, as applicable, for all lifting systems. Inspection will be split into two different intervals, frequent and periodic. Frequent inspections will be made monthly and periodic inspections will be made yearly.
Frequent inspections are visual examinations made by the operator and written records are not required. All lifting systems shall be inspected frequently (monthly) to look for:
operating mechanisms for proper operation, proper adjustment, and unusual sounds;
signs of distortion, wear, and cracks or gouges on the brackets;
proper actuation of the safety latch when the lid reaches the top of the lift;
signs of distortion, corrosion, and broken strands on the ropes;
Periodic inspections are visual examinations made by an appointed person who must prepare a dated inspection report. All lifting systems shall be inspected periodically (yearly) to look for:
the items listed in the frequent inspection interval;
fasteners for evidence of loosening;
load blocks, suspension housing, hand chain wheels, chain attachments, clevises, yokes, suspension bolts, shafts, gears, bearings, pins, rollers, and locking and clamping devices for evidence of wear, corrosion, cracks, and distortion;
hook retaining nuts or collars, and pins, welds, or rivets used to secure the retaining members for evidence of damage;
load sprockets, idler sprockets, drums, and sheaves for evidence of damage and wear;
the motor brake and load brake for signs of wear;
electrical apparatus for evidence of pitting or deterioration of controller contacts;
supporting structure or trolley, if used, for evidence of damage;
label or labels for legibility;
end connections of wire ropes or load chains for evidence of wear, corrosion, cracks, damage, and distortion;
reduction of rope diameter below nominal diameter due to loss of core support and severely corroded or broken wires at end connections on the rope;
function labels on pendant control stations for legibility;
the hoist and hoist mounting for evidence of missing items.

These inspections will have to be made it a safe manner. In many cases, the lift system is raised off the floor and inspecting the various components and connections requires the user to be at an extreme height. Care must be taken to ensure that the user can inspect the lift system safely. Fall protection provisions may have to taken. The accompanying documentation will have to instruct the user to make these inspections at the appropriate interval.

Details regarding inspection of the load attachment device should be included in the manual. These inspections are required, as applicable, for all load attachment devices. Inspection will be split into two different intervals, frequent and periodic. Frequent inspections will be made monthly and periodic inspections will be made yearly.
Frequent inspections are visual examinations made by the operator and written records are not required. All load attachment devices shall be inspected frequently (monthly) to look for:
structural deformation, cracks, or excessive wear
loose or missing guards, fasteners, covers, stops, or nameplates
misadjustments interfering with operation on all functional operating mechanisms and automatic hold and release mechanisms
Periodic inspections are visual examinations made by an appointed person who must make written records or an external code mark on the lifter. All load attachment devices shall be inspected periodically (yearly) to look for:
loose bolts or fasteners
cracked or worn gears, pulleys, sheaves, sprockets, bearings, chains, and belts
excessive wear of friction pads, linkages, and other mechanical parts
excessive wear at hoist hooking points and load support clevises or pins.

These inspections can usually be made at a safe location (this will have to be verified). The accompanying documentation will have to instruct the user to make these inspections at the appropriate intervals.

Documentation Requirements - Maintenance
9.1 Details regarding maintenance of the lift system and load attachment device need to be included in the manual. Any hazards that are identified during an inspection need to be corrected before the system can be used again. In addition, a preventative maintenance program should be established. Preventative maintenance should include instructions regarding lubricating the lift system, if applicable. Details regarding maintenance procedures, particularly safe practices during maintenance activities, need to be included. Maintenance procedures should include instructions to:

remove the load from the lift system;
place all controllers in the off position;
lockout and tagout the lift system;
if overhead maintenance work will present a hazard, place warning signs and barriers on the floor beneath the hoist; and
reinstall all guards and safety devices when the maintenance is complete.

The documentation also needs to include the requirement to test the system when significant repairs or modifications have been made. The end user needs to be notified in the manual that any modifications to the system need to be approved by the manufacturer before the lift system can be put back into service.
A preventative maintenance schedule and procedure should be included in the accompanying documentation. These maintenance tasks will need to conform to the requirements of SEMI S8. If applicable, the preventative maintenance procedures should include reference to the safe maintenance procedure as indicated above.
A description of the lockout/tagout procedure for locking out hazardous energies should be included in the manuals and the user should be instructed to follow them before any maintenance work is done.
The manual should explicitly call out that if any hazards are identified in an inspection activity that the lift system should not be used until that hazard has been eliminated. A means of eliminating the hazard also needs to be identified. This maintenance requirement should be easily identified as the appropriate action if a hazard is identified during an inspection.
The manual should call out that modifications to the lift system need to be approved by the manufacturer before the lift system can be put back into service.