CLICK IMAGE TO ENLARGE (+)
The first safety standard written specifically to cover sheet-extrusion equipment was published in August 1999 by the American National Standards Institute (ANSI) in N.Y.C. The ANSI/SPI B151.20,1999 standard was originally developed by the SPI Machinery Div. in Washington, D.C., and then submitted to ANSI for adoption as a national consensus standard. Until now, sheet extrusion lines have been covered only by a basic safety standard on extruders.
The new standard relates to the design and use of the take-off equipment. Its biggest impact will be to require older sheet roll stacks to be extensively rebuilt or replaced in order to meet new emergency nip-opening requirements. Although ANSI is not a government agency, its standards are used as guidelines by OSHA inspectors, and noncompliance can trigger a safety citation or a fine. If an accident occurs, an employer whose equipment violates safety standards may pay higher damages.
Other extrusion processes have had their own specific safety standards since the 1980s. Some of these were updated in August 1999: ANSI/SPI B151.2,1999 for cast film, coating, laminating, and embossing; and ANSI/SPI B151.4,1999 for blown film. ANSI/SPI B151.5,2000 for film and sheet winding equipment was adopted in August 2000.
Emergency nip opening
The most significant change in the standard for sheet processors is the requirement that nips on their polishing-roll stands must open within 3 sec of pushing an emergency button. "For 20 years, the industry built roll stands with a 1-in. nip gap and no opening movement," notes Frank Nissel, president of Welex Inc., Blue Bell, Pa. "If processors pay attention to the new rules, those will all have to be replaced." A lot of older machines are still in operation with roll stacks that can't be rebuilt to comply with the new standards.
The new sheet standard will be mandatory for all new and rebuilt sheet extrusion lines delivered after August 2000 and will be required on all existing machinery by August 2002. (Existing winders will have to meet the new film and sheet winder standard by August 2003.)
The following provisions of the new sheet standard will have the most impact on processors, according to Donn C. Lounsbury, president of D.C.L. Solutions Inc. in Walpole, N.H. Lounsbury chaired the ANSI/SPI committee that developed the new standard.
1. Nips must open 4 in. within 3 sec of an emergency stop signal. An exception is made for existing machinery that opens at least 3 in. within 3 sec. Nips operated by screw jacks will have to be extensively rebuilt to meet the 4-in./3-sec opening requirement. Also, primary nips must stop rolls from turning within a prescribed length of travel.
2. Nips must be guarded, including the primary nips. However, that guarding function can be provided by the die, end extensions or deckles, and by presence-sensing devices. Processors often run webs narrower than a roll stack without bothering to install deckles on the ends of the die. That's a violation, Lounsbury notes.
3. Nips require a pre-close alarm, unless the control is local to the nip. If hand feeding of the web is needed under some processing conditions, nips may rotate at slow speed with the guard open and the nip closed, provided there is a local "deadman" switch, possibly operated by a second operator in the immediate vicinity.
4. Specific warnings are required when an operator moves into areas where he/she could get entangled with surface-winder nips or center-winder lay-on roll nips. Stepping farther into the unloading area of a winder must stop any motion other than continued web winding, such as turret indexing or knife travel.
5. Two independent mechanisms are required to hold winding shafts in chucks.
6. For manual web cutover, the employer is required to have two operators at the cutover position: one to transfer a web to a rotating shaft, the other to stand by the E-Stop button in case the first worker gets entangled.
7. Employers are required to train operators before assigning them to work on a sheet line in order to ensure that correct procedures are employed. They are also required to make machinery instructions available to operators and also to evaluate the need for personal protective equipment and ensure its use where needed.
8. Employers are required to establish a program of periodic and regular inspection of machinery to ensure that safeguards are in proper operating condition and properly adjusted.
While these aren't all the provisions of the new sheet-equipment safety standards, they are the most critical ones that processors must integrate into their existing machinery, Lounsbury says. On the other hand, he cautions, "A partial outline isn't adequate to evaluate compliance with the standard. Processors must obtain and apply the entire standard."
A plan for action
A logical first step for sheet processors is to get a copy of the new standards and audit their lines against the requirements to uncover any non-compliance. Once hazards are identified, their severity can be ranked using EN 1050, a European Community standard methodology.
"It's often true that 80% of the benefits of any endeavor may be obtained with 20% of the effort," Lounsbury notes in a paper on prioritizing hazards given at the SPE ANTEC 2000 conference last year. "The question is how to get 80% hazard reduction with 20% effort. This is where EN 1050 is an excellent guide. It establishes a quantitative evaluation of the degree of risk to personnel from each hazard."
Here's how EN 1050 works.
First: Set up a multi-disciplinary hazard-evaluation team that is familiar with the machinery and its operation.
Second: The team identifies potential hazards to workers, such as crushing, shearing, cutting, or burning.
Third: Each member of the team rates on a scale of 1 to 9 the frequency of worker exposure to each hazard, the severity of probable injury, and worker vulnerability to an accident (see table). Ratings should consider workers' skill level and training, foreseeable misuse of equipment, and environmental or stress conditions such as demands for higher output.
Fourth: Develop a consensus rating for each hazard. Resolve any widely divergent ratings until they differ by no more than one point, and then average the team's ratings for each hazard.
Fifth: Multiply the team's average rating for frequency by that for severity and then multiply that result by the ranking for vulnerability. The possible range of results varies from 1 x 1 x 1 = 1 to 9 x 9 x 9 = 729. The resulting number provides a relative rating with which to prioritize efforts to minimize hazards in the plant.
Lounsbury says this gives processors a tool to find and eliminate their worst hazards first. "The next step is examining whether each hazard can be designed out, and if not, why not. If it can't be designed out, can it be guarded against? And if it can't be guarded against, then warn against it," Lounsbury concludes.
All the standards cited above, including EN 1050, are available from Global Engineering Documents in Englewood, Colo. (www.global.ihs.com). Fore more information call SPI at (202) 974-5230. Or you can contact ANSI directly at (212) 642-4900.blog comments powered by Disqus