Medical Device Link.

Originally Published PMPN November 2005

News

Dust Is an Explosive Problem

Stephanie Steward

Massive explosions at two facilities in 2003 caused the deaths of 13 people. One explosion was at West Pharmaceutical Services’ facility in Kinston, NC, where it manufactured rubber drug-delivery components such as syringe plungers and vial seals.

The incidents highlighted the need to address combustible-dust hazards. Any facility using a potentially combustible dust such as polyethylene or powdered zinc stearate, which are both found in antitack agents, is at risk. And a general lack of hazard recognition by companies and inspectors appears to be undermining what few standards are in place to prevent such tragedies, say investigators of the explosions.

Five simultaneous conditions are required to cause a dust explosion: combustible dust (acts as the fuel; must be of sufficiently small particle size), an oxidizer (such as air), dispersion of dust (into the air, forming an explosive cloud), a confined environment (such as a building or ceiling), and an ignition source (such as a spark or an open oven door). These conditions are represented in the form of a pentagon, similar to the well-known fire triangle.

According to the U.S. Chemical Safety and Hazard Investigation Board (CSB), there is general agreement in scientific literature that a dust explosion requires all five conditions simultaneously. All five were present at the facilities of West Pharmaceutical and the other company—CTA Acoustics Inc., an industrial insulation manufacturer—where the two explosions occurred.

CSB notes that the most important recommendation it can make to companies using materials that produce combustible dust is to implement the National Fire Protection Association’s (NFPA) 654 standard. NFPA 654 recommends that companies do the following to minimize the hazard:

• When designing or modifying a facility or plant, minimize surfaces where combustible dust can accumulate.

• Keep dust from accumulating and becoming airborne by frequently cleaning processing and packaging areas, including locations above production lines where dust may land.

• Minimize the dispersion of combustible dust by using dust-cleaning methods and tools that do not stir up clouds of dust.

These recommendations directly address ways to prevent the causes of explosions highlighted on the explosive-dust pentagon. West was caught off-guard by the explosion mainly because no one had noticed that dust had accumulated above a suspended ceiling, despite rigid cleaning practices in its process area, says Angela S. Blair, a chemical-incident investigator for CSB who worked on the investigations into both explosions. The other company’s employees were using dust blowers instead of dust vacuums, stirring up the hazardous dust into explosive clouds near ovens, she says.

CSB conducted investigations of both the West and CTA explosions and found several common factors in both incidents. “Both West and CTA failed to recognize the explosive potential of the dust, or to take precautions laid out in fire codes, or to train workers in the hazards of the material,” according to the CSB report. “Building design and modifications did not address the hazards of combustible dust. Material safety data sheets (MSDSs) for materials that may form combustible dusts did not adequately communicate explosion hazards.” On the West explosion, the report noted that although state occupational safety and health authorities, fire code officials, and insurance inspectors had inspected the facilities prior to the explosions, none were sufficiently aware of combustible-dust hazards to detect the problem during inspections.

The report on West contains recommendations for improving policies and procedures in facilities using these chemicals, such as:

• Revise policies and procedures for new-material safety reviews. In particular, use the most recent versions of MSDSs and other technical hazard information. Fully identify the hazardous characteristics of new materials.

• Develop and implement policies and procedures for safety reviews of engineering projects. In particular, address the hazards of individual materials and equipment and their effect on the entire processes and facilities. Consider hazards during the conceptual design phase, as well as during the engineering and construction phases. Cover all phases of the project, including those performed by outside firms. Identify and consider applicable codes and standards in the design.

• Ensure that manufacturing facilities that use combustible dust incorporate applicable safety precautions described in NFPA 654. In particular, ensure that penetrations of partitions, floors, walls, and ceilings are sealed dust-tight. Ensure that spaces inaccessible to housekeeping are sealed to prevent dust accumulation.

According to a 2004 press release West issued in response to CSB’s investigation, “West conducted a thorough safety review of all of its facilities, with a particular emphasis on the risks posed by dust. For more than a year, West has been implementing many of the steps now being recommended by the CSB.”

The report lists organizations that provide training information. Ultimately, however, it is the responsibility of material manufacturers to issue MSDSs to their customers that identify the hazards of known end-uses of the product. Employers must make people aware of the hazards of their working environment, says Blair.

Occupational Safety and Health Administration (OSHA) 29 CFR 1910.1200 requires employers to provide information to their employees about the materials they are working with. MSDSs are the form commonly adopted by companies to comply with this standard. Information contained in MSDSs should include potential health, safety, and environmental hazards, safe handling practices, and applicable regulatory information. The current OSHA regulation for MSDSs does not specifically address combustible-dust issues.

West Pharmaceuticals employed Crystal Inc.-PMC to manufacture the slurry paste that it used as an antitack agent in its rubber-manufacturing process. West specified what materials it wanted used in the paste (polyethylene). Crystal issued an MSDS with the paste. It described the paste as containing polyethylene, water, and soap, which, in paste form, is essentially benign. However, according to Blair, both West and Crystal were aware that the paste would dry out after the rubber was dipped into it. Crystal failed to note that when dried, polyethylene presents an explosion hazard, says Blair. No regulation currently requires this kind of specific wording in an MSDS.

“Material safety data sheets used by West and CTA were not sufficient,” she says.

“The product that generated the dust at issue was not accompanied by any warning of a potential dust explosion hazard. The MSDS given to West by the manufacturer said that there were no known hazards,” wrote West in the press release.

The American National Standards Institute’s (ANSI) Z400.1, “Hazardous Industrial Chemicals Material Safety Data Sheets—Preparation,” is the voluntary standard commonly used to construct an MSDS. OSHA’s Hazard Communication Standard recommends that the ANSI format be used.

Individual states can also adopt the NFPA’s standard fire codes. Additionally, after adopting the codes, states must enforce them, but states leave enforcement to local jurisdictions. “In some states, such as Indiana, that can mean enforcement of fire codes is up to the local fire inspector, who could be a volunteer,” says Blair.

Blair adds that CSB is currently conducting a survey to evaluate the effectiveness of MSDSs. The board also continues to study fire codes and regulations to evaluate what standards may require updating or may need to address more-specific hazards.

Blair emphasizes that only vacuum cleaners specifically designed to handle and contain combustible dust can and should be used to clean facilities that use or produce these hazardous chemicals. The National Electrical Manufacturers Association (NEMA) has written standards to rate control enclosures on such vacuums to address the hazards of combustible dust. NEMA 7/9 is a combination of two standards used and referenced together. NEMA 7 covers combustible vapors and NEMA 9 refers to atmospheres containing combustible dust. The standards describe control enclosures that are suitable for explosionproof environments.

Flexicon (Bethlehem, PA) manufactures bulk bag dischargers that are suitable for containing combustible dust. “The controls for [Flexicon’s] bulk bag interface are actually all pneumatically powered, which reduces the need for NEMA 7/9–rated control enclosures,” says Dave Boger, sales manager for Flexicon.

Another manufacturer of cleaning systems designed to contain hazardous dust is Scientific Dust Collectors (Alsip, IL). According to the company, “Dust collector specifications must include provisions for ignition-source control if an explosion hazard exists. This can involve using special electrical equipment, grounding of the filtering media, and spark arrestor features,” the company says.

“Spontaneous combustion is another source of ignition, caused by a chemical reaction. This is usually corrected by seeding with inert material.” The company also provides safety features in the form of pressure-release vents as a backup to preventive measures in ignition source elimination. The vents are designed to relieve increased internal pressure before it reaches damaging levels.

After the incident at West, the North Carolina Department of Labor’s division of Occupational Safety and Health issued a report on the threats posed by combustible dust. The report identified areas where the hazard of combustible and explosive dust can commonly be found. It included pharmaceutical plants.
In June 2005, CSB held a hearing with more than 20 experts in various fields including fire safety and dust hazards. Carolyn Merritt, CSB chairman, declared that chemical dust explosions in the United States are still a “serious industrial safety problem.”

Several smaller, more-contained explosions in facilities for other industries have occurred since 2003 due to combustible dust, though none were of the same caliber as West Pharmaceuticals, says Blair.

Motion Solution Incorporates Guide Screw to Replace Pneumatic System

Air can be unpredictable. And a pneumatically driven actuator in a shrink bundler can use quite a bit of air. Such an actuator literally pushes the product into the film or other packaging material. This kind of system can cause uneven motion control that results in increased setup time and maintenance. Additionally, uneven motion control can produce inconsistent product flow that causes the products to become misaligned, creating machine stoppage, and ultimately increasing downtime and decreasing profits.

In order to address these concerns occurring in its Classic series of shrink bundlers, Omega Design Corp. (Exton, PA) analyzed the potential of incorporating nonball leadscrews into its guide system. The Classic series are PLC-controlled machines designed for automatic shrink or stretch packaging of glass, plastic, or metal containers, boxes, or cartons into predetermined bundle configurations. Omega decided to use Kerk Motion Product’s (Hollis, NH) Rapid Guide Screw (RGS) 10,000 as the centerpiece of a new motion system it would design.

The Kerk RGS 10,000 is a screw-driven slide designed for high linear speed, accurate positioning, and long life, in a compact footprint. Omega’s product engineers worked with Kerk and its RGS 10,000 to incorporate a servomotor and a few additional components to create a new motion system to replace the existing pneumatic system. This reduced the company’s use of costly air as well as the occurrence of air leaks. Replacing the pneumatic system with the new actuator also means the company no longer has to stock various sensors and pneumatic parts.

The new bundler system has fewer components and requires less maintenance. The Kerk RGS is designed for high RPM and linear speeds, and Kerk offers a range of leads. This gives Omega more control over its machine’s operations. “Before it was just a continuous motion, 0–50 in. per second,” says Devendra “Win” Shendge, a product development specialist with Omega. “Now we can accelerate or decelerate the machine. This is critical, [because] when [you’re] dealing with some of the unusual shapes and heavier mass of some products; you can’t just thrust them through the machine at top speed. You can damage the machine as well as the product,” he says. Standard leads from Kerk include 0.100 in., 0.200 in., 0.500 in., and 1.00 in. travel per revolution. Speeds of more than 60 in. per second are possible. Shendge also says that in initial testing, the RGS 10,000 was generating 150 lb of force, whereas the original air cylinder only produced 80 lb of force.

With the reduced number of components and increased flexibility of the new system, changeover time between products has decreased. The machine can be programmed to adjust to various products through recipe-driven settings that are specific to each product’s handling needs. It can also accommodate a broad spectrum of product dimensions and package shapes. “We can take the feedback from this intelligent motion and use it to improve the overall operation of the machine,” Shendge adds.

The Kerk RGS includes an aluminum guide and carriage and is driven by a precision-rolled stainless-steel lead screw. The moving surfaces include Kerkite high-performance polymers running on Kerkote TFE coating. Its compact profile provides torsion stiffness and stability. The integral mounting base allows for support over the entire length if desired. The Kerk RGS also comes standard with a wear-compensating, antibacklash driven carriage.

Omega began discussing designing the motion system with Kerk just before Pack Expo International in November of 2004. They premiered the Classic shrink bundler with the Kerk pusher unit at the show. Shendge also says that Omega has received a number of requests for RGS 10,000 upgrades to existing bundlers. Multiple upgrade installations for existing users are planned in the near future. “We’re still in the evaluation phase, but I suspect that the RGS 10,000 will be standard for the Classic SL-18,” he says.

Upgrades to Omega machinery do not stop at the bundler’s pusher unit. Kerk is currently designing a new actuator that features a round shaft. According to Shendge, Omega is considering the use of these new actuators to replace the remainder of the pneumatic cylinders on the machine.

Copyright ©2005 Pharmaceutical & Medical Packaging News