Converge on Safety

A digital safety network meets safety requirements via a programmable controller and a digital network instead of relying on hard wiring from the safety sensors to conventional relay-based shutdown systems. This is a new approach toward safety system architecture that few people understand and many regulatory agencies can't seem to entirely agree upon.

Users and machine builders have, thus far, largely shunned this relatively new technology while they collectively wait for the various vendors and regulatory agencies to agree on common standards that would make digital safety networks a common accepted alternative, and not the bleeding-edge technology, product-safety lawsuit bonanza it has the current potential to be for tort lawyers.

"There is a small, but emerging market for safety buses/networks," says a recent Venture Development (www.vdc.com) study. "While there are some existing safety buses in use, this market is still nascent with several safety buses still in development."

How nascent? VDC says safety networks accounted for $7.1 million in sales worldwide, or 0.28% of the distributed/remote I/O market in 2002. It forecasts that safety networks will grow to $56.5 million, or 2% of the market by 2005.

The VDC report says Profisafe is presently the number one safety network, with 70.2% of sales in 2002. However, the report predicts its share will slip to 48.3% of the market by 2005. AS-Interface Safety at Work (AS-i) ran a distant second in 2002 at 18.7%, but climbs to 25.5% market share in 2005.

A 2001 study by ARC Advisory Group (www.arcweb.com), written by Richard Piggin, chairman of SafetyBus P Club (www.safetybus.com), identified 12 safety networks. Of those, only six showed up on the VDC radar as still being viable in 2005 (Table I): Profisafe, ASI, DNS, Ethernet Safety, SafetyBus P, and Interbus. Foundation Fieldbus Safety, which doesn't even exist yet, showed up on the VDC study in 6th place for 2005.

It is interesting to note that SafetyBus P from Pilz and a group of primarily European partners ran a strong third with 10% of the market in 2002, but was projected to slip to 3.2% of the market in 2005. "SafetyBus P was released in 1998, but has maintained fairly limited market share," says VDC. "A major reason is that products for this bus are not being developed or offered by the major controller suppliers."

Indeed, most of the various safety networks are large-vendor driven, and the more the support, the more popular the safety network. The ARC study says Profisafe was developed in Germany with funding from the German government and cooperation among three major automation vendors: Klockener-Moeller, Robert Bosch, and Siemens.

Meanwhile, AS-i has the support of a dozen vendors, including Festo, Omron, Pepperl+Fuchs, and Schneider Electric.

DeviceNet Safety, predicted to be third in 2005, was originally developed by Rockwell Automation, which passed the intellectual property rights to the Open DeviceNet Vendor Assn., where it enjoys the support of ODVA's 250+ members.

End users, especially those in North America, face something of a Catch 22 when it comes to safety networks. "End users face a conflict when wanting to apply safety networks," says Ian Verhappen, engineering associate at Syncrude Canada Ltd., Fort McMurray, Alberta. "The various standards, such as NFPA, UL, FM, ISA, IEC, are not all in harmony. And, of course, with today's litigious society, the risk of contravening a standard industry practice is one that most companies are unwilling to take." And while ISA-S84 and IEC 61511 allow facilities to self-certify, provided they have done the statistical analysis that says they meet the SIL (Safety Instrument Level) requirements, "this is a chicken-and-egg situation, says Verhappen. "You cannot gather the data you require unless you have it installed, but you can't install it to get the data." So, he adds, facilities rely on their equipment suppliers to submit their equipment for analysis and certification from groups such as T…"V, exida, HIMA, etc., to get the data required for the SIL calculation/analysis."

That seems clear enough. All an end user, or industrial machine builder has to do is buy an approved safety network that meets all the regulations, right? Sorry, that may not work either, says Paul Wiancko, Professional Engineer with P.R.T. Wiancko & Associates of London, Ontario. "Many equipment safety standards do not yet address safety networks and, until this happens, there will be some reluctance to use and approve them," he explains.