NEW WORLDWIDE SAFETY standards and domestic technical reports lean on the principle of performance-based safety control solutions. The Europeans felt trade economic pressures before we did, and knew they would have to prevent trade barriers through a universal standards strategy. This opened up a new approach to safety measures, one that looks at the evaluated risk of an unmitigated machine as the design basis for additional safety measures, albeit a safety system or other protective layer. Machine builders who follow this approach can design a safer machine and, in the long run, lower end user lifecycle costs. Other significant benefits surface as well as a result of this proactive engineering and management process.
The main benefits resulting from a performance-based, machine safety lifecycle approach include:
- A closer pre-sales relationship with the potential user
- Proper front-end selection of protection devices
- A decrease in specification errors and resulting accidents
- Consequences, impacts on manufacturing, and corporate image losses can be quantified (beyond basic personnel safety and equipment costs) and included for a higher justification
- The production process is enhanced by uncovering embedded reliability issues
- Lower compliance costs for machine use abroad as a result of uniform methods
Details on each of the above will follow, but first here is a quick review of new and historical methodologies from both the machine builder and end user perspectives.
A Brief History of Safety Control
As mentioned, the U.S. does not have a unified front that clearly spells out each machine builder's and end user's machine safety requirements. Unfortunately, the general attitude is that the end user has ultimate responsibility for an incident. So, unless the end user clearly specifies his machine safety needs, it is left to the machine builder--who is under pressure to maintain costs in a competitive environment--to interpret current laws and standards to determine whether or not the system is in compliance.
This is not an easy task because the regulation and standards trail is murky at best. Figure 1 (click the Download Now button at the end of this article for a pdf version of all figures mentioned in this story) shows the compliance maze that a unique automated machine builder must follow. OSHA, naturally, is the overriding regulator and provides very general "1910.2xx" standards. The figure also references the American National Standards Institute (ANSI) for application standards and the Nationally Recognized Testing Laboratories (NRTLs) for device standards and certifications. ANSI, in turn, oversees the development of needed standards through various consensus bodies including the Association for Mechanical Technology (AMT) and the National Fire Protection Agency (NFPA), to name a few. There might be reference and industry-specific standards that should be reviewed as well.
New Assessment-Based Approach
Rather than just following a prescriptive approach to standard machine tool applications or following "good engineering judgment" for unique apparatus, the new ANSI (B11.TR3 (Dec. 2000), B11.TR4, RIA 15.06, and B11.20) application standards all point to a risk-based, performance-oriented procedure. Some machine builders may feel unsettled by this, because no longer does someone tell them what they should do so that they can stand behind it. An appropriate analogy is that of a mother who protects her child against the winter elements. A mother wants to protect her child, so she tells him he must wear a coat to remain warm. If the government felt this mother represented the norm and wanted all children to be protected, then they would state that all children must wear coats.
But what about the season? (Production and resulting personnel hazard exposure rates fluctuate too.) What if the child already has on two or three layers of clothing? (How many protective layers does your application have?)
Even if the weather stayed cold all the time, are there different temperature levels that require different coats (like different machine safety control integrity levels)? Based on the degree of cold, what would the consequences be? Is the child in good health and might just catch a cold as in most cases, or could he come down with a severe case of pneumonia and die? (Likewise, what is the magnitude of unmitigated consequences with your machine?)
These new standards weigh the risk of each hazard, compare it to a tolerable level that is based upon existing protection levels, and if insufficient, add more protection. The gap itself will determine the appropriate functionality and integrity of the preventative measure. This can be accomplished by using a risk matrix table (Figure 2 -- click the Download Now button at the end of this article for a pdf version of all figures mentioned in this story) ), which has the likelihood and consequence metrics across two axes. Quadrants are internal to the matrix, and should be calibrated to the different approaches to risk reduction and protection technology that the company wants to standardize on.
Bank on the Benefits
Lets take a closer look at the benefits mentioned earlier.
Benefit 1--Closer pre-sales relationships are developed. For the machine builder, this means that he will review with the prospective user his list of known hazards for his equipment and relay how he lowered the risk to a tolerable level. The user can evaluate the hazards presented, add any additional hazards that might result from the equipments location at his site, and ultimately determine if he agrees with the machine builders evaluation. If the user needs more protection, he might elect to have the machine builder upgrade the control reliability solution to a level that matches the perceived risk.