How to Assess Machine Risks

Tolerable risk is a concept recognized in the ANSI B11.TR3-2000 technical report, which is useful in the assessment process.

THERE'S been a change in the motivation of the companies that call STI Machine Services, Inc. seeking help with their machine guarding concerns. The change is that most of them haven't been stampeded into action by an OSHA citation or a crippling injury.

"Traditionally, it used to be that we would only get called in after an accident or a near miss occurred," said Chris Soranno, a machine & process safety engineer and assessment & proposal coordinator for STI Machine Services, Inc. in Cleveland, Ohio. "What we're starting to see now is people trying to be more proactive, as opposed to reactive. We have companies calling up because they want to prevent the injuries from happening to begin with," he said during a recent interview.

A call from a large company might have been prompted by its acquisition of new facilities or new operations, Soranno said. The newly acquired unit then must meet the parent company's corporate standard, which may include doing a risk assessment, reducing risk, and bringing the equipment to a tolerable level of risk. "Other facilities, they've just had a new piece of equipment coming in," he said. "For some of those, finally the light bulb's turned on and they realized they need to do something. There's no new equipment, nothing's really changed. They finally decided to build it into their budget to safeguard, and that's going to be a priority from that point forward."

Soranno conducts on-site machinery risk assessments. He said he's found it is usually the machine operators, not the managers, who will underestimate a machine's risk level. Veteran operators frequently tell him they've never been hurt on their machines, so they conclude the machines aren't risky. He tells the operators this doesn't mean the machines aren't risky; it means they've been lucky. "That mindset is the hardest to overcome," he said. "You explain to them: 'Yes, you haven't had an accident yet, but it doesn't mean it couldn't happen.' "

Conducting a Risk Assessment
When STI Machine Services does an assessment, a photograph won't suffice. Its personnel need to see the machinery in use. "We try to gather as much information as possible while on site to complete the documentation and then get right to the risk reduction part, because that's what everyone's really concerned about," Soranno said.

The assessors look at the worst-case hazard for that machinery, calculate a risk score, and then recommend some type of risk reduction. Assessing a small machine may cost only $150 to $200. Assessing a full-scale processing line such as a robotic welding line costs about $1,000 per day on site, he said.

The risk scale STI Machine Services uses is based on EN 1050, the European machine safety standard; ANSI/RIA R15.06-1999, American National Standard for Industrial Robots and Robot Systems--Safety Requirements; and ANSI B11.TR3-2000, Risk Assessment and Risk Reduction--A Guide to Estimate, Evaluate and Reduce Risks Associated with Machine Tools. The latter is a technical report (available from The Association For Manufacturing Technology's Web site, www.mfgtech.org) that is part of the B11 series written for the machine tool industry. The series addresses hazard control for specific machine types.

Tolerable risk is a concept recognized in the TR3 technical report, which describes a hierarchy of four levels of safeguarding that can be applied, depending on the level of risk reduction needed for that machine. "Zero risk is really unattainable," Soranno explained." Anything you do, there's risk involved."

The STI scale assigns points that are based on three factors. A machine that scores in the 0-6 range is considered low risk; scoring 7-11 represents medium risk; 12 and above is a high-risk application. The three factors and their potential points are:

  1. Severity of potential injury: The most severe risk has the potential for fatality (10 points). Next comes major (6 points); serious, such as a burn or broken bone from which the victim can return to work (3 points); and finally minor, for cases that require first aid or less (1 point).
  2. Frequency of exposure: If someone is exposed to the risk several times per day, that is scored as frequent (4 points). A daily exposure is scored as occasional (2 points). If weekly or less frequent, it's scored as seldom (1 point).
  3. Probability of injury: The highest level here is certain (6 points), followed by probable (4 points), possible (2 points), and unlikely (1 point).

The assessor adds those and considers other factors, as well. If more than one person is exposed to the hazard, the assessor multiplies the number of people by the severity factor. If a person spends more than 15 minutes per access in the danger zone without lockout/tagout protection, the assessor adds 1 point to the frequency factor. If the operator is unskilled or untrained, 2 points are added to the total.

"Based on this system, we're going to get some risk score," Soranno said. "So if you have a number of people involved in a potentially fatal hazard, you could have a risk score of 40 or 50, or above. There really is no maximum number. Anything 12 or above is going to be a high risk. From that, we try to design a safeguarding solution commensurate with the risk level."


"[Machine guarding] is an investment--not just an expense, but an investment in the equipment and the machinery, as well as the employees, to keep the facility up and running as it should."

Employers typically do a wall-to-wall assessment of machinery in their entire plant or a specific department, then prioritize a plan of attack based on the risk scores. "We have a lot of facilities that, in the next year, want to safeguard all the high-risk machines. In the following year, all the medium-risk machines. And in the two years after that, they'll finish up all the low-risk machines," he said.

Machinery isn't idle while this work goes on. As Soranno explained it, OSHA doesn't expect a full shutdown but does expect an employer to have a plan in place and to install supplementary guarding in the meantime, until a final solution is implemented.

Where Some Employers Go Wrong
Soranno recommends a 12-step process to carry out effective machine guarding. It starts with identifying applications to address and reviewing injury history. The final step is close-out and sign-off. Companies tend to go wrong in a few places along the way, he said.

For one, end users often don't appreciate that their specific use of a machine is what these professionals need to see. "Everybody thinks there's just a cookie-cutter answer to safeguard every type of machine. But it really is fairly custom [and] based on how they're actually using the equipment."

Also, end users may not accurately perceive the cost of the control systems they need, he said. To safeguard high-risk applications, you need control reliable circuits, which include dual channel circuitry with monitoring for the electrical, hydraulic, and pneumatic control systems. If the end user doesn't have someone who understands this requirement, Soranno said, it won't get what it needs.

Assessors frequently see companies do an installation without following all of the best practice approaches they should. "Like physical barriers: A fence is a pretty simple concept to build and install," he said. "But it has to be far enough away, based on how big the opening for the material is. So if you're using a mesh with, say, a 2-inch opening, there's a requirement that that has to be so many inches away so the person can't stick their finger or their hand through the opening to reach that hazard." Then there are requirements for the guard's height that are based on the location of the hazard. Maintenance people frequently aren't aware of these requirements and may install the safeguarding equipment incorrectly. They're great at many things, at keeping machines up and running, but to rely on them to know all of the standards applying to each piece of equipment and to design and install control systems is too much to expect, said Soranno, who recommends instead finding a competent outside professional who specializes in machine safeguarding.

"What we really strive for is a balance between safety and productivity," he said. "If the machine's not productive, the first thing they're going to do is bypass the safeguards. But at the same time, you need the safeguards to make sure that they're operating safely and still can produce the parts they're intended for."

Machine guarding can be particularly challenging for small businesses, which may not want to or be able to invest in machine guarding software or a library of standards to help their managers assess and mitigate risks. "Sometimes they underestimate the importance of the safeguarding, don't really budget what's necessary to get it done correctly," said Soranno, "whereas usually with larger corporations, you have a whole staff of safety personnel who have been down this path before with other companies. They heighten the awareness and the importance of it, so they've worked it into the corporate mindset that it is an investment--not just an expense, but an investment in the equipment and the machinery, as well as the employees, to keep the facility up and running as it should."

This article appeared in the August 2006 issue of Occupational Health & Safety.

This article originally appeared in the August 2006 issue of Occupational Health & Safety.

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