Hazard can be defined as a potential source of harm. Machine safeguarding seeks to protect people from these potential sources of harm. Often distance from a hazard will play a key role in providing a means of protection.
One would often think of distance as it relates to the location of a barrier guard from a hazard. ANSI B11.19, Performance Criteria for Safeguarding, defines safety distance as “the distance a safeguard is installed from a hazard such that individuals are not exposed to a hazard.” An example from ANSI B11.19 of the recommended distance of a slotted opening in a barrier guard from a hazard is shown in the table below:
Table 1: Minimum Slotted Opening vs Distance from Hazard – From ANSI B11.19
This information will help assess if the opening present in a barrier guard will meet the values established in a consensus standard such as ANSI B11.19. These distances and dimensions should be carefully considered when designing fixed barrier guards.
However, when more sophisticated means such as safeguarding devices are used to protect an individual from a hazard, distance takes on a different meaning. ANSI B11.19 defines a safeguarding device as “a device that detects or prevents inadvertent access to a hazard.”
A light curtain is a well-known presence-sensing device. ANSI B11.19 defines a presence sensing device as “a device that creates a sensing field, area or plane to detect the presence of an individual or an object.” An example of a light curtain is shown below.
If the individual utilizing a machine protected by the light curtain breaks the plane created by the sensing device, then the hazard behind must be rendered safe before it can be reached. For example, a hazardous motion must stop to prevent an injury to the individual that breaks the plane. Here the distances noted in Figure 1 above may not be applicable and a different method of determining the safety distance should be considered.
ANSI B11.19 states in section 6 General safeguarding requirements, 6.3 Safety distance:
“When required by this standard, the guard or safeguarding device shall be located a distance from its associated hazard such that individuals cannot reach the hazard before cessation of hazardous motion (or situation).”
Here we see that the hazard must be rendered safe before an individual can reach it through the presence sensing device and be injured.
Furthermore, section 8 Safeguarding devices, 8.3 Electro-optical, RF and area scanning presence-sensing safeguarding devices, 8.3.2.3 states:
“The presence sensing device shall be installed at a location so that the effective sensing field prevents individuals from reaching the hazard(s) during the hazardous portion of the machine cycle.
How do we determine this location or “safety distance”? Explanatory information in ANSI B11.19 notes:
“The safety distance calculation is dependent upon the:
Here we see that with a presence sensing device, the value for a safe distance has many facets that must be considered to provide for safe operation by a user. ANSI B11.19, Annex D provides a method for determining what a safe distance should be based on factors mentioned above.
Safeguarding is often not a one size fits all activity. Careful consideration should be given to the safeguarding method chosen and proper attention paid to the specific design details. Careful selection and proper design details will lead to a safer machine.
Chad Jones, PE, CFEI, CVFI, CMSE has a Bachelor of Science in Mechanical Engineering from Clemson University. Chad has over 25 years of engineering experience including mechanical, process, and manufacturing engineering. This work has included equipment design, machine safeguarding, cost estimating and safety compliance. Chad also has over 10 years of commercial, industrial, and residential HVAC and plumbing design experience. A lifelong auto and motorcycle enthusiast, Chad is accomplished in the maintenance, repair, and modification of vehicles and engines. Chad is a Certified Fire and Explosion Investigator, Certified Vehicle Fire Investigator, and IFSAC certified Firefighter II in Greenwood County, South Carolina.
As the holiday season nears, thoughts turn to wonderful home-cooked meals with family. Few things in life are more pleasurable than a traditional holiday turkey feast. Yet for an unfortunate few, holiday meal time can turn tragic if a turkey frying accident occurs. While fried turkeys may be tasty, many fire safety experts feel that the reward is not worth the risk. Read More
Machine guards can be compared to the clothes we wear every day. Indeed, they serve a very important purpose. Imagine someone leaving their home on a fine, sunny morning wearing nothing but a smile. Wonder how far they will get through the day before things start going poorly for this individual?
There will be more than a few raised eyebrows and blushes when he stops into the local Starbucks for his usual morning double-dipped and whipped, chocolaty chip with a touch of pumpkin spice cappuccino fix. Good luck with that! Probably going to leave disappointed, empty-handed, and likely wearing handcuffs. This will be the beginning of a very long, very bad day for that individual. Had he recognized the risks associated with this type of behavior, and then put forth a little effort to cover up, he would have prevented many unfavorable and possibly life-changing personal and legal problems from ever occurring!
And so it is with properly guarding a machine. Machine safeguarding helps to protect workers from preventable injuries. Read More
Please join us in welcoming Mechanical Engineer Bob Hickman, P.E., to the WARREN family! Bob has over 30 years of manufacturing and machine design experience in production and quality-driven environments. Bob holds a Bachelor of Science in Mechanical Engineering from Clemson University.
Bob’s Areas of Expertise Include:
-Machine Safeguarding
-Machine Design
-Equipment Failure
-Mechanical Engineering
-Industrial Accident Investigation
-Codes & Standards
-Machinery & Equipment Damage Assessment
-Products Liability Read More
Hazard, risk, and harm are terms that are used in the world of machine safeguarding. How do these words shape the concept of machine safeguarding? Let’s look a little deeper….
Hazard, which Merriam-Webster defines as a noun, lists its first meaning as a source of danger.
1: a source of danger
2a: the effect of unpredictable and unanalyzable forces in determining events : CHANCE, RISK
This is the second in a two-part blog series about conveying equipment that severely injured a worker at a mine. In case you missed it, click here to read Part 1 where I describe the incident and the mining equipment. In this part, I will discuss my engineering analysis of the incident and the machinery involved and share the conclusions I reached.
The injured miner was a front-end loader operator. He was not a maintenance worker. He simply responded to a radio request for help with the conveyor. Power to the electric conveyor motors was locked out, but none of the maintenance workers did anything to lock out or block the hazardous gravitational potential energy in the heavy load of stone on the belt. Read More
This is the first of a two-part blog series describing an incident involving conveying machinery that seriously injured a miner. Part 1 describes the machinery and the incident. In Part 2 I will summarize my engineering analysis of the incident and share the conclusions I reached.
A loaded, inclined conveyor belt may contain hazardous levels of energy due to gravity. To protect workers, anti-reverse devices called backstops are installed on inclined conveyors to prevent unexpected downhill movement. The Conveyor Equipment Manufacturer’s Association (CEMA) defines a backstop as: Read More
Two little letters, CE. Perhaps you have seen those two letters on a machine nameplate or some other equipment. What is the meaning behind those two stylized letters and how does it drive the design of safer machinery? Let’s take a closer look. Read More
The thirty-thousand-foot view of manufacturing is raw material in, alter in an appropriate fashion, finished product out, by-product out. Since the finished product keeps a business in business, it gets the most attention. What about by-products or waste streams? Read More
A mini-excavator at a job site developed a leak at a hydraulic fitting at the base of the cylinder that raises and lowers the boom. A subcontractor foreman at the site raised the boom to search for the leak. The foreman found and attempted to tighten the leaking fitting. When he did, the fitting separated from the base of the cylinder, releasing the hydraulic pressure that held the boom aloft. The boom fell and the bucket struck a nearby superintendent for the general contractor.
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