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:
Speed of approach of the individual
Total response time of the safeguarding device as stated by the supplier
Response time of the interface
Response time of the control system
Time it takes the machine to stop hazardous motion; and
Depth penetration factor of the safeguarding device.”
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.
Forensic engineers may be called upon to investigate a broad array of problems concerning a machine. Cases involving physical injuries and even death are a large part of what we investigate in order to determine what caused the accident to happen and who may be at fault. Occasionally, problems with a recently designed custom machine do not cause a physical injury, but instead cause a “financial” injury. This type of “injury” can negatively impact the machine designer, the machine purchaser, or possibly both. Financial injuries can be quite substantial, just as physical injuries can be, and may severely impact a company’s cash flow which can make or break a company. A refusal to pay a designer/builder of a machine or paying for a machine that ends up not meeting the agreed upon performance specifications can have catastrophic consequences for many businesses, especially for small ones. 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
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
LIVE WEBINAR: “Property Claims Issues at Manufacturing Facilities” | Presented by WARREN’s President and Senior Consulting Engineer, Jennifer Morningstar, P.E., CFEI.
COURSE LEARNING OBJECTIVES
The learning objectives of this course are to provide the attendees with information on the four major facets of property claims that are commonplace in manufacturing facilities.
They are:
Subrogation against third parties;
Boiler & machinery vs property claims;
Scope of loss, and
Business interruption
Each facet will be explored and exemplified by at least one case study.
Hail property damage is frequently reported after an HVAC service call. Building owners are often unaware there is damage until the power bill starts trending higher and the HVAC system is simply not cooling effectively. Take look at the fins! The National Weather Service reported over $722 million in property damage from hail in 2018. Based on NWS data, hail caused more property damage than tornadoes or thunderstorms. Only Tropical Storms/Hurricanes at $12 billion, coastal storms at $1 billion and flooding at $1 billion were more costly than hail to property.
One of the items very susceptible to damage is the HVAC system. The heat that is removed from the interior of a building must be rejected to the environment. As such the HVAC system is placed where it can have unhindered access to outdoor air in order to function properly. This often results in the unit being placed in a large open space such as a rooftop, making it susceptible to damage such as hail. Read More
The Occupational Health and Safety Administration (OSHA) “Top 10 for 2018” violations once again have Machine Safeguarding earning a position on the list. Machine safeguarding was the 9th most cited standard as noted in the list below:
A worker was injured while testing gas springs similar to the type that hold the hatchback of an SUV open. The hazard that injured the worker was an unguarded shear point. The tester contained a mounting plate that was raised and lowered by a pneumatic cylinder.
The pneumatic cylinder lowered the mounting plate while the worker’s fingers were in the hazardous, unguarded shear point. Read More
Equipment and appliances supplied with fuel gases like natural gas, propane and butane are a common and convenient part of most of our lives. Such devices as gas grills and ranges, ovens, furnaces, space heaters and water heaters usually perform without incident. However, when they malfunction the potential for incidents such as fires and explosions, carbon monoxide (CO) poisoning and burn injuries may occur. These incidents may be due to design and manufacturing defects in the product, or improper installation or operation of the device.
I recently worked on an interesting case involving a box baler. An employee of a butcher shop put some empty cardboard boxes in a vertical box baler and pushed the control switch to compact the boxes. After the 30 by 60 inch platen weighing 851 pounds returned to its raised position, the employee reached into the open space above the bottom door on the baler and began to clear cardboard from the bale tie slots in the bottom of the raised platen. Suddenly, and without warning, the steel pin attaching the platen to the raised hydraulic cylinder rod failed. The heavy steel platen fell and crushed his arm which was outstretched over the baler door into the compaction space.
