Machine Guarding 101- A Forensic Expert Overview Expert Article

The experts at Robson Forensic investigate many industrial mishaps to understand how they occurred and who is liable. The results of these incidents are gruesome, sometimes deadly, and often preventable. Through the course of their training, education, and experience, our engineers and industrial safety experts have developed expertise in machine guarding and the relevant workplace safety standards.

While machine guarding and design is second-nature to many of our technical experts, we understand that most of our clients have not undergone any formal training on the topic. This article is intended to provide a 101 style overview of machine guarding, including the common hazards and relevant standards. 

Machine Guarding Expert Witness

Machine Guarding 101

The purpose of a guard is to protect people from hazards associated with machinery. Guards also protect people from injuries that occur due to fatigue, distraction, and other forms of human failure. The illustrations below depict various hazards that may be encountered in industry.

Inrunning Nip Hazards

Inrunning Nip Hazard Expert Witness

An inrunning nip point is created by a mechanism having one or more rotating parts. Wherever parts rotate over, under, or near a stationary object, or wherever machine parts rotate in contact with or near other rotating parts (in opposing directions) an inrunning nip is formed. The danger of the inrunning nip hazard is that it draws objects into the mechanism, entrapping, and often flattening them. It can be difficult, if not impossible, to withdraw entrapped body parts from these hazards.

Shear Hazards

Shear Hazard Expert Witness

A shear hazard is created where two machine parts move across each other or move closely enough to cut or move an object that enters the system. Shear hazards frequently exist in machinery and equipment designed for cutting or punching.

Crush Hazards (Pinch Point hazard)

Crush Hazard Expert witness

A crush hazard is created where two objects move toward each other or when a moving object approaches a stationary object. Injuries occur where body parts get caught or crushed between two parts/objects. Crush hazards frequently exist in machinery or equipment designed to bend, stamp, or form metals.

Snag Hazards

Snag Hazard Examples

A snag hazard is created where rotating or reciprocating equipment includes protrusions that can catch or snag on clothing or other passing objects. Snag hazards have the potential to quickly draw a person into moving equipment, creating entanglement hazards. They can also tear flesh or dismember body parts depending on their size, shape, and sharpness. While projections on rotating shafts can catch or snag clothing, a bare rotating shaft can present a snag hazard as well.

Industrial Machine Safety

Manufacturers must assure that hazards are engineered out of the product during the design process. If a hazard is inherent and cannot be designed out of the machine, system, or process, the hazard must be guarded. In all cases, the user must be warned or instructed about dangers of the product. These steps form the fundamental principles and rules of practice for the safe and appropriate engineering of products, and are sometimes referred to as the hierarchy of hazard control.

Machine Guarding Safety Hierarchy Expert Witness

The requirement for guarding and, more broadly, machine safety is reinforced by a number of government and industry oversight organizations. In the section below we highlight some of the most commonly cited references on machine guarding.

Robson Forensic possesses an extensive technical library that houses standards and reference materials dating throughout the modern industrial era. In many forensic investigations, our experts are able to reference industry specific resources to establish the relevant standard of care at the time that a piece of machinery or equipment was designed, built, or modified.

OSHA Requires Guards:

1910.212 Machinery and Machine Guarding

Title: General requirements for all machines

1910.212(a)(1) Types of guarding. One or more methods of machine guarding shall be provided to protect the operator and other employees in the machine area from hazards such as those created by point of operation, ingoing nip points, rotating parts, flying chips and sparks. Examples of guarding methods are - barrier guards, interlocked guards, two-hand tripping devices, electronic safety devices, etc.

National Consensus Standards Require Guards

National consensus standards, such as those promulgated by Underwriters Laboratories, require adequate guarding against hazards.

UL 73 Standard for Safety, Motor-Operated Appliances.

Protection against Casualty Hazards

19. General

19.1 If the operation and maintenance of an appliance by the user involves casualty hazard, suitable protection shall be provided to minimize the hazard.

19.1A In applying the requirement of paragraph 19.1 consideration should be given to reasonably foreseeable misuse of the appliance.

19.2 The adequacy of a guard, a safety release, an interlock, etc. and whether such a device is required are to be determined from an investigation of the complete appliance, its operating characteristics and the likelihood of a hazard resulting from a cause other than gross negligence.

19G. Enclosures and guards

19G.1 A hazardous moving part shall be enclosed. See paragraph 19G.2.

19G.2 Among the factors to be considered in judging the acceptability of an exposed moving part are (1) the degree of exposure necessary to perform the intended function, (2) the sharpness of the moving part, (3) the likelihood of unintentional contact therewith, (4) the speed of the moving part, and (5) the likelihood that a part of the body or clothing would be endangered by the moving part. These factors are to be considered with respect to both intended operation of the appliance and reasonably foreseeable misuse.

Industry Guidelines Exist as Well:

The National Safety Council advises as follows with respect to guards:

Acceptable guard requirements

A guard should:

  1. Conform to the standards of the ASA or the state inspection department having jurisdiction.
  2. Be considered a permanent part of the machine or equipment.
  3. Afford maximum positive protection.
  4. Prevent access to the danger zone during operation.
  5. Not weaken the structure of the machine.
  6. Be convenient; it must not interfere with efficient operation of the machine nor cause discomfort to the operator.
  7. Be designed for the specific job and specific machine, with provisions made for oiling, inspection, adjusting, and repairing of the machine parts.
  8. Be durable, resistant to fire and corrosion, and easily repaired.
  9. Be constructed strongly enough to resist normal wear and shock, and to withstand long use with minimum maintenance. It should not, itself, present hazards such as splinters, pinch points, shear points, sharp corners, rough edges, or other sources of injury.
  10. If possible, a guard covering rotating parts should be interlocked with the machine itself so that the machine cannot be operated unless the guard is in place.

Machine Guarding Expert Witness Investigations

The industrial safety experts at Robson Forensic have designed, built, maintained, and operated a broad variety of industrial machinery. Moreover, our experts have investigated countless mishaps over the years involving all manner of equipment. By retaining Robson Forensic, you are securing the full weight of our collective experience, knowledge, and resources toward the resolution of your case.

To discuss your case with an expert submit an inquiry.

Featured Expert

Harold Ehrlich, Industrial Engineer & Product Design Expert

Harold Ehrlich

Industrial Engineer & Product Design Expert
Harry has worked as an Industrial Engineer since 1978. He has held positions of increasing responsibility within industry and has been responsible for the design and manufacture of consumer products,… read more.


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