What Is Rotational Motion and Its Role in Concussions?

Understanding rotational motion can better protect workers from head injuries and long-term risks.

• By Sofia Hedenstierna
• Jun 01, 2023

Although we’re living in the twenty-first century, there are still many dangers in our workplaces. For certain industries, such as the construction, manufacturing and industrial industries, the risks on the job are greater than others. Due to the nature of the work, there are numerous activities that expose these workers to hazards. 

Worker safety is at a critical juncture: Between 2003 and 2010, a total of 2,210 construction workers died of a traumatic brain injury (TBI). These deaths represented 25 percent of all construction fatalities, an industry that sees higher numbers of both fatal and non-fatal traumatic brain injuries than any others.

What’s Causing Traumatic Brain Injuries?

In the construction industry, the leading causes of traumatic brain injuries are coming into contact with objects and equipment, and for fatal injuries are slips, trips and falls. One reason such accidents can lead to TBIs is that when an object glances the head or the head impacts the ground in connection with a fall, this typically occurs at an angle, which may expose the head to rotational motion. 

Understanding Rotational Motion

Rotational motion can be described as a combination of rotational forces (angular acceleration) and rotational energy (angular velocity), which may result from oblique impacts to the head. When rotational motion is transferred to the brain, it begins to rotate. If the rotation is large enough, this can lead to shearing of the brain’s axons, the cable transmitters of neurons.

Both linear and rotational motion can occur and cause injury during most impacts. Yet different kinds of injuries can potentially be caused by these different types of motions. For example, linear motions can primarily lead to focal injuries, including contusions and fractions. Rotational motion, on the other hand, may cause diffuse injuries, such as subdural hematoma and diffuse axonal injury. Furthermore, experiments and numerical computer simulations have demonstrated that the brain is more sensitive to rotational motion than linear motion in regard to concussions. Essentially, this means concussions caused by rotational motion occur at lower levels of energy than in cases involving linear motion. In other words, even impacts that may seem to be light can lead to concussions when rotation is a factor.

Understanding How to Protect Yourself

OSHA mandates that hard hats and head protection be worn by workers who are at risk for head injuries, but there are still many risks on construction sites that standard helmets don’t always account for. 

The first step is to wear a helmet and make sure that it fits both securely and comfortably on your head. Additionally, helmets equipped with rotational motion mitigation systems can be considered. Thanks to many years of research into rotational motion, additional safety can be added to helmets to potentially help mitigate its impact. For instance, several rotational motion mitigation systems enable material in the helmet to slide and move relative to the wearer’s head. The intended outcome is to redirect rotational energy to linear energy, and consequently help reduce the amount of rotational energy that could otherwise be transferred to the brain. 

What To Know About Today’s Helmets

Helmets have historically been designed to protect the wearer from linear forces. As is reflected in today’s regulatory standards, most helmets today work to protect wearers against a linear impact to the crown. For example, five performance tests must be met to assign safety helmets their classification according to the standard ANSI/ISEA Z89.1. These include impact energy attenuation, force transmission, flammability, apex penetration and electrical insulation. 

Force transmission tests determine whether a helmet is able to reduce the force of a linear impact from a falling object to the crown of the wearer’s head. This serves as a clear reminder of the need to wear helmets on the job. The additional impact energy attenuation test, which is required for an ANSI Z89.1 type 2 helmet assignment, tests a larger protective area of the helmet with impacts on the side, front and rear of the helmet. However, it still only analyzes the linear accelerations and doesn’t test for the rotational motions that could be transmitted to the head. 

What is noticeably missing in the current standards’ regulations is testing for angled impacts to the head. Angled or off-center impacts are one of the most common accident scenarios and have a proven ability to cause brain injuries. However, today’s regulatory standards do not certify helmets based on their capability to assist in mitigating against rotational motion from an off-center or angled impact. 

It is encouraging to see that test standards in the moto and sports sectors are beginning to introduce the testing of angled impacts. This underscores the importance of both considering rotational motion and what a dangerous effect it can have on one’s head in the safety sector.

Why the Construction Industry Must Care

In the construction industry, the majority of TBIs that take place are not caused by an accident that occurs just as helmets are tested for, such as a pure linear impact to the crown of the safety helmet. Real life accidents, whether it be a falling object glancing the side of someone’s head or a fall, typically result in workers’ striking the safety helmet from an angle. On a job site, if someone were to slip and fall, they would most likely hit their head at an angle, which can lead to rotational motion. 

In order to keep workers safe, it is imperative that the potential causes of TBIs, including rotational motion, be addressed and receive greater awareness from those at risk. A survey from PPE provider J.J. Keller Safegear reported that the top reasons why employees did not wear their PPE were because they didn’t want to (72 percent) or they thought it wasn’t necessary (50 percent). Increased education around the risks of rotational motion, and common accidents on the job, will help workers understand the true risks of TBIs and increase PPE usage. 

The type of helmet that workers wear is almost as important as ensuring they are worn in the first place. Workers should guarantee that their helmets meet current safety standards. Additionally, they could consider helmets equipped with a rotational mitigating system, which is designed to help reduce the transmission of rotational motion to the wearer’s head in the case of certain angled impacts. 

There are a number of risks that workers face on the job, many of which aren’t expected to go away anytime soon. Therefore, education about rotational motion and TBIs and implementing best practices for safety measures and PPE usage is urgently needed to improve workplace safety. 

This article originally appeared in the June 1, 2023 issue of Occupational Health & Safety.