Manual handling of loads (MHL) or manual material handling (MMH) involves the use of the human body to lift, lower, carry or transfer loads. The average person is exposed to manual lifting of loads in the work place, in recreational atmospheres, and even in the home. To properly protect one from injuring themselves, it can help to understand general body mechanics.
Hazards and injuries
Manual handling of materials can be found in any workplace from offices to heavy industrial and manufacturing facilities. Often times, manual material handling entails tasks such as lifting, climbing, pushing, pulling, and pivoting, all of which pose the risk of injury to the back and other skeletal systems which can often lead to musculoskeletal disorders (MSDs). Musculoskeletal disorders can be defined as often involving strains and sprains to the lower back, shoulders, and upper limbs. According to a U.S. Department of Labor study published in 1990, back injuries accounted for approximately 20% of all injuries in the workplace which accounted for almost 25% of the total workers compensation payouts.
To better understand the potential injuries of manual handling of materials, we must first understand the underlying conditions which can cause the injuries. When an injury occurs from manual handling of materials, it often is a result of one of the following underlying condition(s). Awkward posture: Bending or twisting Repetitive motions: Frequency of a task Forceful exertions: Carrying or lifting heavy loads Pressure points: The load applying pressure to select areas on the body only Static postures: Staying in the same position for extended periods of time
Although musculoskeletal disorder can develop over time, when manual handling of materials, they can also occur after only one activity. Some of the common injuries associated with manual handling of loads include but are not limited to: Sprains and strains of muscles, ligaments, and tendons Back injuries Bone injuries Nerve injuries Tissue injuries Acute and chronic pain
In addition to the injuries listed above, the worker can be exposed to soreness, bruises, cuts, punctures and crushing. It can be helpful to think that health comes first, and that one's health is something temporary that must be taken care of.
Commonly affected industries and workforces
Although employees can be exposed to manual handling of materials in any industry or workplace there are workplaces that are more susceptible to hazards of manual material handling. These industries include but are not limited to: Warehousing Manufacturing facilities Factories Construction sites Hospitals Nursing home and retirement facilities Emergency services (fire, medical, police) Farms/ranches
Evaluation or assessment tools There are multiple tools which can be used to assess the manual handling of material. Some of the most common methods are discussed below in no particular order.
NIOSH lifting equation The U.S. National Institute for Occupational Safety and Health (NIOSH) is a division of the Centers for Disease Control and Prevention (CDC) under the United States Department of Health and Human Services. NIOSH first published the NIOSH lifting equation in 1991 and went into effect July 1994. NIOSH made changes to the NIOSH lifting equation manual in 2021 which included updated graphics and tables and identified errors were corrected.
The NIOSH lifting equation is a tool (now application ) that can be used by health and safety professionals to assess employees who are exposed to manual lifting or handling of materials. The NIOSH lifting equation is a mathematical calculation which calculates the Recommended Weight Limit (RWL) using a series of tables, variables, and constants. The equation for the NIOSH lifting equation is shown below
where: LC is a load constant of 23 kg (~51 lb) HM is the horizontal multiplier VM is the vertical multiplier DM is the distance multiplier AM is the asymmetric multiplier FM is the frequency multiplier CM is the coupling multiplier
Using the RWL, you can also find the lifting index (LI) using the following equation:
The lifting index can be used to identify the stresses that each lift will expose the employees. The general understanding is that as the LI increased, the higher risk the worker is exposed to. As the LI decreases, the worker is less likely to develop back related injuries. Ideally, any lifting tasks should have a lifting index of 1.0 or less.
The NIOSH lifting Equation does have some limitations which include: Only using one hand for lifting/lowering Lifting or lowering for over 8 hours Lifting or lowering while in the seated or kneeling position Lifting or lowering in restricted areas (where full range of motion cannot be achieved Lifting or lowering unstable objects Lifting or lowering while carrying, pushing, or pulling. Lifting or lowering using devices such as wheelbarrows or shovels Lifting or lowering with high speed motion Lifting or lowering on unstable floors Lifting or lowering in extreme heat, cold, or humidity.
The NIOSH Revised Lifting Equation Manual can be found on the CDC's website or by clicking here.
Liberty Mutual tables Liberty Mutual Insurance has studied tasks related to manual materials handling, resulting in a comprehensive set of tables which predicts the percentages of both the male and female population that can move the weight of the object. The Liberty Mutual Risk Control Team recommends that tasks should be designed so that 75% or more of the female work force population can safely complete the task.
Key components that first must be collected before using the Liberty Mutual tables are: Total weight of object Hand distance (distance away from the body) Initial hand height (hand height at start of lift) Final hand height (hand height at end of lift) Frequency (how often is this task completed)
The complete Liberty Mutual tables and their guidelines can be found at their website. Liberty Mutual Insurance also has provided calculators that will manually calculate the percentage for both the male and female populations. If the percentage is less than 75% for the female population, a redesign of the lifting plan should be created so that 75% or more of the female population can conduct the materials handling. The link to the calculator can be found here.
Rapid Entire Body Assessment The Rapid Entire Body Assessment (REBA) is a tool developed by Dr. Sue Hignett and Dr. Lynn McAtamney which was published July 1998 in the Applied Ergonomics journal. This measurement device was designed to be a tool that health and safety professionals could use in the field to assess posture techniques in the workplace. Rather than heavily reliant on the weight of the object being lifted, Dr. Hignett and Dr. McAtamney developed this tool based on the posture of the employee lifting the weight. Using a series of mathematical calculations and a series of tables, each activity is assigned a REBA score. To calculate the REBA score, the tool separates the body parts into the two groups group A and group B. The body parts assigned to Group A are: Neck Trunk
The body parts assigned to group B are: Upper arms Lower arms Wrists
Using the score of each body part posture in group A, locate the score in table A to assign a group A posture score. This score is then added to the Load or force. This sum is the score A.
Using the score of each body part posture in group B, locate the score in table B to assign a group B posture score. This score is then added to the coupling score. This sum is the score B.
Using score A and score B, the correct score C is assigned using table C. The score C is then added to the activity score. This sum is the REBA score. The REBA score is a numerical value between 0 and 4. A REBA score of 0 has a negligible risk level, while a REBA score 4 has a very high-risk level. The REBA score can also provide how quickly action needs to be taken for each REBA score.
Rapid Upper Limb Assessment The Rapid Upper Limb Assessment (RULA) is a tool developed by Dr. Lynn McAtamney and Professor E. Nigel Corlett which was published in 1993 in the Applied Ergonomics journal. Very similarly to the REBA tool, this tool was designed so that health and safety professionals could assess lifting in the field. The tool is mainly focused on posture. Using a series of mathematical calculations and a series of tables, each activity is assigned a RULA score. To calculate the RULA score, the tool separates the body parts into the two groups group A and group B. The body parts assigned to group A are: Upper arm Lower arm Wrist position
The body parts assigned to group B are: Neck position Trunk position Legs
Using the score of each body part posture in group A, locate the score in table A to assign a group A posture score. This score is then added to the muscle use score and the force/load score which assigns the wrist and arm Score.
Using the score of each body part posture in group B, locate the score in table B to assign a group B posture score. This score is then added to the muscle use score and force/load score which equals the neck, trunk, leg score.
Using table C, locate the wrist/arm score in the Y-axis and the neck, trunk, leg score on the X-axis to determine the RULA score. The RULA score is a numerical value between 1 and 7. If the RULA score returns a 1 or 2, the posture is acceptable but if the RULA score is a 7, changes are needed.
Equipment to reduce risk of injury
To help mitigate the risk of injury from manual material handling there are devices which can be used to help mitigate some of the risk of manual material handling.
Exoskeletons Exoskeletons are devices which can be used to supplement the human body when completing tasks which require repetitive motions or using strength to complete a job. Exoskeletons can be powered or passive. Powered exoskeletons are powered using a battery which will supplement the strength needed for lifting materials. Passive exoskeletons are non-powered devices that are focused on a specific muscle group.
Overhead cranes Overhead cranes or workstation cranes can drastically decrease the exposure to workers for lifting and moving heavy objects. These devices can assist the worker by mechanically lifting, lowering, turning, or moving a heavy object to a different location.
Handles and grip aids When lifting heavy materials, the grip matters. By using handles, the grip could drastically change the posture of the lift. It can also reduce pressure points while lifting.
Forklifts Forklifts are powered vehicles (gas, diesel, electric) that are often used in facilities to move heavy items. The truck can pick up significantly heavier objects compared to the human and move it to a new location. Since the forks can be adjusted, the height of the lift can also be adjusted so that employees can lift in a more neutral position. The use of forklifts can eliminate or reduce some exposures of manual material handling.
Pallet jacks Depending on the weight being moved, manuel or powered pallet jacks can assist in moving heavy objects. If the weight exceeds an individual's capacity to easily push/pull, alternative means should be considered such as a forklift or a powered pallet jack.
Adjustable workstations The workstation height is critical to posture and preferred ergonomic principles. If the workstation is properly adjusted, it can prevent bending over and exposing the worker to awkward posture. Having an adjustable workstation can also allow the employee to adjust the height based on their height so that they can perform their work using good ergonomic principle.
Ways to reduce risk of injury