Safety Analysis of Working at Height
Kang Chen, ASHRAE
Working at Height has been considered as a task with high risk profile for many years worldwide. A multitude of topics are discussed in this article such as Unprotected Openings or Edges, Walking & Working Surfaces, Portable & Fixed Ladders, fall protection and emergency response & medical treatment. Actively involved a wide variety of industrials, including pharmaceutical, fine chemical, pulp & paper, electronics and machinery, the author understands the special importance of risk control of Working at Height and would like share some technology based experience and know-how to raise workers’ awareness and enhance their knowledge in the file of Working at Height, a permit required activity.
Unprotected Openings or Edges
First and foremost for openings and edges protection is area cordon-off with clear and visible alert labelling. For some scenarios, just as working at a temporary construction site or doing outdoor activity without adequate illumination, serious injury, even loss-time injury can be happened when a person step into a very shallow pit (maybe 20 centimeters) without awareness of its risk. This was a real incident reported in the company of my previous employer and the unfortunate worker experienced a surgery and three-month rehabitation. Lacking of cordon-off lines and basic safety alert is the direct cause of this incident, which aroused all works’ attention and not too late for management reinforces working safety. Another equally important aspect is covering or sealing materials of openings. The covering material should sustain double weight from both works and equipment at least in order to make sure its durability and cannot be manually removed. Last but not least, safety net or safety cushion is good practice for alleviating injury seriousness which should be considered as well. Take safety net as an example, the mesh size should be less than 36 sq inches and either side length must shorter than 6 inches. The smaller distance between net and falling down surface, the better fall protection function is provided to the worker, and the maximum clearance cannot exceed 30 feet. Meanwhile, any obstacles under a safety net can be a potential risk and should be eliminated immediately before working at height activities to prevent obstacles derived hurt.
Walking & Working Surfaces
In many circumstances, most of us just focus on personal protective equipment (PPE) and then risks from Walking & Working Surfaces are normally neglected. Through incident statistics and data analysis report from UK HSE/HSL (Health and Safety Executive/Health and Safety Laboratory), cases happened during working on roofs and skylights account for one-fourth of total incidents in the past decades. Thus, the author would like to draw your attention on some topics of working at height, these topics include but not limited to fragile surfaces, working on roofs and skylights and working with Mobile Elevated Work Platform (MEWP).
There should be three hierarchies or more for risk control of roof work, which is almost the same as any other risk control strategy and methodology. Firstly, working at height related activities are highly recommended to be avoided by involving suitable tools and fixtures, or at least the frequency of those kinds of activities should be reduced as few as reasonably practical. Safe conditions can be attained in consideration of intrinsic safety application and using movable articulator to assist roof cleaning at ground level is just a case in point. Secondly, Mobile Elevated Work Platform (MEWP) should be utilized to reduce falling risk once working at roof is proven to be inevitable. Nevertheless, users must be properly trained and understand basic mechanical/electrical principles and safety requirements. Worker(s) on the platform should have primary control of the MEWP, whereas supervision staffs can only get operation priority upon emergencies or malfunctions of the MEWP. Two-way communication devices like interphones are always recommended to prevent crushing incident and even fatality by misoperation of MEWP. Furthermore, working environment, i.e. explosive atmosphere, inclined or sticky road surface, is an important factor indisputably need to be considered when using MEWP. On the other hand, MEWP is not almighty and cannot access to some very narrow areas or is blocked by some fixed obstacles in workshop. Consequently, setting up safe guardrail and safety net becomes the urgent need as alternative risk control solutions. These countermeasures are recommended to be taken if the potential falling height exceeds 10 meters.
In addition, roof hatch is widely installed in western countries and therefore attention should be paid on it. Usually, ladders are extended outside working surface for 3 feet at least and roof hatch is the exception oppositely. Below are some important reminders if roof hatch is installed at your location: a. Any sharp edge of roof hatch must be eliminated in order to prevent hand cut; b. Quick move should be avoided when getting in and out of the hatch. This is mainly due to the consideration of light and dark adaptation. The eye operates over a large range of light levels. The sensitivity of our eye can be measured by determining the absolute intensity threshold, that is, the minimum luminance of a test spot required to produce a visual sensation. Consequently, dark adaptation refers to how the eye recovers its sensitivity in the dark following exposure to bright lights. Aubert (1865) was the first to estimate the threshold stimulus of the eye in the dark by measuring the electrical current require. Light adaptation cost about one minutes and dark adaptation takes longer periods and various depending on person’s physical status. c. Two-way communication devices like interphones are mandatory for working alone on roof areas, especially via roof hatch for access. Also, roof hatch should be safeguarded with rails or hatch must be locked after work get to the roof area to prevent falling down through the roof hatch. Meanwhile, the bottom side of roof hatch should be labeled with self-luminescent material to prevent dead lock.
Portable & Fixed Ladders
Fixed Ladders are widely used as an access to elevated working surface. Unfortunately, these ladders are always found to be misused. Some typical unsafe behaviors or conditions include lack of lock out/tag out (LOTO) procedures and safety placards, working without PPEs and no landing platform at 30 feet height. Transitional working platform should also be installed connect two cage ladders. Ladder’s topside must extend outside working surface for at least 3 feet and handrail system should be fixed with 1100mm toprail, 550mm midrail and 150mm toeboard.
Portable ladder is another useful device for working at height not only at industrial facilities but also in commercial buildings. Maximum load and permitted working height are two significant parameters which will be demonstrated on the ladder’s label. American National Standards Institute categorizes portable ladder into civil-III, commercial-II, heavy industry-I and special heavy industry-IA, which have maximum load respectively from 200 to 300 pounds. Workers are forbidden to stand on the top three steps of an extension ladder and the top two steps of a stepladder. As universally acknowledged, metal ladders can never be used in corrosive environment (chlorosilane, strong acid and alkaline) or with electric shock hazard. Three-point contact with ladder is a very helpful principle for use ladder safely, either one hand with two feet or two hands with one foot.
Fall protection and first-aid
When calculating the theoretical falling height, the length of energy absorber and D-ring plus 3 feet as a redundant safety factor should be integrated. Swing fall, which can lead to serious injury and even cut off safety belt, must be prevented by proper anchor point design and selection. Good anchor point should always be located at the plane higher than one’s head. Even this is infeasible, the angle of swing fall is required to be limited as 30 degree below in order to reduce punching hazards.
As for Qualified Anchor Points, minimum load capacity is 22.2 KN according to ANSI standard and 10.0 KN in EN standards. Ideal Anchor Points include steel pipe with 3 inches diameter, I Beam and well-designed life line system. However, handrail, cable tray and scaffold can never be used as Qualified Anchor Points.
First-aid, the preliminary and crucial step in emergency response, should be emphasized and practiced periodically. Firstly, it’s important to understand the risk of suspension trauma, which is a common occurrence when talking about Working at Height related injuries. A force amplitude of about 500 kg will act on work’s body during energy absorber activation. What’s more dangerous, twenty seconds’ suspension can make most of your body blood converged at legs and then cut down venous return significantly, which leads to drastic blood pressure drop and ischemic brain disease, even brain death if this kind of suspension lasts for more than 5 minutes. Suspension Trauma Strap, used as a self-aid kit, can provide a standing platform to alleviate muscle pressure and accelerate blood circulation successfully. Works are recommended to seize or lean on any objective as possible as they can if there is no Suspension Trauma Strap available. Anyway, besides first-aid actions, considering how to rescue the workers safely and immediately should be prioritized as well during emergency response. Once the wounded is transferred to the ground, his head should be raised slightly to keep airway open and safety belt can be taken off thereafter. Last but not least, EAP (Employee Assistance Program) specialist should be resorted to as appropriate.
To sum up, Working at Height has become one of the high risk activities in various industries nowadays. Some technical requirements and best practices with regard to risk control are formulated in this paper, which can be used as preliminary training or learning materials. It’s absolutely impossible to cover all aspects of Working at Height and many other important topics are not explained here. Working on tank car/container truck, employee drug-free test, preventing slips and trips, Ice Alert Indicators application are just some examples may arouse reader’s attention for further analysis.
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