Ah, I think everyone has experienced tripping while rushing up the stairs and hitting their chin at least once. I, too, have injured my knee while hurriedly climbing the stairs due to the protruding part. Recently, I came across a comment on YouTube asking why those protruding parts exist, as they can cause injuries when people trip. So, I investigated. To put it simply, it turns out that those protrusions are intentionally designed for pedestrian safety when going up and down stairs.

We often encounter stairs, but surprisingly, we know very little about their structure. Stairs consist of a combination of treads, where we place our feet, and the risers, which are the vertical parts. The slightly protruding part where the tread meets the riser is called the stair nose. This stair nose is the main culprit that causes shin injuries when we rush up. Interestingly, it is even permissible to install this stair nose according to the law.

Most people are unaware that regulations exist. According to the detailed standards in the Enforcement Rules of the Act on the Promotion of Convenience for the Disabled, the Elderly, and Pregnant Women, the width of the step plates that can be used by disabled individuals, the elderly, and pregnant women must be at least 28 cm, and the height of the tread must be no more than 18 cm. This sets a minimum standard to ensure sufficient width, while the law specifies that the height of the tread should not be too high. Additionally, the slope of the tread surface is set to be at least 60 degrees to prevent toes or crutches from getting caught at the edge, and the step nose must not protrude more than 3 cm. Ideally, I would prefer to eliminate stairs altogether, but I wonder why it was stipulated that it should not protrude more than 3 cm. I asked No Chang-kyun from the Korea Institute of Civil Engineering and Building Technology, and he explained that the step nose has a psychological safety function. If someone falls, their body tends to move backward off the stairs.

When the center of gravity is shifted like this, people instinctively lean their upper bodies slightly forward. Psychologically, it can also create a sense of unease. To understand what this means, we first need to look at how our body’s balance changes when we go up and down stairs. Climbing stairs is a surprisingly challenging exercise, not only because it opposes gravity but also because it involves shifting the center of gravity from left to right. When standing still, body weight is evenly distributed across both legs, but when climbing stairs, the weight shifts to the back foot. Typically, when we step on stairs, we do not use our entire foot; instead, we primarily push off with the balls of our feet. To prevent the center of gravity from leaning backward while climbing stairs, the upper body also leans forward to some extent. For healthy individuals, this is not a problem.

However, in the case of the elderly or disabled individuals, more attention needs to be paid. A comparison of movements when ascending and descending stairs between the general population and the elderly, using video equipment like infrared cameras, showed that many elderly individuals tend to step on their heels more than the general population. The heel area corresponds to the tip of the foot where it touches the stair. When a person’s center of gravity is aligned in a straight line, it tends to concentrate towards the heel. If the back part of the heel is blunt, while the body wants to maintain its center of gravity at the front, it can lean backward. Some individuals ascend stairs using only the balls of their feet, but when they feel stable, they tend to push their feet all the way inside the stairs, which gives them the most stability. Still, in a rush to ascend, they may encounter difficulties on the stairs.

I asked again if there was a risk of falling due to the core, and the response was that stairs are meant for walking, not running. Jumping up or similar actions are considered special cases when designing stairs or walking facilities. These facilities are intended to support safe movement, so they are designed to allow for the safest walking experience. Additionally, when installing stairs, it is recommended to have rest areas every 1.8 meters from the floor level. This recommendation is also made with the safety of the elderly and other vulnerable populations in mind. In reality, it is somewhat constrained to accommodate all situations, so the safest design for the majority of users is typically sought, and facility standards are established accordingly. If you also want to request coverage, please let me know.

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