written by
Ryan Penn

Understanding ASME A17.1 Safety Code: The 3/4" & 4" Rule Explained

Elevators Permits Safety Codes & Standards Technical 2 min read , May 18, 2023

Let’s explore the ASME A17.1 Safety Code for Elevators and Escalators. Specifically, we're going to focus on the 3/4" & 4" rule, which governs door clearances in hoistways. With the complexities of the elevator code, it can sometimes be challenging to understand how to apply these rules in practice. But fear not! We're here to break it down into easy-to-digest terms.

The Basics of the 3/4" & 4" Rule

The rule of 3/4" & 4" refers to the maximum hoistway door clearances mandated by the Safety Code. But what does this mean exactly?

  1. 3/4-inch clearance: For swing doors, the gap between the hoistway side of the landing door and the edge of the landing sill should not be more than 3/4" (or 19mm). For sliding doors, this clearance can be up to 2.25" (or 57mm).
  2. 4-inch clearance: The space between the hoistway side of the landing door (or gate) and the car door (or gate) should not exceed 4" (or 102mm).

These maximum clearances are essential for maintaining safety. They help prevent individuals or objects from becoming trapped between the elevator car and the landing door.

ASME A17.1 3/4" & 4" Rule

Eclipse Residential Elevator Design

For those working on the Eclipse Residential Elevator, it's critical to remember that the design includes a maximum running clearance of 1.25" (or 32mm). This specification is tighter than the standard 4" rule, emphasizing the manufacturer's commitment to safety.

Common Violations and Recommendations

The 3/4 & 4 rule might seem straightforward, but in practice, many structures tend to violate these standards. In particular, concrete block/masonry shafts and some commercial metal door frames often fall short of the clearance requirements. To mitigate this, we recommend the installation of solid doors. Hollow doors often fail to meet the pull-out force required by the code for door locks.

Additional Guidance

A few more tips to ensure you're meeting the 3/4 & 4 rule:

  • If the landing door has a pattern on the hoistway side, measure the 3/4” setback from the deepest part of the door to the landing sill. This helps ensure that even the furthest points on the door fall within the required clearance.
  • For accordion (panel fold) gates, you should install flush doors instead of having a 3/4" setback. This helps prevent the gates from intruding into the hoistway.
  • The 3/4" setback is achievable only when the car doors are bi-fold or slim doors. These door types can provide the necessary clearance without compromising safety or functionality.

In conclusion, the 3/4 & 4 rule is a crucial aspect of the ASME A17.1 Safety Code. As elevator mechanics and inspectors, understanding and applying this rule is fundamental to our work. It may seem like a small detail, but maintaining these clearances can make a significant difference in elevator safety.

As always, safety first!

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