By Michael Nicasio, Principal Engineer, Fire Containment and Fenestration

Hardened building design can focus on multiple potential risks with the fundamental purpose of protecting occupants and property. One potential risk in the U.S. is severe storms, such as tornados and hurricanes.

According to the National Oceanographic and Atmospheric Administration,1  the U.S. recorded an average of 1,222 tornado reports annually from 1990 through 2021. The total number of tornadoes reported in 2023, confirmed and preliminary, trended slightly higher to an average of 1,294. The coastal regions along the Gulf of Mexico and the Atlantic Ocean have seen similar changes in recent years, as reported by Time magazine.2 At least one Category 4 or Category 5 hurricane has made landfall in the U.S. each of the last five years, where Category 5 is the most severe hurricane. Of the nine Category 4 or Category 5 storms recorded in the past 50 years, six have occurred in the past seven years. It was also reported that eight hurricanes impacted the continental U.S. from 2020 to 2021, compared to 19 hurricanes making landfall between 2000 and 2010. The growing concern about upward trends of tornado- and hurricane-type storms reinforces new regulations to further harden residential and commercial buildings against the effects of severe weather.

Where building structures or portions thereof require protection against extreme wind events such as tornadoes and hurricanes, the International Building Code (IBC), International Residential Code (IRC) and International Existing Building Code (IEBC) refer to ICC 500, Standard for the Design and Construction of Storm Shelters. Storm shelters are designed as hurricane shelters, tornado shelters, or combined hurricane and tornado shelters. ICC 500 covers storm shelter design, construction, testing, installation and maintenance, and establishes the minimum requirements to protect occupants during a storm event. The types of construction elements covered by ICC 500 can apply to the entire storm shelter or to components within the storm shelter used to protect the storm shelter envelope, referred to as impact protective systems. Impact protective systems can include building features such as doors, windows and louvers.

Since its initial publication in 2008, ICC 500 has seen many developments with the testing protocols and further consideration for the general health and safety of occupants within a storm shelter during an emergency. One specific aspect of evolved storm shelter design concerns the latching hardware. Latching hardware is critical in impact protective systems such as swing doors. In addition to retaining a door in place, the latching hardware allows entry and egress to and from the storm shelter during normal building operations or during a severe weather event. ICC 500 outlines several requirements for latching hardware to be (1) permanently mounted and operated without tools or special knowledge, (2) automatically latching unless signage is provided with instructions for latching, and (3) capable of multiple latching systems requiring more than one action as long as permanently installed instructions are provided.

During the development of the 2020 edition of ICC 500, the consensus committee on storm shelters established more concise language concerning the susceptibility of latching hardware becoming unlatched from the unprotected side by debris impact or other unintentional causes. Latching mechanisms on impact protective systems remaining in place is critical, as opening doors during a storm could compromise the integrity of the storm shelter, creating an unsafe environment for occupants. The requirement established that latching hardware is to be locked or inactive once the storm shelter hardware is engaged. The engagement of a storm shelter may include an automatic means incorporated within the impact protective system or a series of operations with posted signage and instructions for the full engagement of the latching mechanism. In either case, it is a best practice to keep the number of operations for latching and unlatching to a minimum to allow for quick and easy access and exit once the storm passes.

The locked or inactive latching mechanism can be achieved by fixing, locking or freewheeling the operable hardware on the unprotected side. Hardware manufacturers may offer several functions for the latching mechanism, so it is important to select the appropriate function to meet the requirements for the storm shelter and other normal daily operations.

UL certification of latching hardware is covered in UL Product iQ®  under the category ZHLL. Product iQ, available at www.UL.com/PiQ, is complimentary with a one-time registration.

Only latching hardware that meets the operability requirement is included within the listing. In addition, the UL Guide Card for Products for Use in Windstorm-Rated Assemblies includes the following text to provide further guidance regarding the topic of operable hardware within a storm shelter: “Impact protective systems intended for use with storm shelters as outlined in ICC 500 incorporate operational hardware requirements. Where operating hardware of an impact protective system is located on the unprotected side of the storm shelter envelope after the latching mechanism is engaged, such operating hardware on the unprotected side shall be locked, disabled or inactive, and shall not be susceptible to unintentional unlatching by debris impact. The use of these systems shall be determined by the authority having jurisdiction  and considered in conjunction with life safety and egress code requirements, where applicable.”

For questions or additional information, please contact UL Solutions at ULregulatoryservices@UL.com.

References

1. National Oceanographic and Atmospheric Administration’s National Centers for Environmental Information. www.ncei.noaa.gov.
2. Time magazine. (2022). Here’s Where All the Strongest Hurricanes Have Hit the U.S. in the Past 50 Years.  time.com/6218275/strongest-hurricanes-us-map/time.com/6218275/strongest-hurricanes-us-map/.

» Publication Date: 21/10/2024

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