The Ins and Outs of Modern Doors: Everything you ever wanted to know about metal doors and more.

cpm: Why do the various hollow metal manufacturers have different fire labeling capabilities?

Smith: Each fire test is run for a specific company or for a specific group of companies. For instance, members of the Steel Door Institute (SDI) and NAAMM (National Association of Architectural Metal Manufacturers, Hollow Metal Division) run joint fire tests as a cost savings to their members. The labeling agencies such as Underwriters Laboratory (UL) and Intertek will fire-test anything that you bring to them, but that does not mean that it will meet building codes or National Fire Protection Association (NFPA) 80 - "Standards for Fire Doors and Fire Windows." There is sometimes a conflict between providing life safety (the ability to exit a burning building safely or find refuge in a stairwell), and security (making sure drug dealers don’t come in the side doors of a building during school hours). These issues need to be resolved during the design or remodeling process.

CPM: Why can’t an eight-foot door be fire labeled with only three hinges?

Smith: The answer to this question can be found by quoting the heading from NFPA 80 of Table 2-8(a):Builders Hardware. "Doors up to 60 inches in height shall be provided with two hinges and an additional hinge for each additional 30 inches of door height or fraction thereof. The distance between hinges shall be permitted to exceed 30 inches." Therefore, a 90-inch door can have three hinges. However, as soon as an extra inch in height is added to 91 inches, four hinges must be provided. (The exception to this is the use of one continuous hinge to hang the door.)Hardware, its installation and placement are important considerations in maintaining the integrity of the door and frame unit to restrict the spread of fire from one part of a building to another.

CPM: What is a temperature rise door?

Smith: A temperature rise door is used to retard the transmission of heat from one area to another. It is a measurement of the rise in temperature above ambient temperature of the nonexposed side of the door during the first 30 minutes of a standard fire test. The lower the degrees, the better the rating. The accepted norm is a 250-degree rise over 30 minutes. However, 450-degree and 650-degree temperature rise doors are available.

It is not required to have a temperature rise rating for a standard labeled fire door. However, doors can be manufactured to meet this criterion.

CPM: Where are temperature rise doors used?

Smith: They are generally used in stairwells of high-rise buildings to limit the temperature rise through the door into the stairwell for a period of time. This makes it possible for people to exit the burning building safely by passing the floor of the fire. For example, many dormitories on college campuses might be required to have temperature rise doors in their stairwells.

CPM: What is STC?

Smith: STC stands for Sound Transmission Class. It is a measure of how much sound will be prevented from being transferred from one area to another. The higher the rating, the less sound can be heard on the other side. This is a logarithmic progression, as opposed to a linear variable. Therefore, on the average, a jump of three STC numbers (for example from 37 to 40), doubles the performance. Various STC Value ranges and their descriptions are listed above.

CPM: How does an acoustic door and frame assembly differ from standard hollow metal?

Smith: Generally, the performance of sound control doors is based in large part on the mass of the door. Sound doors are heavier than conventional hollow metal doors. Since their weight can vary from 10 to 20 pounds per square foot (210 to 420 pounds for a three-foot by seven-foot door), it is important to specify proper heavy-duty hardware capable of handling the door weight over the life of the installation. Also, the door frame is made of thicker materials than those used to hang a conventional hollow metal door, which weighs seven to eight pounds per square foot.

In colleges, these doors can be found in music practice rooms, radio or TV broadcast stations, mechanical equipment rooms and conference rooms.

CPM: What is the typical application for galvanized products versus cold rolled steel?

Smith: Galvanized doors and frames are used in exterior applications to prevent rust, especially in areas where there is spray from salt water. They are also found in waste water treatment plants and other areas with chemicals in use, such as chemistry buildings.

CPM: What do the different types of stainless steel mean?

Smith: There are four major groups of stainless steel. The Austenitic Group contains the 300 Series Alloys, which are most commonly used in the door and hardware industry. The stainless steels in this group are known as the chrome-nickel series. The two most common alloys used by the door and frame manufacturers are type 304 and type 316. Type 304 is your basic alloy. Type 316 contains a higher nickel content and is corrosion resistant.

CPM: What is the difference in the various finishes associated with stainless steel?

Smith: There are numerous surface finishes for stainless steel. The most common for doors and frames are Nos. 3 and 4 (very similar), or No. 8. No. 3 and No. 4 finishes are general-purpose polished finishes obtained with abrasives, and may or may not be additionally polished during fabrication. The common industry term for this finish is "satin." No. 8 is commonly termed a "mirror" or "polished" finish. It is the most reflective finish that is commonly produced. The surface is essentially free of grit lines.

CPM: What is the typical application for stainless steel doors and frames?

Smith: Stainless steel doors and frames are quite often found in food service areas because they can take repeated washing with hoses and not corrode. Other areas are swimming pools and animal care areas.

About the Author

Rachel Smith is senior interface designer at the California State University Center for Distributed Learning.

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