Advances in coiling steel fire doors

The role of a rated coiling fire door is to close at a controlled rate of descent on a fire alarm activation (loss of power, alarm signal or melting of fusible link) and prevent the spread of fire from one side of the fire-rated wall to the other. The effectiveness of this type of door was demonstrated in 1996 when a fire broke out at a major warehouse. As shown in this photo, the 25 fire doors that were installed along the fire-rated wall between the warehouse and offices saved the company from incurring additional losses in property and potentially saving the lives of the working personnel.

Until recent years, most coiling fire doors were used solely for their fire protection abilities and remained in the full open position until a fire caused the fuse link to release the door to close. Since most specifications were for this design, there was little requirement for various modes of operation and optional features. Although the basic operation of the fire door has not changed since the early 1900s, recent advancements in coiling fire door product offerings have improved the testing, governing and activation of the fire doors.

Fire door drop testing

Per National Fire Protection Association (NFPA) Standard 80, Standard for Fire Doors and Fire Windows (1995 edition), Section 15-2.4.3, "All...rolling fire doors shall be inspected and tested annually to check for proper operation and full closure." If it were not for the considerable time and expense associated with testing most fire doors, this annual requirement could be upgraded to a more frequent basis to ensure the ongoing safety and operation of the fire door, specifically when dropped. Per NFPA 80, the door's drop speed should be maintained between 6 and 24 inches per second. Otherwise, if the door drops too fast, it could result in injury or damage; likewise, if the door drops too slowly, the fire could spread from one side to the other before the opening is secured. The only way to ensure the door releases properly as well as drops at a proper rate of descent is to drop-test the door on a more frequent basis.

In many designs today, there are drop-out mechanisms on both the charge and drive side of the door that release spring tension and disconnect the motor operator during a drop test. Since these drop-out mechanisms sometimes fall below the bracket plates, additional clearance is also needed so there is not interference. (If the door were directly above the ceiling, it would require a slot to be cut into the ceiling.) Spring tension is released to make the door unbalanced so it can start to drop. The motor is disconnected so the gear reducer will not hold it open. Consequently, after the drop test, the door technician first must open the under-balanced door since it is unsafe to apply charge with the door in the down position. Then the technician is hoisted to the charge side of the bracket plate and re-applies tension to the spring assembly. Finally, the technician is hoisted to the drive side of the door so the motor can be reconnected. Since the drop test requires reapplying tension to the charge wheel, only a qualified door technician can drop test the door with the traditional design.

Fortunately, a few manufacturers have developed products that make drop-testing the door a very simple operation and do not require a licensed door technician to perform the test. Instead of taking a few hours, adding additional costs in labor and creating down time in the door traffic area, the test can now be accomplished in just a few minutes by the end user. Consequently, the fire door can be drop-tested on a more frequent basis with no additional cost. This should ensure potential problems are identified and corrected much sooner than they are when relying on a test that happens only once a year.

In addition to the benefit of easier drop testing, most of these new designs fit within the dimension of the bracket plate since there are no dropout mechanisms that need re-setting. Besides the reduced headroom for these new products, no slots need to be cut into the ceiling to accommodate the drop-out mechanism.

Viscous speed governors

As noted above, once the door is activated to drop, the rate of descent must be controlled. This is accomplished through the use of a governor. Until recently, one of the most common designs was the oscillating governor. This is basically two cast iron parts (a ring and a gear) that ratchet into each other to slow the door down. This design is outdated, noisy and unreliable for most applications. Due to the high impact against the two cast iron parts, there is a greater chance for failure.

The latest type of governor is the viscous governor that uses viscous fluid shear to control shaft rotation. This design is much quieter and more reliable since there are no parts impacting against each other. The damping