ATTIC VENTILATORS AFFECT FIREFIGHTER SAFETY

ATTIC VENTILATORS AFFECT FIREFIGHTER SAFETY

BY HARRY J. OSTER

During hot weather, temperatures in an attic space can rise well above 1007F if the attic is not properly vented. This heat buildup can be released and lowered in a variety of ways.

One effective way to reduce the heat buildup in an attic is to use an automatic powered attic ventilator (APAV).1 This type of ventilator operates automatically through an adjustable thermostat within the ventilator`s housing and can be found on the roof of private homes, low-rise multiple dwellings, and some industrial or commercial buildings. You can check for the presence of an APAV from the exterior of a building by looking in the area of the ridge or peak of a peaked roof for a circular object about two feet in diameter and about nine inches in height. If the roof is flat and has a parapet, the presence of an APAV most likely will not be detected until a firefighter ascends onto the roof and visually checks for its presence. The factory color of APAV covers (also called domes), typically made of plastic or metal, will vary. Popular colors include white, brown, and silver. Keep in mind also that for building-enhancement purposes, building owners sometimes paint the covers to match the color of the roof shingles. This enhancement could make it difficult to detect the presence of an APAV during the initial quick size-up of the building and roof.

This type of ventilator (less cover) can also be hidden out of sight behind the louvered gable vents located in the side portion of the building`s attic space, just below the underside of the roof. If on arrival at a reported incident scene you see smoke pushing out under pressure from a gable or roof vent, anticipate that an automatic powered attic ventilator may be behind that smoke. An APAV might be looked at as “a form of uncontrolled positive ventilation” that can create hazardous working conditions for firefighters on the roof because the fire could be pulled more quickly across the roof toward this type of ventilation.

FIREFIGHTER AT RISK

Let`s look at some of the risks this type of ventilator may present for firefighters. If a fire starts or extends into an attic space, the ventilator would turn on, sensing the heat buildup at about 1057F.2 The ventilator does not know the difference between heat buildup from a fire or the sun. Therefore, with a blade/motor speed of an APAV averaging between 1,000 and 1,500 revolutions per minute (rpm),3 an APAV could “pull” the heat, smoke, and flame toward an APAV in operation more quickly than if the ventilator was of the natural draft type.4 The rate at which an APAV moves air generally averages between 1,000 and 1,600 cubic feet per minute (cfm).5 For the reasons just mentioned, the automatic powered attic ventilator could affect a firefighter and the fireground operation in the following ways:

It could mean less, or even no, time for roof operations.

The potential for injuries increases due to undetected earlier structural failure of the wooden roof rafters (especially with lightweight wood trusses) and plywood roof sheathing.

POSSIBLE SOLUTIONS

When heat buildup from a fire or the sun causes an APAV to activate–and if the ventilator is equipped with a type of external ambient temperature sensing switch, such as a firestat located next to and wired into the unit–the APAV will shut down when the ambient temperature next to the ventilator reaches 1657F.6 This setting temperature (1657F) is a fairly common setting for firestats, which are readily available from an electrical supplier. A firestat has a red, four-inch circular metal plate with about a three-quarter-inch-diameter raised black button in the center. Without this firestat, an APAV would continue to run and pull the heated gases, smoke, and flame through the attic and through the APAV until the motor reaches its internal thermal protection temperature, which is understood to be about 2507F,7 which in theory should then shut down the ventilator. The ventilator could also be shut down when the heated gases or flame melts (at an approximate temperature of over 3007F)8 the plastic covering off each of the two conductors on the wire leading to the ventilator. Again, when this happens, the two bare wires theoretically should touch and cause a short circuit that should shut down the ventilator motor.

Installing a firestat to sense and react to the ambient temperature (the temperature of the space around the ventilator) within the attic space instead of relying on the internal thermal protection feature or a short circuit could be quicker, more practical, and safer for the firefighter as well as for the homeowner in that it may result in less property loss.

Another way to shut down this type of ventilator effectively would be to wire a heat detector located in the attic space into the ventilator or, at the very least, wire the ventilator into the hard-wired smoke detector system located within the building`s top-floor living space. However, the concept of wiring the ventilator into a hard-wired smoke detector within the building`s living space may not be the best solution. It would probably not shut down the ventilator if the fire started in the attic, but it would shut down the ventilator if the fire started within the building`s living space, especially if a fire occurred on the top floor.

A simple solution might be to manufacture these ventilators with a built-in firestat or high-limit external ambient sensing thermal protector, similar to the type used on recessed lighting fixtures, that senses heat buildup around the external surface of the fixture housing. However, a manual reset device might be better suited to a ventilator than the automatic reset device prevalent on recessed lighting fixtures.

CHANGES TAKE TIME

Currently, your local code may be vague about the requirement of having a specific type of ambient temperature shutoff provided on automatic powered attic ventilators. That section of the code may also be very broad instead of specific about APAVs. The code may state only that “attic fans” be provided with the means for automatic shutoff in case of fire. This could be misinterpreted in many ways, such as “if the motor has the internal thermal protection feature, the safety requirement is satisfied” or “this only applies to the larger whole house fans located in the hallway of the top floor of a building`s living area” or “this requirement applies only to a fan-type appliance that is rated over X cubic feet per minute.”

Again, the objective for having an ambient temperature sensing shutoff-type device on or within close vicinity of an APAV would be to obtain a fast and ac-curate reaction time to the heated gases, smoke, or flame. This would allow time to slow down the fire`s spread rate and give responding firefighters a chance to extinguish and controllably ventilate a smaller fire. This is especially important to a firefighter assigned to perform ventilation operations from the roof position.

Although the above enhanced solutions sound effective, they cannot be implemented immediately. Generally, it takes time to effect changes in codes. Many proposed code changes first need to be thoroughly researched to determine if a change to the code is warranted. Often the major roadblock to a change is the additional cost factor for the manufacturer and the consumer. Also, any new approved changes take time to flow into the field. If not specifically spelled out, they could lead to gray areas of interpretation that could result in debates between the authorities having jurisdiction, the contractor, and the owner of the building.

Lastly, if a change were approved, the following would need to be addressed: What about preexisting APAVs? Would they be grandfathered as they are? Would there be a special building inspection for buildings that have this type of ventilator, or would the existing APAVs be updated only if and when the authority having jurisdiction inspects the building for whatever reason?

OPERATIONAL CONSIDERATIONS

When sizing up a building on arrival, look to see if the smoke is pushing out under pressure from a location in the roof or gable portion of the attic. If so, think APAV.

For safety, DO NOT play “polo”: Do not rapidly remove an APAV cover with a tool as you would in the case of a natural draft-roof vent. With four to six blades comprising a total diameter of 14 inches and turning at an average speed of 1,200 rpm, a tool can become lodged in the fan and pull firefighters off balance and cause them to land on the unit, pull firefighters into the unit, or cause firefighters to be hit by fan or tool parts that have been sheared off.

If the cover is removed and the fan cannot be stopped, the fan will continue to pull and will emit more unrestricted air containing smoke, heated gases, and flame than if the cover were left on until power to the ventilator has been cut.

Relay to the incident commanders and other firefighters over the radio that an APAV is present and what the fire conditions are in and around the unit. This information will enable the IC to plan a more effective strategy for controlling the fire and to direct a member to locate the electrical panel and shut down the power to the APAV or building.

Depending on fire conditions in the attic space or on the top floor–and while waiting for the power to be cut–commence other key roof operations: remove the covers of natural roof vents and skylights, look for bubbling tar to determine the degree of fire extension, look over the edge for trapped occupants at windows, cut and inspect a primary vent hole over the fire, try to determine the type of roof construction (truss, for example), and so on.

Whenever possible, perform roof operations with the wind at your back to keep smoke and heated gases away from you.

LESSONS LEARNED AND REINFORCED

Preplanning through routine building inspections perhaps would be the most effective way for a firefighter to prepare for an incident that could involve an automatic powered attic ventilator.

Often, codes are not clear enough. They often lack the who, what, where, when, and how substance. For example, instead of using the words “attic fans,” the section should be explained completely: “This section of the code shall pertain to automatic powered attic ventilators starting from X inches in diameter and having a minimum cfm rating of X, and which are located in the attic space of a private home, low-rise multiple dwelling, and industrial or commercial occupancy.”

Congratulations if your local code already specifies that a firestat or similar type of device be installed on APAVs. However, if your code does not currently require this feature, perhaps you may want to consider initiating a public education campaign that stresses the importance of having a firestat or other ambient temperature sensing devices for an APAV from a firefighting standpoint.

I`ve had many casual conversations with firefighters, code enforcement officers, electricians, and homeowners about automatic powered attic ventilators. In most cases, they became defensive because they first thought “whole house fan” (again, the type of fan/ventilator typically located in the top-floor ceiling of a private home, which, I believe, is required to have an external thermal protection cutoff feature). When I told them exactly the type of fan to which I was referring, they replied, “Oh, that little thing in the attic.” Again, this reinforces the observation that interpretations, conversations, and statements directed at a specific object, such as an APAV must be made crystal clear. n

The author`s views do not necessarily reflect the views of other members of the fire service, career or volunteer. This text is for informational purposes only. Before applying this information in the field, departments/individuals should seek legal and safety advice and engage in technical research.

Endnotes

1. An abbreviated term to describe an automatic power attic ventilator I developed for this article.

2. Generally, the APAV`s preset activation setting. However, this setting typically can be field adjusted to between about 707F to 1307F.

3. This is based on technical data sheets of various manufacturers of this type of product.

4. A natural draft turbine-style roof vent of similar roof opening size would typically produce about 700 cfm at a wind speed of four miles per hour.

5. This is based on technical data sheets of various manufacturers of this type of product.

6. This is based on the most common availability at a local electrical supplier.

7. The temperature generally established by the manufacturer.

8. This is based on a simple “oven bake” test I performed.

This illustration shows how the elements of a fire (heat, smoke, and flame) could be pulled to an automatic powered attic ventilator (APAV). Here, the fire started on the top floor of a building and penetrated the attic space. If the APAV was already on, because of hot weather, these elements would instantaneously be pulled in the direction of the APAV. If the ventilator was not in operation, once the attic space filled up with the elements, the APAV would sense them and come on at its activation temperature, generally about 1057F. Once on, it could pull the heated elements toward the APAV. In the process, any wood rafters, trusses, or plywood between the area where the fire penetrated the attic and the APAV could be weakened by these elements, creating a hidden “danger zone” for firefighters on the roof.

A gable vent. Is a ventilator behind those slats? Also, if a fire self-vented through the window with the air-conditioning unit and if the ventilator were located in the gable vent at the other end of the house, once activated, how fast could the fire be drawn up, into, and across the attic space through this gable vent? (Photos by author.)

(Top left) The ventilator and the firestat. Note how the firestat is placed between the ventilator and the ridge board (the topmost section of the roof). This will enable the firestat (set at 1657F) to sense the ambient temperature of the heated gases as they are pulled toward the ventilator. This can shut the unit down when the firestat`s temperature is reached. (Photos by author.) (Top right) The attic space of a new low-rise multiple dwelling. The rise of the roof is approximately 20 feet. If a fire were to occur, the heated gases, smoke, or flame could be pulled to the ventilator once it has been activated and may cause the fire to intensify. Where`s the firestat or smoke detector? (Bottom left) A ventilator in a condominium low-rise multiple dwelling. Note the natural roof vents as well. It is possible that each unit has its own ventilator. Therefore, it`s also possible that either a fire wall, a fire-rated separation, or draftstopping terminates on the underside of the roof`s plywood sheathing for each unit. What about the possibility of voids? (Bottom right) Generally, the ventilator dome is made of plastic or metal and protrudes from the roof about eight inches. It is about 24 inches in diameter. This ventilator is located near the center of the roof. Occasionally, it might be off center near the front or rear. But in almost all cases, it is near the ridge area of the roof, unless it`s concealed behind a louvered gable vent of the attic.

A recessed light fixture. Note the external thermal protector of the automatic reset type (near the lower left-hand corner of the photo). It can be identified by its black cylindrical appearance.

(Left) While operating with the wind at your back, DO pull the cover off natural roof vents. (Right) DO NOT pull the cover off an automatic powered attic ventilator. Severe injury or enhanced flame travel may result. Relay the presence of an automatic powered attic ventilator to the incident commander, and request that the power be shut off. Always operate with the wind at your back.