Systems Approach Vital to Design Of Early-Alert Detector Installation

Systems Approach Vital to Design Of Early-Alert Detector Installation

A discussion on fire detection systems and devices can take many forms, most of which are complex and very technical. The disciplines needed for accomplishing a successful and technically sound system are many and varied. A knowledge of building construction is required. A full understanding of heating, air conditioning and ventilation is vital. The nature of the fuel hazard and the conceptualized growth of conditions leading toward a collision course with self-sustaining and flaming combustion must be fully studied and appreciated. The consequent growth of a fire and the nature of its effluent now become matters of prime importance. Add to all this the applicable provision of the Life Safety Code, NFPA 101, and one truly has then an overall situation which can only be tackled by a systems approach. This is only a starter.

To begin with, there has been a great deal of research done on the prefire syndrome relating to:

  1. Early fire development, i.e., the slow incipient oxidation nucleous which, if both sufficiently aerated and insulated, will feed off its own emanated heat to permit growth followed by
  2. A commencement of the smoldering phase with the nucleous growing and aeration becoming deficient.
  3. The beginnings of evidence of the generation of carbon monoxide accompanying a relatively substantial smoke development.
  4. Combustion shifting from glowing to an eruption of open flame due to appreciable combustible gas generation.
  5. Flame radiation progressively bringing more combustibles into the fray with the fire growing according to the same principles as compound interest grows.
  6. Temperature rate-of-rise becomes now appreciable, followed by a noticeable increase in room temperature due to the combined effect of the heated combustion gases and flame radiation. We are now on the road to a real fire!
  7. Open stairways or, just as bad, closed stairways with doors hooked open, are an open invitation to rapid fire spread and are death traps.

The first three phases may take a considerable time (one to three hours), examples of which could be careless disposal of smoking materials, defective or overloaded electric wiring, transformers, etc., overheated climate control equipment, spilled household bleaches, rags containing unsaturated oils and many more.

On the other hand, these first three phases may practically not exist in that a lit match thrown into a wastebasket, a pilot flame for a a gas appliance igniting flammable vapors from an open paint can, a power mower being gassed up while running, immediately cause flaming with rapid temperature build-up and smoke generation if the fire is not free-burning.

The research mentioned above has resulted in the establishment of certain definite observations which will form the basis for our discussion, namely:

For the slow smoldering fires:

Temperatures within dwellings ramain nearly ambient until such time that flame erupts (Step 4).

Smoke-actuated devices operate prior to the development of serious concentrations of carbon monoxide or smoke.

Because of the impaired visibility within a building due to smoke, people (including fire fighters) could not rely on sight for evacuation, even before heat-actuated devices operate.

Disabling and near-lethal concentrations of carbon monoxide gas are recorded prior to the sounding of all types of heat-actuated alarms.

The above observations hold for a given space. Wall and door barriers will alter this picture. Detection calls for providing for each space.

For rapidly burning fires:

Shortly after ignition and before serious carbon monoxide or smoke concentrations develop, heat-actuated devices operate.

Ionization-type products-of-combustion detectors will also operate but optical smoke detectors will only respond when free burning stops and more fuel becomes involved, causing under-aeration.

For all types of fires:

Ceiling locations of detectors are paramount for all cases of rapid detection and for all types of detectors.

Wall locations of detectors are undesirable and must be avoided.

The increase of ceiling heights above 11 feet can cause problems together with cross ventilation that cannot be answered directly. Each installation must be the subject of an engineering survey.

By now, it must have become clear that there is no substitute for an early detection system and all that it entails for many locations, not only hospitals and nursing homes but also schools, residential occupancies, etc. This is a truism regardless of the type of fire for it is the only means of extending those precious minutes of borrowed time in handling considerable numbers of persons suffering from physical or mental illness, disease or infirmity, and for the care of infants, convalescents or aged persons.

Steps to be taken

Now to improve the proper system, three extremely important steps have to be taken, any one or more of which are absolutely meaningless and inconsequential if all of the remaining are not correctly done.

Step 1. The occupancy hazards must be identified as to the fuel type and loading. The compartmentation plays a very important role. We are not only concerned with spaces occupied by patients but also hidden spaces, closets, false ceilings, attic and basement areas including maintenance and work areas. Corridors and stairways become matters of vital concern.

Step 2. The type of detector (ionization products-of-combustion type, optical smoke, infrared or ultraviolet flame detector, rate-of-temperaturerise type, fixed-temperature type) selected will depend upon the fire development syndrome previously mentioned.

An engineering survey must be performed by knowledgeable, reputable representatives of manufacturers of Underwriters’ Laboratories listed apparatus.

It must be thoroughly appreciated that any alterations, additions, or modification of any type to an occupancy made subsequent to an existing installation requires a new look for adequacy of detection and whether or not changes are to be made regarding fire detection.

Step 3. Installation. Following the receipt of plans certified by reputable manufacturers and their authorized representatives, they must be reviewed and evaluated by responsible fire protection officials, insurance officials and officials of the state fire marshal’s office.

Testing and maintenance

When a given proposal is accepted, the final phase of testing and periodic maintenance now enters the picture. Just how to test the system now becomes the prime factor. The method of test-out must be a performance requirement inserted into the original proposal. If the hazard is of the slow-start, smoldering type of fire growth, a method has been devised by the General Services Administration and the military wherein 2 ounces of crumpled computer read-out paper is placed in a metal plate which is then located at what is judged to be the most remote from the detectors, not only with respect to distance but also with regard to obstructions and ventilation. Under these conditions it is required that an alarm sound between 30 to 60 seconds following ignition. If the alarm sounds earlier or later, corresponding adjustments are made to achieve the designated time limits, following which the system must hold for 90 days. At that time, if no premature false alarm occurs, the system is accepted.

Periodic reinspection, cleaning and re-test shall thence be performed every six months, using these same techniques.

Fast fire build-up hazards are most quickly picked up by infrared flame detectors and/or rate-of-temperature rise detectors (15 degrees/minute). An anticipatory thermostat type of detector is a form of rate-of-rise detector. Fusible link devices are impossibly slow in response to be of any value, unless as in the case of an automatic sprinkler, water is dispensed thereby on an actual open fire. Therefore, automatic sprinklers will also respond later than a well-designed fire detection system, and cannot be considered an alternate.

In closing, it must be emphasized that hospital and nursing home staffs must have personnel who are directly responsible for the proper service, maintenance and testing of fire detection devices. They have a terrible responsibility, but if done in a thoroughly honest and professional way will go a long way in providing the optimum protection and not just the minimum which every standard ever written has been written for. Standards are constantly being upgraded; use the latest ones and not the older ones of five or eight years back which were in effect the last time the legislature found the time to consider them. Human life is too precious to be jeopardized by avoidable inaction.

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