Fire Safety

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Fire Safety Priorities

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The fire safety code has 4 priorities for building.

1. Affor protection or escape for the occupants of a building. This may be accomplished by either of two means: evacuation from the building (egress), or moving objects to a protected area called Area of Refuge.

2. Insure sufficient structural integrity in the building so that fire fighteray enter and fight the fire with out excessive risk of collapse.

3. Is the least significant, but allow building to survive a fire so that it may be economically restored.

4. Prevent fires from stsrting, or once they have started, to extinguish immediately and automatically.

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Building code

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The architect must classify the building by its function, its construction type, and its location.

Occupancy: listed in IBC chapter 3, ranges include, but not limited to assembly to business, education, factory, hazardous, residential, and storage.

Construction type. There are 5 construction types. Type I and I are both built with noncomnistoble materials, type III includes noncomnistoble exterior s wallsand any material (accepted by code). Type IV is heavy timber construction and type V is any material approved by code.

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Compartmentation

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When a structure has mixed occupancies the construction of the walls separating them must have a fire rated separation of at least one hour but could be more depending on the occupancies.

When a design requires more floor area than is permitted by its occupancy, the space may be separated into two or more portions, each must comply with exciting and other requirements as if it was two different buildings. The walls and floors seeing the compartment must have a fire rating of 4 or 2 hours depending on the building type.

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Exits

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Exit passageways are required to be provided in every building for every possible spot in the building. The number is determined by the occupancy load and occupancy classification. An exit must be within 200ft (or 250ft if sprinklered). A 300 ft long building would need 3 exits. Passageways must be at least the occupant load served times .2 to get minimum width in inches. Cannot be less than 44" wide. All doors must swing outward and either be unlatched or have panic hardware. All exits must be fire-resistive construction. If four stories or higher walls or Type I or II-F.R. require a minimum of two-hour construction. One hour is acceptable for all other construction types. Large floors should be subdivided to stop fire spread. All wall penetrations in the separated wall must be fire-rated.

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Classes of fires

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There are different classes of fires that require different methods/materials to extinguish them.

Class A - ordinary materials that can be extinguished with water.

Class B - involve flammable gasses or liquids (oil, gasoline, or natural gas) where they float on top of water, so extinguishing with water is ineffective.

Class C - involve electrical equipment, and extinguishing agent must be electrically non-conductive, therefore water is unacceptable.

Class D - involves combustible metals and require special extinguishers.

Special extinguishing media - Halon does not use water and is not toxic in small exposures and extinguishes fires by removing/displacing oxygen. Good for computer applications or sensitive material such as artwork.

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Fire detection

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There are three types of fire detection available: ion detectors, photoelectric detection, or temperature sensing.

Ion detection: responds to the chemical products of combustion present in the air during a fire, even in the early stages. Batteries should be checked periodically. One problem is that the ion detectors also detect smoke from kitchen or cigarettes. Lower costs have now made this type the most popular.

Photoelectric detectors: detect smoke in the air that blocks a beam of light. May measure over a large volume of air but may miss the early signs of a fire.

Heat actuated detectors: detect heat in a room. Does not go off until heat reaches a specific limit. Rarely cause false alarm but usually actuated to late to save room fire begins in.

Other functions that may be set in motion by alarms. Actuating remote alarms in building or at fire station, other extinguishing elements, overriding elevator controls, closing fire doors, fire dampers, varying fan speeds throughout mechanical equipment systems.

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Dry standpipes

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The dry standpipe are large diameter water risers that are normally empty and not connected to water supply. Lower end is at street level where Siamese fitting is located. Used for fire pumper trucks to hook up and provided water to be accessed by fire fighters at the required levels. Typically located in fire stairs. Ball drip valve located at bottom of pipe to make sure it stays dry.

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Wet standpipe

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Wet standpipes are required for buildings four or more stories in height, most places of assembly, all hazardous and I, B, S, and M occupancies. Also equipped for Siamese fitting for fire trucks to provide additional pressure and flow rates. Must be located where every part of the building is within 30ft of the end of a 100ft hose attached to outlet. Must be designed to supply at least 35 gpm at 25 psi for 30 minutes and the water supply system must be adequate to provide 70 gpm at 25 psi for 30 mins. If building is more than 150ft tall a combination standpipe must be provided.

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Sprinkler systems

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The IBC requires automatic sprinklers in some occupancies and recommended in others. With some exceptions sprinklers are required in basements of all buildings (except for residential), any concealed spaces above stairways in schools, hospitals, and prisons, and places of assembly. All places of assembly over 12,000 in area and retail over 12,000 sqft per floor or 24,000 sqft gross. If fully sprinklered the code allows increases in height and allowable floor area and space between exit stairs.

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Wet and Dry sprinkler systems

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The simplest type of sprinkler system consists of a pattern of sprinkler heads, each with a fusible plug/link that melts in the event of a fire or high ambient temps and water pressure in pipe will cause a spray to flow through the head. Wet systems have the advantage of quick response and low initial cost but it's disadvantages include possibility of freezing and unnecessary wetting of building contents. To overcome the freezing problem, the dry pipe system was implemented. The pipes are filled with compressed air and pipe valve is located in warm area. The disadvantage is when activated nothing comes out which could cause a dangerous time delay in long pipe runs. Both systems only cause activated sprinkler heads to be discharged.

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Preaction systems

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Is a vairation of the dry system that requires that both the sprinkler head be activated and an independent fire sensing device be triggered. Avoids accidental discharge of sprinklers and resulting water damage. It is not a fail-safe as either wet or dry systems. Only cause activated sprinkler heads to discharge water.

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Deluge Sprinkler systems

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Based on the idea that if there is a fire somewhere in a space, wetting of the entire space is the safest action. This is generally reserved for areas of high fire hazard. In the deluge system all of the sprinkler heads are wide open at all times, but pipe is empty. Release it water is actuated by heat/fire detection in the area to be protecte, which activates the valve, flooding the system with water.

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Hazard levels

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In order to determine how great an area may be served by one sprinkler head, three major hazard levels have been established.

Light hazard: identifies areas where the quantity if combustible material is relatively low, such as churches, hospitals, museums, offices, and residential occupancies.

Ordinary hazard is subdivided into groups 1, 2, and 3. Group 1includes car garages and laundries, 2 includes large stack room libraries or publishing plants, and 3 includes paper processing plants.

Extra hazard is the greatest degree of hazard and applies to areas such as aircraft hangers and explosive handling areas.

Sprinkler heads must never be repainted which ruins sensing capabilities.