Why smoke detectors

Why Smoke Detectors? 

There is no mystery that building codes allow for the elimination of smoke detectors in various construction applications, but at the same time there is hard language in the code that mandates the use of the smoke detectors.

Smoke is a collection of airborne tiny solid, liquid, and gas particles produced by incomplete combustion (burning) or undergoes pyrolysis of materials, commonly containing carbon (soot), tar, ash, and various toxic gases. It is a byproduct of burning wood, coal, or other organic matter, with very small particles. It is treated as a major life-safety hazard, requiring engineered management systems to maintain tenable conditions.

Key Components and Characteristics of Smoke:

·        Composition: Smoke is a combination of solid particles (soot, ash), liquid droplets (tar, oils), and gas pollutants (carbon monoxide, nitrogen oxides).

·        Formation: It occurs when there is insufficient oxygen available for fuel to burn completely

·        Appearance: The visible grey, dark, or black color of smoke is primarily due to suspended carbon particles produced during combustion.

·        Behavior: Smoke forms a "smoke layer" during a fire, which NFPA 92 guidelines say should typically be managed to a minimum design depth (often 10% to 20% of floor-to-ceiling height) to keep exit paths clear.

Smoke occurs when there is incomplete combustion (not enough oxygen to burn the fuel completely). In complete combustion, everything is burned, producing just water and carbon dioxide. When incomplete combustion occurs, not everything is burned. Smoke is a collection of these tiny unburned particles. Each particle is too small to see with your eyes, but when they come together, you see them as smoke.

Smoke particles are extremely small, typically ranging from 0.01 to 1 micron (µm) in diameter. They often fall under the category of fine particles (PM2.5) or ultrafine particles (<0.1µm), and are much smaller than a human hair (~50-100µm) or bacteria (0.3-60µm). Open fire smoke particles are generally slightly larger, with peaks between 0.2 and 0.4 µm, but still mostly smaller than 1 µm. Optical smoke detectors generally detect particles in the 0.01 to 10 µm range.

Key Particle Size Details:

·        Tobacco Smoke: 0.01 – 1 micron.

·        Combustion/Soot: 0.01 – 0.3 microns.

·        Wood Smoke: 0.006 – 10 microns.

·        Synthetic Material Smoke: 1 – 50 microns.

·        Artificial/Fog Smoke: 0.2 – 0.3 microns

·        Cooking Smoke:

Natural Materials: Typically 0.01 to 0.1 microns.

Synthetic Materials: Can be much larger, ranging from 1 to 50 microns.

Cooking Oil (Smoldering): Generally 0.03 to 0.9 microns.

·        Surgical Smoke: Generated during medical procedures, these particles often fall between 0.01 and 1 micron.

·        Non-fire aerosol dust particles (interfering with detectors) are typically in the micron range, specifically 1–10 µm

A "True HEPA" filter is the gold standard, capturing 99.97% of particles as small as 0.3 microns. 

Types of particles that your HEPA filter should catch include:

·        Pollen: 10-100 microns 

·        Pet dander: 0.5-100 microns 

·        Dust: 0.5-100 microns 

·        Fungal spores: 2-100 microns 

·        Tree and grass pollen: 20-30 microns 

·        Ragweed pollen: 10-20 microns 

·        Mold spores: 2-20 microns 

·        Bacteria: 0.5-5 microns 

HEPA filters are effective at removing a wide range of particles from the air, there are some that they can’t catch. These include gases, odors, and chemicals.

Depending on the size, types of particles a HEPA filter may miss include:

·        Lead particles: 0.1-10 microns 

·        Combustion particles: 0.1-1 microns 

·        Smoke: 0.01-1 microns 

·        Viruses: 0.02-0.3 microns 

NFPA defined combustible dust as any finely divided combustible solid with a particle size 420 microns (µm) or smaller. Experimental studies indicate that fire smoke and non-fire nuisance aerosols (dust) can be distinguished by a boundary of about 1 µm.

Solo aerosol smoke testers (such as Solo A10/A10S) produce synthetic smoke particles with a size range of 0.2 to 0.3 microns (µm). This specific size range is designed to simulate the scattering characteristics of smoke from real fires and ensures compatibility with both optical (photoelectric) and ionization smoke detectors.

The idea was that the gas would enter the alarm system, and alter an electrical current inside, thereby setting off the alarm.

·        Any non-sprinklered building

·        Any non-sprinklered room

·        Non-sprinklered electrical or telecommunication rooms

·        Smoke detectors for fire doors that are held open

·        Smoke detectors for fire dampers that require a smoke detector signal to close

·        Air handing units that exceed 2000CFM or 15000CFM.

·        Alarm control equipment in unattended locations

·        Elevator lobbies, elevator machines, or hoistways (code permitting)

·        Day cares, specifically with kids under the age of 5 years

·        Pre-action or deluge applications, cross zoning

·        Atriums and surrounding areas for smoke purge applications

And of course, residential applications such as multi-family living, hotel, independent living, dormitory, and others will always require smoke alarms in all sleeping rooms and within 15 feet of the bedroom doors.

So, at a minimum, these locations generally will require smoke detection.

In review of the NFPA 72 document, 72 does allow for additional smoke detection if a building owner chooses to add additional smoke detectors. Remember that building codes are a minimum and a building owner or designer may request additional smoke detection if desired. NFPA 72 17.5.3.3.1. titled Nonrequired Coverage does discuss and allow for this request. However, there must be reason in the submitted design that documents the objective for additional smoke detection coverage.

Why would a building owner or designer request smoke detection when it is not required by the code?

1.  Smoke detectors offer early warning. A smoke detector is a fast responding sensor in comparison to heat detection used with sprinkler heads. Often with the use of early warning devices a possible disaster can be adverted to a minor incident with minimal damage or disruption.

2.  Smoke detectors are your eyes and noise when you are not around. We all have those areas of the building that are infrequently visited. Unattended locations can lead to fast growing fires and lead to unmanageable circumstances. A smoke detector can monitor that area that is infrequently visited.

3.  The smallest fire can contaminate and damage valuable contents such as computers, networks, vintage collectables, furniture, food, fabrics, paper goods, money, medicine, and other soft materials that spoil, absorb smoke and burn quickly.

4.  A small fire can lead to lost business opportunities, operations, future revenue, lost customers, inventory, and your personal income.

5.  A building fire can lead to possible injuries, fatalities and law suits. These events can also lead to negative publicity and a negative corporate image suggesting that public safety was disregarded.

6.  Avoiding sprinkler system activation. At times water can be damaging to the building and its contents. An owner may want to achieve early warning and eliminate the threat of fire prior to the activation of the sprinkler system.

7.  Early warning is being “GREEN”. Early warning avoids use of water, fire trucks, fuel, emergency resources, energy, service vehicles, loss of heat, cooling, productivity, time, garbage, displacement, carbon emissions, or reconstruction.

8.  Peace of mind and protecting life. Your place of business is safe and under constant supervision.

9.  Early warning and needed time for personal to help occupants who are not self-preserving such as the elderly, the hospitalized, institutionalized, the sick, infants and the incapacitated.
Safety for first responders. Attending to fire in its earliest incipient stages is less threatening than a fully involved fire with toxic gases, extreme heat and a weakened building structure.

10.              Perhaps you are a survivor of a fire and have firsthand experience of the danger from a fire. You understand the dangers and the severity a fire can bring. Fire burns and fire gases can kill. Smoke detectors do save lives. Ask for smoke detection if you want it and value their life safety capabilities.

11.              Redundant detection. A smoke detection system is not subject to inoperable conditions due to a lack of water, a broken sprinkler pipe, frozen pipe, a shut control value, or a broken water flow switch. Smoke detection is a distributed system with redundancy and can serve as a second backup to a by passed sprinkler system.

12.              Intentional arson concerns. Just like a video camera, a smoke detector can be a deterrent not to initiate a fire. Whether it is a disgruntled employee, family member, tenant, carelessness, terrorist act or vandalism, it is the real world. Society is unpredictable and designers should be applying some thought to the unforeseen. If the intent to harm is premediated and an individual has some understanding of fire protection concepts, one can cause great harm with the use of fire. However, with a fully smoke protected building an arson act may be deterred.

 

In summary, smoke detectors are fast responding fire alarm sensors that can summon first responders quickly when seconds count.