Monday, July 31, 2017

NFPA 72 2010 Code Book Secrets

Well the title says secrets but to be honest it really is public information.  However not too many readers are aware of it.  Check this out.  The 2010 edition of NFPA 72 National Fire Alarm and Signaling Code has a few items throughout the text that can help the readers better understand the changes and new layout.

    NFPA 72 2010 Margins for New Content
  • A vertical bar in the margin indicates that a change other than editorial has been made.
  • A bullet indicates that one or more complete paragraphs have been deleted.
  • A reference in parenthesis () following a paragraph indicates technical committee responsibility.
  • A reference in brackets [] indicates exacted material from another document.

If you are interested in taking the NICET Test for "fire alarms" or "Inspection and Testing of Fire Alarms", then we have you covered!  We are now selling our CBT Levels 1 - 4 NICET practice test with preparation material.  This material is packed with tons of NICET practice test questions along with all code references as to where to find the answers.  We have also supplied the material with all of the necessary NICET applications, CBT calculator demonstrations, links and more.  If you need more information, feel free to send an email.  You can find the link to purchase our NICET Practice Test on the top left section of this site.

Monday, July 24, 2017

Fire Alarm Calculations

If you are preparing to take the NICET exam for Fire Alarm Systems, there are numerous fire alarm calculations you must understand in order to properly design a code compliant system.  These calculations can break down exact requirements for sound pressure (dB) levels, voice intelligibility, voltage drop on a circuit, back up battery sizes, candela settings and dB line loss for speaker circuits.  There are additional calculations however these are some of the most common and important so this article will concentrate on the following:

You can also download our Fire Alarm Calculation Tool here.


How to find the correct Candela Strobe to cover a given space


This is a very important measurement as it allows us to properly calculate the necessary candela power needed for a given space.  If you do not have NFPA 72 2013 edition tables 18.5.5.4.1(a) and 18.5.4.4.1(b) handy or memorized, this formula will save the day!

Take the selected candela (ex. 75 cd) and divide it by 0.0375
75 cd / 0.0375 = 2000
Now take the square root of 2000 to get a spacing of = 44.72136 feet.

If you consult NFPA 72 2013 tables 18.5.5.4.1(a) it shows a spacing of 45 x 45 feet and table 18.5.5.4.1(b) shows a spacing of 44 x 44 feet.

Voltage Drop Calculation


Step #1:  Find the total current from all of your field notification appliances.  If you consult the appliance's specification sheet, you will find the current draw for each setting.  For example, you have four appliances on the temporal high setting and they each draw 50mA or (0.050A).  If you add all four appliances together (4 x 0.050) you have a total current draw of   0.2A

Step #2:  Determine the to and from distance of the notification appliance circuit (NAC).  For this example, we will saw the NAC is 450 feet.  We have to double this distance to account for both conductors.  450 feet x 2  = 900 feet.

Step #3:  Now that we know the distance, we need to know what type of conductor we are using for the circuit.  For this example we will use a #12 AWG solid coated copper conductor.  Once this is determined, we will need to consult the Conductor Properties table 8 in the National Electrical Code or NEC 2011 (click the link to view a copy of the table).  This table can also be found in chapter 9 on page 721.   On the table, located the section at the top under coated.  Now follow the line down under ohm/kFT (ohms per 1000 feet).  Keep scrolling down until you reach the 12 AWG with a quantity of 1 since it is solid.  If you line the left and top rows up, you will see a resistance of 2.01 ohms for 1000 feet of conductor.

Step #4:  Since we do not have a distance of 1000 feet for a out circuit, we will need to break down this resistance according to our actual distance of 900 feet.  To do this simply divide 900 feet by 1000 feet sown as 900/1000 = 0.9.  Now multiply your resistance per 1000 feet (2.01) by your distance breakdown of 0.9.  2.01 X 0.9 = 1.809 ohms per 900 feet.

Step #5:  To determine the voltage at the end of the notification appliance circuit we need to use Ohm's Law.  Since we know know the total amps (0.2A) and the total resistance (1.809) we can now find the voltage.  I X R = E or Amps x Resistance = Voltage.  0.2 x 1.809 = 0.3618 volts.

Step #6:  To find the voltage drop subtract your answer found in step #5 (0.3618) from the starting voltage of 24 volts.  24 - 0.3618 = 23.6382 volts.

Step #7:  Sometimes you may be asked to know the voltage drop percentage.  To find this, take the voltage drop (0.3618 volts) divided by 24 volts and multiply it by 100.  This is shown as (0.3618/24) x 100 = 1.5075%

See more examples of voltage drop for NACs here

Resistor Calculations


Calculating Resistors in Series


If you come across multiple resistors in series with each other, simply add the resistor values.

Resistors in series for fire alarm circuit
Resistors in Series
Example:
R1 = 3.3k
R2 = 4.7k
R3 = 10k
Total Resistance = 18k

Calculating Resistors in Parallel 

fire alarm resistors in parallel
Resistors in Parallel

1/Rt = 1/R1 + 1/R2 + 1/R3

R1 = 200
R2 = 400
R3 = 800

1/Rt = 1/200 + 1/400 + 1/800

If there is a common denominator for the bottom numbers use it by multiplying up both the top and bottom numbers in the fraction.

Example: the common denominator is 800.

Resistor R1 has a resistance of 200.  200 goes into 800 4 times.  Therefore R1 = 4/800
Resistor R2 has a resistance of 400.  400 goes into 800 2 times.  Therefore R2 = 2/800
Resistor R2 has a resistance of 800.  800 goes into 800 1 times.  Therefore R3 = 1/800

Now add the top numbers together (4 + 2 + 1 = 7) and place it on top of 800 like this 7/800.  Now take the reciprocal to make the fraction reverse to 800/7.  Divide 800 by 7 to get your answer of  = 114.286k.

Battery Calculations


Take the total standby current and multiply by 24 (hours for standby)
Take the total alarm current and multiply by (.083 for 5 minutes or .249 for 15 minutes of alarm)
Add the total of (standby current x 24) to (alarm current x .083 or .249)
Multiply the total of above by a safety factor of 1.2.  This gives you a 20% spare buffer.
Round up to required battery amp hour size.

dB Loss and Gain


Every time you double the distance from the audible appliance, you loose 6 dB.

Example:  If you have a speaker with 75dB at 10 feet, you will have 69dB at 20 feet and 63dB at 40 feet and so on at 80 feet, 160 feet......  Please note, these are not multiples of 10 feet!!!  These are broken down by doubling the distance from the last measurement.
Correct: 10 feet - 20 feet - 40 feet - 80 feet - 160 feet
Incorrect:  10 feet - 20 feet - 30 feet - 40 feet - 50 feet - 60 feet

If you double the power output of the appliance, you gain 3dB.

Example:  If you have a speaker tapped at a 1/4 watt with 75dB and you double the wattage to 1/2 watt, you will then have 78dB.


dB Line Loss Calculation


TLR = Total Load Resistance
TWR = Total Wire Resistance
TWR = Ohms/Foot X (Distance X 2)

12 AWG Ohm/FT is .00193
14 AWG Ohm/FT is .00307
16 AWG Ohm/FT is .00489
18 AWG Ohm/FT is .00777

TLR = (Voltage X Voltage) / Power
20 X Log (1- (TWR / TWR + TLR))

You cannot go over -1.5 dB

Wednesday, July 19, 2017

Are Your Aerosol Smoke Testers EPA Compliant

Smoke detector testing with aerosol


Seeing as smoke detector testing is a code mandated requirement to remain compliant, I will assume we all aware of aerosol smoke detector testing cans.  If not, these are the small cans of artificial smoke that utilize different types of propellants for the purpose of testing..... You guessed it, Smoke Detectors.  There is an important change on the horizon due to the EPA's "Significant New Alternatives Policy" or SNAP for short.   As of December 31, 2017, aerosol smoke detector testers that utilize HFC-134a as their propellant will no longer be manufactured.  

What do we do now?


Do not panic.  The rapidly approaching date of December 31, 2017 does not have any bearing on the physical use of smoke detector testers with the propellant HFC-134a as this is NOT a ban.  In fact the EPA has granted some manufacturers such as SDi Specialized Fire Products an UNLIMITED "sell-through" period for any and all existing stock.  The SOLO A4 Smoke Detector Tester will continue to be sold until its anticipated exhaustion date of late 2018.

Are there other products without HFC-134a available now?


The answer is yes.  For simple smoke detector tester can replacements to the Solo A4, we can recommend the three following products:

  • The Smoke Sabre Smoke Detector Tester.  This product has been available since 2009, is approved by NFPA and contains absolutely no HFC-134a making it EPA Rule 20 compliant.  This product comes in a cut above the competition as it is silicone FREE.  The lack of silicone eliminates the concern of contamination and plastic compatibility.
  •   The Smoke Centurion - This product is exactly like the Smoke Sabre, however it can be used as a hand held unit or in conjunction with the SOLO 330 aerosol dispenser.
  • HFC-134a free smoke detector tester
    SDi Smoke Centurion Aerosol Smoke Tester
  • The new SOLO A10 (from what I have heard, should be available some time September 2017).  This unit was developed in partnership with Honeywell and utilizes their Solstice ultra-low global warming potential (GWP) propellant which is also non-flammable, HFC-134a and silicone free.  This unit will be available in two convenient sizes.   

Solo 365 Smoke Detector Tester
SDi SOLO 365 Non-HFC Smoke Tester
If you are in the market for a non-aerosol smoke detector testing unit than you need to read up on the Testifire!  The first of its kind, Testifire is an electronic smoke/heat and CO detector tester.  Available in both Smoke/Heat and Smoke/Heat/CO versions, Testifire allows the user to test without aerosols using a patented smoke generation technology with no silicone.  The unit is Manufacturer approved, listed for testing, as well as NFPA and EPA Rule 20 compliant.

Another product coming very soon is the SDi SOLO 365 smoke detector tester.  This unit is used for smoke detector testing only unlike the Testifire.  The SOLO 365 utilizes the SOLO ES3 smoke cartridges providing a faster and cleaner test.    

Additional fire alarm related aerosols available through the EPA Rule 20



  • The SOLO A7 non-flammable canned air has been granted a lifetime exemption from the EPA.
  • The Smoke 400 aerosol used with the Trutest smoke sensitivity tester will continue to be available as it is not subject to the EPA Rule 20.  


In closing, make sure to inform your managers, technicians, end-users and AHJs of this important change.  As we approach the late part of 2018, these products will become increasingly harder to come by.  Make sure you stock up now or insure your company is migrating to one of the EPA Rule 20 compliant testers mentioned above.   If you have any questions or would like to discuss your experiences with these products, please feel free to join our Facebook Group.