1. ISA03-P083
BURNER MANAGEMENT FLAME DETECTION
REQUIREMENTS and EXCEPTIONS
Kevin V. Maki
Engineering Manager
TransAmerican Automation Inc.
Houston, Texas 77073
KEYWORDS
BURNER MANAGEMENT SYSTEMS, NFPA, FLAME DETECTOR, FLAME
DETECTION
ABSTRACT
The use of flame detection in burner management systems has undergone some
serious changes over the years, both in the standards and codes we utilize in this
industry and the technological advancements that have been realized. While
some users continue to resist the requirements being imposed upon them, others
are embracing the new technological advances that have been made in this area
of instrumentation.
Users upgrading their systems to meet new federally mandated NOX
requirements are facing new challenges when trying to utilize their existing flame
detection systems. They are finding their older flame detectors that worked fine
before are now not working or barely working at all.
Other users are fighting serious “cost of ownership” issues when trying to outfit
their multiple burner platforms with the “required” flame detection systems. It can
get extremely expensive to outfit a 40-burner heater with flame detection on
every burner.
This paper will discuss the types of flame detectors, the buzzwords used in flame
detection, and the requirements and all-important exceptions that are part of the
current codes and standards in this field. Advances made in recent years in
flame detection will form the final portion of this paper.

2. INTRODUCTION
Flame detection is the art of applying a specific type of detector(s) based on the
type of fuel being burned, sighting and calibrating this detector(s) and providing
the control system with a repeatable and reliable means of flame on / flame off
indication. Flame strength levels can also be provided in an analog format.
There are two types of flame detection, friendly and un-friendly. Furnace burner
management utilizes a friendly fire detector. The unfriendly fire detectors are
used in the fire and gas industry. Flame detectors for furnaces are designed to
sense a stable flame that will support continued combustion. Flame detectors for
the fire and gas industry are designed to detect “any” flame.
A flame detector is typically composed of a viewing head that houses the
photocell detector and electronics and an amplifier unit that provides signal
strength and form C contact outputs. Adjustments to gain settings and filters can
be found on either the viewing head or the amplifier, depending on the
manufacturer.
Some of the questions that this paper will answer are:
What is Flame Detection and how does it apply to Burner Management?
What is “flame failure response time”?
What is “self checking”?
What are the different flame detection methods?
What are the traditional driving factors in the selection of a flame detection
system?
What standards and codes are available for guidance in this endeavor?
What advances have been made in the field of flame detection?
To better understand the requirements, as they exist today, we first need to
explore and define some terminology that is being used in this field.

3. DEFINITION OF TERMS
ELECTROMAGNETIC SPECTRUM
The full range of frequencies, from radio waves to gamma rays, that
characterizes light. The light that flame detectors work with is in the middle of the
spectrum, between microwaves and X-rays.
FLAME
The visible or other physical evidence of the chemical process of rapidly
converting fuel and air into products of combustion.
FLAME DETECTOR
A device that senses the presence or absence of flame and provides a usable
signal for control purposes.
LOW NOX
The classification of a type of burner that produces limited amounts of nitrous
oxide when fuel and air are burned at the ratios recommended by the burner
manufacturer.
DISCRIMINATION
This is the flame detector’s ability to differentiate between adjacent flames and /
or light sources. A detector with poor discrimination will sense the flame of
adjacent flames or glowing refractory, which is known as crosstalk.
SIGNAL LEVEL
The level of signal that a flame detector provides, indicating the strength of a
particular flame. A poor signal level will result in nuisance trips of the burner.
FLAME FAILURE RESPONSE TIME (FFRS)
The “flame failure response time” is the time delay between the occurrence of a
“flame off” condition and the activation or de-activation of the “flame on” signal
contact output. This provides a slight time delay to allow for momentary losses of
the flame signal and helps to prevent nuisance trips of the burner.
Typically, this time is adjustable between 1 to 4 seconds. The industry standards
and insurance codes usually limit this setting to a maximum of 4 seconds.

4. SELF CHECKING
There are two basic forms of diagnostic checking that a detector uses to prove
that it is operating correctly and not indicating a false flame. Electronic self-
checking utilizes manufacturer specific electronic circuitry to monitor the pulses
from a detector and / or current levels of the signal to prove that the detector is
not in a runaway condition. Electronic self-checking is normally done in the
amplifier section of the system.
Mechanical self-checking (shutter based) is also used on detectors. A
mechanical shutter is placed in the path of the light being measured and the
detector amplifier diagnoses the loss of the signal to prove the detector is not in a
runaway condition. Shutters can be anything from sliding gate to rotary type, as
long as it blocks the path of light to the photocell. Mechanical self-checking has
to be done in the viewing head section of the system. For this reason, these
viewing heads are typically more susceptible to vibration damage.
ELECTROMAGNETIC SPECTRUM
Flame detectors work by sensing light from the electromagnetic spectrum,
usually in the ultraviolet and infrared portions.
The combustion of fuel in a furnace produces a resultant light emission in the
ultraviolet portion of the spectrum (10 – 400 nanometers). Light in the UV
spectrum has a shorter wavelength and a stronger level of energy.
The presence of a flame due to the combustion of the fuel and air mixture also
produces a resultant light in the infrared portion of the spectrum (700 – 10,000
nanometers). Light in the infrared spectrum has a longer wavelength and a lower
level of energy.
Wavelength (m) Frequency (Hz) Energy (J)
Radio > 1 x 10-1
< 3 x 109
< 2 x 10-24
Microwave 1 x 10-3
- 1 x 10-1
3 x 109
- 3 x 1011
2 x 10-24
- 2 x 10-22
Infrared 7 x 10-7
- 1 x 10-3
3 x 1011
- 4 x 1014
2 x 10-22
- 3 x 10-19
Optical 4 x 10-7
- 7 x 10-7
4 x 1014
- 7.5 x 1014
3 x 10-19
- 5 x 10-19
UV 1 x 10-8
- 4 x 10-7
7.5 x 1014
- 3 x 1016
5 x 10-19
- 2 x 10-17
X-ray 1 x 10-11
– 1 x 10-8
3 x 1016
- 3 x 1019
2 x 10-17
- 2 x 10-14
Gamma-ray < 1 x 10-11
> 3 x 1019
> 2 x 10-14

5. FLAME DETECTION METHODS
FLAME ROD
A metal rod, insulated by a ceramic material, that extends into the flame itself.
When the flame envelope touches the rod, rectified current flows from the
amplifier through the rod, into the flame and back to burner ground. At a
predetermined level of current, a relay contact in the amplifier unit closes and
signals the presence of flame. This is a very simple, inexpensive system but it
resides within the harsh environment of the furnace and requires a high level of
maintenance to keep the system operating reliably.
ULTRAVIOLET (UV)
A vacuum tube (UV) photocell based detector that responds to the ultraviolet light
spectrum of 180 - 200 nm, which is the usual range of combustion and not
radiant heat. This is a very effective system, is inexpensive and easy to
implement. It is however, affected by water vapors and certain chemicals, which
tend to block or weaken the signal strength.
OPTICAL (OP)
A silicon (Si) photocell based detector that responds to the visible light spectrum
of 400 – 700 nm. This method is not widely used due to its limitations with any
form of light the human can visually see.
INFRARED (IR)
A germanium (Ge) photocell based detector that responds to the infrared light
spectrum of 750 – 1900 nm. This detector is very useful on oil burners where the
UV signal is not as strong by detecting the presence of infrared light. Glowing
refractory walls and boiler water tubes also produce infrared light, which can be a
problem with maintaining the required level of discrimination in a multi burner
application.
IR FLICKER
A lead sulfide (PbS) photocell based detector that responds to the infrared light
spectrum of 1000 – 3000 nm. It operates in the range of 0 – 2000 Hz and detects
the flicker frequency of the flame. A quality detector will operate at the upper
ranges of this frequency and damp the lower range, providing excellent
discrimination between adjacent flames and glowing refractory.

6. UV / IR
A combination of ultraviolet and germanium photocells are used in this detector,
usually with adjustable gain settings and filter settings for each photocell. This
allows for the ultimate in flame sensing and the ability to tune the detector to
almost any operating condition. Most detectors of this type come with user
configurable switching that allows you to utilize one photocell over another.

7. DETECTOR SELECTION TABLE
The following table shows the various detector models and how they typically
respond to certain fuels. The values range as follows; None, Poor, Fair, Good,
Excellent.
Burner Fuel Type of Photocell Signal Level Discrimination
Natural Gas
Hydrogen
Propane
UV
Ultraviolet
Good Excellent
PbS (lead sulfide)
IR Flicker
Good Good
Si (Silicon)
Optical
None None
Ge (Germanium)
Infrared
Good Fair
UV / IR Excellent Excellent
Heavy Oil
UV
Ultraviolet
Poor Excellent
PbS (lead sulfide)
IR Flicker
Good Good
Si (Silicon)
Optical
Very Good Poor
Ge (Germanium)
Infrared
Very Good Fair
UV / IR Excellent Excellent
Pulverized Coal
UV
Ultraviolet
Poor Excellent
PbS (lead sulfide)
IR Flicker
Good Good
Si (Silicon)
Optical
Good Fair
Ge (Germanium)
Infrared
Very Good Poor
UV / IR Very Good Excellent
Low Nox
UV
Ultraviolet
Fair Fair
PbS (lead sulfide)
IR Flicker
Good Good
Si (Silicon)
Optical
None None
Ge (Germanium)
Infrared
Fair None
UV / IR Good Good

8. DEFINITION OF TERMS
ELECTROMAGNETIC SPECTRUM
The full range of frequencies, from radio waves to gamma rays, that
characterizes light. The light that flame detectors work with is in the middle of the
spectrum, between microwaves and X-rays.
FLAME
The visible or other physical evidence of the chemical process of rapidly
converting fuel and air into products of combustion.
FLAME DETECTOR
A device that senses the presence or absence of flame and provides a usable
signal for control purposes.
LOW NOX
The classification of a type of burner that produces limited amounts of nitrous
oxide when fuel and air are burned at the ratios recommended by the burner
manufacturer.
DISCRIMINATION
This is the flame detector’s ability to differentiate between adjacent flames and /
or light sources. A detector with poor discrimination will sense the flame of
adjacent flames or glowing refractory, which is known as crosstalk.
SIGNAL LEVEL
The level of signal that a flame detector provides, indicating the strength of a
particular flame. A poor signal level will result in nuisance trips of the burner.
FLAME FAILURE RESPONSE TIME (FFRS)
The “flame failure response time” is the time delay between the occurrence of a
“flame off” condition and the activation or de-activation of the “flame on” signal
contact output. This provides a slight time delay to allow for momentary losses of
the flame signal and helps to prevent nuisance trips of the burner.
Typically, this time is adjustable between 1 to 4 seconds. The industry standards
and insurance codes usually limit this setting to a maximum of 4 seconds.

9. used. This validation shall not be used to replace unit acceptance tests relating to
proof of design, function and components.
NFPA 86 STANDARD FOR OVENS AND FURNACES 1999 EDITION
NFPA 86 applies to all class A and B ovens, dryers and furnaces. Specifically,
any oven or furnace that operates at approximately atmospheric pressure and is
used for the industrial or commercial processing of materials. This standard is
much like the boiler standard but does have some exceptions that can be very
important in the initial design of the furnace.
Some of the more important requirements and exceptions are outlined below.
Section 5-9.1 Each burner flame shall be supervised by a combustion safeguard
having a maximum flame failure response time of 4 seconds or less, that
performs a safe-start check, and is interlocked into the combustion safety
circuitry.
Exception No. 1: The flame supervision shall be permitted to be switched out of
the combustion safety circuitry for a furnace zone when that zone temperature is
at or above 1400 Deg F (760 Deg C). When the zone temperature drops below
1400 Deg F (760 Deg C), the burner shall be interlocked to allow its operation
only if flame supervision has been re-established.
Exception No. 2: Combustion safeguards on radiant tube-type heating systems
shall be required where a suitable means of ignition is provided and the systems
are arranged and designed such that the following conditions of (a) or (b) are
satisfied.
(a) The tubes are of metal construction and open at one or both ends with
heat recovery systems, if used, and they are of explosion proof
construction.
(b) The entire radiant tube heating system, including any associated heat
recovery system, is of explosion-resistant construction.
Exception No. 3: Burners without flame supervision shall be permitted, provided
these burners are interlocked to prevent their operation when the zone
temperature is less than 1400 Deg F (760 Deg C). A 1400 Deg F (760 Deg C)
bypass controller shall be used for this purpose.
Section 5-9.2.2 Line burners, pipe burners, and radiant burners, where installed
immediately adjacent to one another or connected with suitable flame-
propagating devices, shall be considered to be a single burner and shall have at
least one flame safeguard installed to sense burner flame at the end of the
assembly farthest from the source of ignition.

10. By utilizing the exceptions above into the initial heater design, control system
costs can be greatly reduced while significantly enhancing the safety of the
furnace.
API RP 556 Instrumentation and Controls for Fired Heaters and Steam
Generators 1997 Edition
This is a recommended practice that was put together by the American
Petroleum Institute. It applies to fired heaters and steam generators in the
petroleum refinery and other hydrocarbon processing plants.
The recommendations in this practice to minimize flame failure are a reliable fuel
system, reliable pilots and reliable burner pressure control. In the instance one of
these cannot be provided, then flame monitoring is recommended. There are
several paragraphs on the types of flame detector to use, self-checking over non
self-checking, etc.
FLAME DETECTION ADVANCES
Special coatings
Advances in optical coatings are giving detector manufacturers additional
methods of filtering out unwanted portions of the spectrum while concentrating on
the spectrum where the highest energy is available.
Packaging
Advances made in the field of electronics over the years has led to smaller and
smaller packages for flame detection. This has lowered the cost of panel space
and the price of the units themselves. A quality flame detector loop can easily be
purchased and installed for well under a $1,000 per loop.
Advances in viewing head design are also being made such that the viewing
heads are much smaller, have built in quick connect fittings and some are even
rated for Nema 7 (Class I, Div II) operation without utilizing the expensive and
bulky cast aluminum canisters of previous models.
Smart Detectors
Calibrating detectors has always been a tricky prospect. Today’s detectors make
that process much easier with the use of RISC based technology in the viewing
heads and amplifiers.
Many detectors today are smart detectors. They can be taught a specific flame
profile within an installation and then respond reliably to that profile in abnormal

11. circumstances. Calibration consists of teaching the detector “flame off” and
“flame on” conditions in a cold furnace and then doing the same in a hot furnace.
Fiber Optics
In the case of excessively high heat (incinerators), high vibration (lime kiln feed
shakers), tilting burners (black liquor boilers) and / or the presence of highly
corrosive chemicals (waste incinerators), the use of fiber optics to extend the
viewing head distance can be used. A metal clad fiber optic cable is used to
extend the viewing head distance by as much as 40 feet, enabling the viewing
head and delicate electronics to be located in a much friendlier environment.
CONCLUSION
For many years, engineers and technicians have referred to “flame detection” as
a black art. This was because very little effort went into the selection of the
detector and / or it was improperly installed, leaving the operators and field
technicians no choice but to bad mouth the technology.
While it is easy to let someone else do the “flame detection”, it is actually very
simple to incorporate. Once you know the characteristics of the fuel you are
burning and the types of the detectors that respond to those characteristics, the
rest is no harder than specifying a basic process instrument.
Cost was another factor in flame detection, in the past a flame detection loop
could cost as much as $5,000 to purchase and install.
With the advances made to date, a simple UV loop can be purchased and
installed for under a $1,000. That is a small price to pay for increased safety in
any environment.