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A type of incinerator that provides for a controlled combustion process, with the purpose of reducing human remains to carbon dioxide, water vapor, other gases, and small noncombustible residues that are further processed in an environmentally acceptable manner.



  1. Oxygen
  2. Heat
  3. Fuel - most commonly fossil fuel, it reacts with oxygen to produce heat.

3 Things (In right Proportions) Needed for Combustion


The resulting chemical reaction of oxygen, heat, and fuel: it cannot start or continue if one of the three elements is not present or is removed. Occurs when a combustible material, in combination with a sufficient quantity of oxygen, is exposed to an external ignition source (heat or ambient temperature) above te flash point for the fuel and oxidizer mix.

  • Heat- a form of energy
  • Oxygen- most common oxidizer
  • Fuel- most commonly hydrocarbon based



A chemical process where molecules rearrange themselves, either releasing or absorbing energy.



Must be able to sustain a rate of rapid oxidation that produces a self-sustaining, exothermic chemical chain reaction.

  • Resulting reaction continues without the need for an additional external ignition source, and continues until all the available fuel is consumed, removed or the temperature reduced by cooling.

Chemical Reaction


A process that releases energy in the form of heat



A rapid oxidation process, in which hydrocarbons react with oxygen, releasing a great deal of heat and light in the process.



Results when the heat does not dissipate faster than it is created. In an incinerator, the objectives of this are the complete destruction of the organic constituents to form harmless gases and preventing the release of any harmful materials into the atmosphere.

  • Complete
  • Stoichiometric
  • Perfect



  • Carbon dioxide (CO2)
  • Water (H2O) vapor

Products of Combustion


Theoretical point at which the ratio of fuel to oxygen results in this.

Complete Combustion


When all the carbon in the fuel forms CO2 and all the hydrogen forms H2O.

Stoichiometric Combustion


When all the fuel and all the oxygen are totally consumed.

  • Can only occur in a controlled lab environment

Perfect Combustion


Operate as closely as possible to stoichiometric combustion to maximize efficiency and the reduction of environmentally harmful emissions that are the products of incomplete combustion.

Goal of All Combustion Processes


Occurs when complete oxidation of the combustible material does not occur (i.e. the combustible does not unite with the maximum amount of oxygen).

  • When lack of oxygen results in one carbon atom uniting with only one atom of oxygen, carbon monoxide (CO) forms instead of carbon dioxide.
  • Oxygen insufficiency can also result in the production of smoke, the visible suspension of carbon or other particles in the air emitted during the process.

Incomplete Combustion


Amount of air that must be added to make certain all energy is retrieved.

  • Combustion process must be adjusted so the proper amount is present.
  • Level is set based on variables such as type of fuel supply (fuel+cremation container+remains), changes in atmospheric pressure, and other factors.

Excess Air


From the ignition source to the adjacent layer of gas mixture.

  • Each point of the burning layer serves as ignition for the next adjacent layer, and so forth.

Spread of Combustion


When total heat energies of the reactants and the total heat energies of the products reach equilibrium.

End of Combustion


The substances that take part in and undergo change during a chemical reaction.



Obtain optimal efficiency is ensured by proper ratio and distribution of the fuel and the oxidant in the incinerator, by regulating the conditions for heat transfer from the combustion products, and by appropriate aerodynamics of gas flow in the device.

  • To a certain extent, radiation contributes to the heat exchange.

Control of the Combustion Process


The transfer of heat in the form of waves or rays through space.



Equipment used to accomplish the reduction of combustible material by direct combustion through a sequence of steps.

  • Primary process- drying during the initial heating of the combustible material to drive off moisture, volatilization of the vapors and gases which occur as the temperature of the material raises, combustion of the change, and burnout of the solids.
  • Secondary process- Combustion of the vapors, gases, and particulates driven off during the primary process.



Portable, packaged, completely assembled direct-fed incinerators

  • Suitable for type 2 waste
  • 25 lbs/hr burning capacity

Class I Incinerator


Portable, packaged or job assembled direct-fed incinerators.

  • Type 3 waste
  • 25 lbs/hr up to but not including 75/hr burning rate

Class IA Incinerator


Flue-fed, single chamber incinerators.

  • Type 2 waste

Class II Incinerator


  • Chute fed
  • Multiple chambers
  • Type 1, non-industrial or Type 2 waste

Class IIA Incinerator


Direct-fed incinerators

  • Type o, Type 1, or Type 2 waste
  • 100 lbs/hr or over burning rate

Class III Incinerator


Direct-fed incinerators

  • Type 3 waste
  • 75 lbs/hr or over burning rate

Class IV Incinerators


Municipal incinerators 

  • Type 0, type 1. type 2, or type 3 wastes or a combination of all four wastes
  • Rated in tons/hr/24 hrs.

Class V Incinerators


Crematory and pathological incinerators.

  • Type 4 waste

Class VI Incinerators


Incinerators designed for specific by-product wastes

  • Type 5 or 6

Class VII Incinerators


Municipal sewage sludge incinerators

  • Type 7 waste

Class VIII Incinerators



  • Mixture of combustible waste from commercial and industrial activities
  • Paper, cardboard, wood, boxes, and combustible floor sweepings containing up to 10-20% petrochemical waste (plastic), 5% noncombustibles, and 10% moisture by weight
  • Average heating value 8,500-9,500 BTU/lb

Type 0 Waste


The amount of heat.

Heating Value



  • Mixture of combustible waste from commercial and industrial activities
  • Paper, cardboard, wood scrap, foliage, floor sweepings containing up to 10% petrochemical waste, 5% non-combustibles, and 10% moisture by weight.
  • Average heating value 6,500-7,000 BTU/lb

Type 1 Waste



  • Evenly distributed mixture of rubbish and garbage as usually received in municipal waste (residential sources)
  • Contain up to 7% noncombustible solids, 50% moisture content by weight.
  • Average heating value= 4,300-5,000 BTU/lb.

Type 2 Waste



  • Animal and vegetable wastes from restaurants, cafeterias, hotels, clubs, institutions, markets, and similar installations containing up to 5% non-combustible solids and 70% moisture content by weight.
  • Average heating value= 2,500- 3,500 BTU/lb

Type 3 Waste



  • 100% human and animal tissue, organs, and solid organize wastes from hospitals, laboratories, animal pounds, farms, abattoirs, etc,; containing up to 85% moisture by weight.
  • Average heat value- 1,000-2,000 BTU/lb

Type 4 Waste


Industrial process wastes

  • Gaseous, liquid, or semi-liquid wastes
  • Composition, heating value, moisture content and ash content are variable or unknown and must be confirmed by a waste analysist.
  • BTU heat value varies

Type 5 Waste


  • Semi-solid and solid combustible wastes which require hearth, retort or grate burning equipment.
  • Combustion, heating value, moisture content, and ash content are variable or unknown
  • BTU heat value varies

Type 6 Waste


Municiple Sewage Sludge Waste

  • Consists of residue generated from the processing of raw sludge from a treatment plant

Type 7 Waste


  • Minicipal solid waste
  • Medical/infectious waste (other than pathological waste)
  • Radioactive waste
  • Hazardous waste
  • fiberglass and plastic containers
  • Narcotics

Items typically not allowed to be incinerated


  1. Controlled air incinerators
  2. Rotary kiln incinerators
  3. Multiple-chamber/excess-air incinerators (cremators)

Types of Incinerators:


Multiple-chambered retors that are specifically designed for the incineration of human remains.



  1. In-line hearth
  2. Retort hearth

Two Kinds of Multi-Chamber Designs


Combustion gases flow vertically only.

In-line Hearth


Additionally directs the flow of combustion gases "sideways" through a secondary chamber adjacent to the primary combustion chamber.

  • The most efficient design for capacities less than 750lb/hr

Retort Hearth


What crematory retorts are sometimes referred as:

  • Excess or ambient air is used to ensure complete combustion during the cremation process.

Excess air retorts


Mostly used for medical waste incineration.

  • Starved air incineration- waste is fed into a primary or lower combustion chamber operating at less than the amount of air required for combustion: air enters the chamber below the incinerator hearth (underfire air).
  • Excess air is added to the volatile gases formed in the primary chamber to complete combustion.

Controlled Air Incinerators


Also designed with a primary chamber, a horizontal rotating kiln to heat and volatize the waste, and a secondary chamber to complete combustion of the combustion gases passed from the primary chamber.

  • Treatment of liquid and solid hazardous waste
  • May or may not operate with excess air.

Rotary Kiln Incinerators


  • Case (charge) - container or body is placed in primary combustion/incineration chamber.
  • Loading (charge) door is closed and locked (can be performed after preheating).
  • Afterburner is first ignited to bring secondary chamber to target temperature.
  • When target temperature is reached, primary burner chamber ignites.
  • Case is dried, ignited, and combusted by the heat provided by the primary chamber burner, as well as by radiant heat from refractory walls.
  • Moisture and volatile components in the material are vaporized and passed out of the primary chamber through a flame port which connects the primary chamber to the secondary chamber, along with combustion gases.
  • Secondary (excess) air is added through the flame port and mixed with volatile contents in secondary chamber (mixing chamber between the primary and secondary chamber).
  • Burners in the secondary chamber must be maintained at adequate temperatures for combustion of volatile gases.
  • Gases exiting the secondary chamber are directed to the cremator stack.
  • When the waste is driven off or consumed, the primary burner shuts off.
  • Typically the afterburner shuts off after a set time.
  • Once the chamber cools, the cremated remains are removed from the primary chamber floor and a new case can be added, in accordance with manufacturer instructions.

Basic Multi-Chamber Incinerator Process


  1. Time
  2. Temperature
  3. Turbulence

Three Main Factors Affecting Cremation Combustion Process


The length of time needed to consume or drive off products of combustion during the cremation process.

  • Essential to be given enough retention time in the afterburner chamber and primary cremation chamber to be consumed, so that they are not released into the atmosphere.



The average time for gasses to pass through a chamber.

Retention Time (Residence Time)


  • Critically important
  • Proper range between 1,400 and 1,800 degrees F.
  • Some states require secondary chamber must remain at 1,800 degrees F because if the temperature falls below 1,400 degrees F it may not be possible to completely incinerate a container or any other products of combustion.
  • When exceeds 1,800 degrees F- Combustion products move through the afterchamber too quickly.
  • Either scenerio could produce emissions



If effective, increases combustion efficiency. Created in the cremator's exhaust system by having the gases change directions through perforated walls and baffle systems.

  • Helps gases properly mix, driving off and consuming and products of combustion before relase into the atmosphere.



  • Electronic controls
  • Hearth
  • Refractory brick
  • Burners
  • Primary chamber
  • Secondary chamber
  • Stack
  • Clearance

Basic Multiple Chamber Cremator Structure


Allow operator to monitor and adjust the internal environment of the cremator.

Electronic Controls


The "floor" of the cremation unit.



Made to withstand high temperatures. 

  • lines the inside of the cremator.

Refractory Brick



Positioned above the body in the primary chamber and are the primary source of heat during the cremation source.


Where the cremation takes place. The heat and air are mixed here, creating combustion.

Primary Chamber


Holds the unburned combustion materials from the primary chamber until complete combustion is achieved, and allows for proper and controlled air flow to the stack.

Secondary Chamber


The final discharge point where the products of combustion are released into the environment.



The stack must have proper ______ from any combustible materials present in the ceiling or roof structure, including proper clearance from any insulation that may be present.



  • Flow gases from front to back, then out.
  • Does not recirculate exhaust underneath the hearth.
  • Units usually longer and narrower

In-Line Cremator Design


  • Air flow from front to back, then underneath hearth.
  • Units usually taller and wider.

Retort Design


  • Refractory material is non-metallic and heat-resistant.
  • Chambers are interconnected by gas passage ducts or ports, designed to provide for complete combustion of the material to be burned.
  • Incinerators designed to routinely achieve the complete burning of combustion gases leaving the primary combustion chamber, through control of temp and exhause gas flow rate.
  • Practically all new equipment has systems that control the air and heat (gas).
  • Older equipment- any adjustments in air should be made by the manufacturer.



Must be capable of a retention or residence time for combustion gases of at least one second at no less than 1,800 degrees F.

  • Retention time= how long the gases take to trave through the final combustion zone.

Furnace Design


Must be large enough to provide for good mixing of gases, air, and heat for thorough combustion in order to reduce the amount of particulate matter (PM) and other organc compounds in the exhaust.

Chamber (Zone)


Must be met after the combustion gases pass through the primary combustion chamber and then on through the secondary chamber.

  • Primary chambers- has burners that are directed on the container and air jets to break up the remains and promote combustion.
  • Combustion gases from the primary chamber are fed by a series of ducts into the secondary chamber and supplied with secondary air to complete and reduce emissions.



  • Temperature is maintained and regulated by the afterburner.
  • Designed for additional combustion to reduce the amount of particulates in the exhaust and minimize visible emissions.
  • Typically provides the space (required to meet a specific retention time) and temperature (provided by the afterburner) to complete the burning of hte combustion gases and further reduce particulate emission opacity.

Secondary Chamber


The burner designed to provide excess air and heat for complete combustion of the gases in the primary chamber.



Designed to provide the required combustion chamber temperatures by means of automatic modulating controls.

Auxillary Burners


  • High in moisture content and contains liquids; percentage of moisture ranges from 60-90%
  • Retorts are designed with a fixed hearth with a raised edge at the door to prevent liquids from spilling during charging.
  • Average heat value as fired of the human body is 800-3,600 BTU/lb.
  • Healthy, lean adult male- 62% water, 17% fat, 16% protein, 6% minerals, and less than 1% carbs.
  • Healthy lean woman- 22% fat, and slightly fewer other chemical components than males.

Chemical Combustion of the Human Body


  • 61% oxygen
  • 23% carbon
  • 10% hydrogen
  • 3% nitrogen
  • 1.40% calcium
  • 1.10% phosphorus
  • .20% sulfur
  • .14% sodium
  • .12% chlorine
  • .03-.003% magnesium, silicon, iron, fluorine, zinc
  • Traces- rubidium, strontium, bromine, lead, copper, aluminum, cadmium, boron, barium, tin, manganese, iodine

Average Adult Human Body


  • 47.50% phosphate (chemical compounds containing phosphorus)
  • 25.30% calcium
  • 11% sulfate (result of fossil fuel and biological material)
  • 3.69% potassium
  • 1.12% sodium
  • 1% chloride

Chemical Composition of Cremated Human Remains


  • Organic compounds
  • Nitrogen oxides
  • Sulfur dioxide
  • Carbon monoxide
  • Particulate matter
  • These are combustion products of fuel (mostly natural gas), body tissues, and containters that hold remains.
  • Emission rates dpend on the design of the incinerator, conbustion temperatures, gas retention time, hot air duct design, stack temperature, and any control devices.
  • Most states have set emission limits for particulate matter and opacity only.

Emissions: The Products of Incineration


 A complex mixture of extremely small solid particles and/or water droplets.

  • Made up of acids (nitrites and sulfates), organic chemicals, metals, soil or dust particles
  • Generated from incomplete fuel combustion of the charged remains. (Exhaust gases contain solids and liquids that did not finish burning).
  • Effectively controlled by proper equipment design and operation.

Particulate Matter (PM, Particle Pollution)


Measured as a concentration.

  • Grains in a given volume of air (cubic feet) that is emitted.
  • One pound = 7,000 grains
  • Crematories must not exceed .08 grains per dry standard cubic foot of flue gas, corrected to 7% oxygen at standard conditions.
  • Required in AZ, FL, NY, OR

Particulate Matter Measurement


The degree to which the transmission of light is reduced when viewed through a smoke plume.

  • Indication of improper combustion and excessive particulate emissions. Particulates in the atmosphere (which absorb and scatter light) obscure line of sight and reduce visibility.
  • Measured in percent opacity (testing method 5):
    • 0% means background is 100% visible through smoke.
    • 100% means that 0% background is visible

 Visible Emissions: Opacity (Exhaust Smoke)


Not connected with the crematory. This person evaluates the obscuring quality of the exhaust at specified intervals according to established viewing standards, usually every 15 seconds for 3 hours.

  • EPA Method 9- Visual opacity

Certified Observer


Equipped on stacks, give the operator the ability to quickly make adjustments to control exhaust without having to do a visual check outside of the facility. Types:

  • Transmissometers (most common)
  • If no unit- must measure by eye

Opacity Monitors


Mounted on either side of the stack. A beam of light is projected from one side through the exhaust flow and detected by a sensor.

  • If projected light is obstructed, energy of the light is reduced, percent opacity is then determined by comparing the energy levels to that of the projected light.



Too high of a temperature causing the exhaust gas to pass through the combustion zone too quickly and unevenly

  • high fuel (BTU) value- polished wood caskets or alarge decedents

Excessive Smoke


  • Protocol provided to the state, subject to regulatory approval
  • A reason to suspect that particulate emission limits are not being met
    • age of cremator
    • frequent opacity limit violations
    • Complaint by someone in community

Testing Emissions


  • Wet Scrubbers
  • Baghouse/Fabric filtration

Add-on Pollution Control Devices


 Devices used to trap suspended particles by direct contact with a spray of water or another liquid.

  • Washes particulates (fly ash, odorous compounds) out of the airstream as they are carried along by droplets in the spray.
  • Control odors from pollutants (hydrogen sulfide, other sulfur compounds)
  • Not commonly used in the US- high cost

Wet Scrubbers (Flue Gas Washers)


Basically a dust collection system. Removes suspended particles using an assembly of fabric-filler bags (baghouse).

  • Dust laden air is blown upward by fans that trap the particulates inside, while clean air passes through and exits at the top.
  • Offer high resistance to air flow, leading to substantial energy use to the system.
  • Air to be cleaned must cooled before passing through the unit.
  • Used in the US, but is uncommon (high costs)

Baghouse (Fabric Filtration)