Heat Treatment


  1. Forced Hot Air Treatment-(FHAT)


ISPM-15: ‘Guidelines for Regulating Wood Packaging Material in International Trade’ has also approved the heat treatment of Wood Packaging Material at maintaining core temperature of 56°C for 30 minutes and marked prior to export. National Standard for Forced Hot Air Treatment has been accordingly developed which describes the treatment procedure and the steps of registration of the facility. To meet the requirements of ISPM-15, it is essential to certify the forced hot air treatment facilities to ensure that wood packaging material including dunnage treated and marked in consistence with the provisions of ISPM-15.


     The minimum requirements for setting up of forced hot air treatment facility include a heat treatment chamber of appropriate capacity, which should be adequately insulated on all sides with rock/glass wool (i.e. a minimum of at least 15 cm thickness) to ensure proper thermal insulation. A heat delivery system consisting electric heaters with required heat capacity and the blowers to blow heated air into the chamber through a close ended duct with a provision to recycle the heated air and a motorized damper for exhausting 10% return air to remove moisture from the chamber after 10-15 min of the process time; a process control and interlocking system to provide adequate safety of operations; a PID single loop Temperature Controller holding a minimum of 6-8 temperature sensors connected to a paper-less temperature recorder.


The loading of chamber should not be more than 75% capacity of the chamber.


Treatment Procedure


After loading the pallets into the chamber, the door should be closed before switching-on the power supply, heaters and the blowers. The heater switch may be set at maximum heat position so as to attain heater temperature at about 740C. The temperature recorder should be set to record temperature at every five min or make continuous pen-line recordings as the case may be, colour coded for each sensor, on a graph paper readable in tenths of a degree in Celsius. After warm-up period, the frequency of temperature recordings should be increased to once every two minutes. The dwell time would start when core temperature of wood blocks attains the temperature of 560 C. The delivery air must be warmer than the targeted core temperature, but this matter would be left to the discretion of operator. The operator could have the flexibility to change the temperature of delivery of air at various times during treatment as well as blower speed.


Post-Treatment Procedures


       At the end of process, the chamber should be allowed to cool down gradually to an ambient temperature before the door is opened. It should be ensured under no circumstances the treated wood got mixed up with raw wood or stored along side with raw wood package material to prevent cross-infestation.


Marking of treated solid-wood packaging material


The treated wood packaging material should be marked as per the mark assigned to the approved facility. The mark should be affixed at visible location and should be stenciled with the black ink or paint (not washable) as suggested in the enclosure to the certificate of approval.


  1. Heat Treatment Facilities for Niger Seed for Export to USA


Niger (Guizotia abyssinica) seed from any foreign country shall be permitted import into USA subject to the phytosanitary requirements that the Niger seed at or before the time of arrival at the first port of entry shall be heat treated for possible infestation with noxious weeds or prohibited pathogens in accordance with the applicable provisions of USDA PPQ Treatment Manual. The initial certification of facility will be co-conducted by the Centre for Plant Health Science and Technology (CPHST), USA and the Directorate of Plant Protection, Quarantine & Storage (Dte of PPQS). Subsequently the Dte of PPQS will be entrusted with responsibility for re-certification.


The Niger seed treatment facility is required to run with maximum capacity at the longest treating period viz. at least 15 minutes at minimum of 248 0 F or 120 0C.


Subsequently, all precautions must be taken for not mixing the treated bags with the untreated ones. To facilitate the treatment providers, detail guidelines have framed by the Government of India in the form of National Standard “Heat Treatment Facilities for Niger Seed for Export to USA”.


  1. Vapour Heat Treatment Facilities for Fresh Fruits & Vegetables (VHT)


       Sometimes, the importing country stipulates the requirement of Vapour Heat Treatment for fresh tropical fruits & vegetables against fruit flies. This treatment uses heated air which is saturated with water vapour to raise the temperature of the commodity to a required point and holds the temperature for a specified period. The latent heat released by the condensation of the vapour on the commodity raises the pulp temperature quickly and evenly and thus prevents damage to the commodity. In application, a fine mist and air under forced circulation is present with the saturated vapour. A National Standard “Vapour Heat Treatment Facilities for Fresh Fruits & Vegetables” describes the authority to approve the facilities, application procedures for certification, minimum requirements of the facility, preliminary performance testing, official performance testing and certification of facility.


The temperature-time relationship varies with the commodity and the pest involved. In case of treatment against fruit flies, the pulp temperature of the commodity will be raised by the saturated water vapour to 46-48 0C during a ramp up time of 4 hours and then the fruits will be held at the required temperature for a period of 30 min. The exposure periods and the treatment temperatures will vary with kind of fruit fly species and commodity involved. Where more than one fruit fly species is known to infest a commodity, laboratory experiments should be carried out with 100-1000 individuals for determining the most heat tolerant species. The small-scale trials should be carried out with 3000-5000 individuals to determine the most-heat tolerant stage of determined fruit fly species and this should be further confirmed by large scale treatment trials involving 30,000 populations of first instar larvae of the most heat tolerant fruit fly species, ensuing Probit 9 security level to prove the efficacy of treatment for commercial application.


Treatment Procedure


Temperature sensors are used to determine the pulp temperature of the commodity under treatment, psychrometers are used to determine the existing relative humidity. The tips of the sensors are inserted in the centers of individual fruits and vegetables. Vapour heat processors employing a duct system, which delivers the vapour directly to each individual stack of commodity and which channels the air flow directly through the stack, may utilize the following sensor placement: Bottom, Middle, and Top Layers (A total of 9 sensors); Hot air duct—2 sensors (1 wet, 1 dry = psychrometer);


Vapour heat chamber equipment should be tested for correct functioning before each treatment. The accuracy of each temperature sensing element should be checked once a month during regular use with water at temperatures near the normal treatment temperatures. All sensors, after calibration corrections, must register the required temperature or above at the beginning of treatment. A 0.3 °C deviation is considered within the range of acceptable tolerance thereafter. This tolerance applies to the humidity check sensors as well as those for host temperature recordings. Extend the treatment time by an amount equal to any periods when specifications are not met. Chambers must be equipped with recording temperature and humidity indicators. Detailed records of each treatment must be kept. Final calibration values for each temperature sensor must be recorded for the port files.


Post-treatment Cooling


The fruits and vegetables should be cooled immediately after VHT treatment. Allowing the fruit to simply stand for at least 30 minutes after removal from the VHT chamber in insect proofed and well-ventilated room would be helpful before the fruits and vegetables subject to pre-cooling process. The recommended storage temperature for mangoes is 55 °F to 57 °F (12.8 °C) at 85 to 90% relative humidity.


Japan accepts certain varieties of Mangoes from India with special requirement of Vapour Heat Treatment. In this facility, the fruits shall be disinfested in saturated water vapor. The air temperature inside the treatment chamber shall be raised step by step to 50°C or above, so that the pulp temperatures of the center of the fruits shall be raised to 47.5°C and be kept continuously at 47.5°C or above for 20 minutes.


Hot Water Immersion Treatment Facilities for Mango Fruits


A National Standard “Hot Water Immersion Treatment Facilities for Mango Fruits” has been formulated which describes the procedures for certification of hot water immersion treatment facilities for treating fresh fruits of mango against fruit flies in compliance with phytosanitary requirements. Hot water treatment facilities are primarily used for treating tropical fruits against treptidae fruit flies. In this treatment the fruits are exposed to a temperature of at least 46.1-47.8 0C (1150 and 1180F) by immersing in heated water for a specified period of time depending upon the specific pest, type of fruit (species/variety) and size of fruits. It is further essential to maintain constant and uniform temperature during the period of treatment to ensure effective treatment. The time-temperature relationship varies with the commodity and pest. Usually, the pulp temperature of the fruit is raised using heated water between 46.1-47.8 0C (1150 and 1180F) for prescribed period of time.