- Nitrosamines and Possible Curing Barn Modifications

Near the end of 1999 it became common knowledge that tobacco workers had determined the mechanism of nitrosamine formation in flue-cured tobacco and suggested changes to the curing systems commonly used in the United States. At the time of this publication their differing opinions within the industry on how best to deal with this problem and how to pay for possible barn curing system conversions.

This is a summary of a report from several R.J. Reynolds Tobacco Company employees after they have done research on nitrosamines: Nitrosation of naturally occurring tobacco alkaloids is commonly accepted as the mechanism of tobacco specific nitrosamine (TSNA) formation in tobacco. As minimal-to-no TSNA are present in green tobacco, TSNA formation and accumulation are generally considered to occur during curing.

Most recent hypotheses focus on microbial reduction of nitrate to nitrite and other oxides of nitrogen that react with tobacco alkaloids to form TSNA during curing. This natural microbial process remains the prevalent hypotheses for TSNA Formation in cured burley tobacco. However, a second mechanism for the formation of TSNA, independent of microbial activity, is presented in this work on flue-cured tobacco.

It is common practice to flue-cure Virginia or blonde tobacco in bulk barns that incorporate forced air ventilation and temperature control. Modem bulk barns generally use liquid propane gas (LPG) with direct-fired burners that exhaust combustion gases directly into the barn where the tobacco is exposed to those combustion gases. Our studies indicate that LPG combustion by-products react with naturally occurring tobacco alkaloids to form TSNA. Heat exchange curing methods preclude exposure of the tobacco to combustion gases and by-products, thereby eliminating this significant source of TSNA formation, without degrading leaf quality or smoking character.

For decades, nitrosamines have been a focus of considerable research for which references abound in the scientific literature. The presence of nitrosamines in cigarette smoke and their possible role in tobacco carcinogenesis were first postulated in the scientific literature in 1962. Decades of research have provided no basis for concluding cause and effect relevancy of nitrosamines to chronic disease in smokers, despite implied contentions to the contrary. Without such relevancy, the effect of reducing levels of nitrosamines in tobacco or tobacco smoke cannot be definitively asserted. However, responsible product stewardship advocates that technologies to reduce nitrosamine levels in tobacco be pursued and implemented as proven effective and commercially practicable.

Extensive research by many investigators since the 1970's reported the presence of as many as thirty-five nitrosamines in cigarette smoke. A subset of those nitrosamines was considered to be specific to tobacco, resulting from nitrosation of endogenous tobacco alkaloids. Today, eight tobacco specific nitrosamines have been identified and seven have been reported as present in cigarette smoke. The breadth of TSNA investigations over the last three decades spans a wide range of topics including formation and accumulation of TSNA in tobacco, quantitative analyses of TSNA in tobacco and tobacco smoke, epidemiology, animal studies, and possible chronic health effects of TSNA in smokers.

It is common practice to flue-cure Virginia or blonde tobacco in bulk barns that incorporate forced air ventilation and temperature control. The flue-curing process typically takes from five to seven days and involves three sequential steps of yellowing, leaf drying and stem drying. Generally, the yellowing phase requires 36 to 72 hours in which dry bulb temperature and relative humidity are maintained at approximately 35'C and 85%, respectively. During the next 48-hour leaf-drying phase, temperature is slowly ramped from 35' to 60' and relative humidity dropped to 35%. The last 48- hour stem-drying phase is carried out at 75'C and relative humidity allowed to drop to approximately 18%. Finally, the tobacco is allowed to reorder for post-cure processing. The quality of flue- cured tobacco Is highly dependent an temperature and humidity control within the barn such that natural biochemical changes are allowed to occur while the process of drying the leaf and stem take place.

In the U.S. today, flue-cured tobacco is predominantly cured in commercial bulk barns. As a result of energy pressures in the U.S. during the 1960's, farmer-built "stick barns" with heat- exchanged flue systems were gradually replaced with more energy efficient bulk barns using direct-fired liquid propane gas (LPG) burners. These LPG direct-fired burner systems exhaust combustion gases and combustion by-products directly into the barn where contact is made with the curing tobacco.

In stark contrast to direct-fired curing, heat-exchange burner configurations completely vent combustion gases and combustion by-products to the external atmosphere rather than into the barn The heat-exchange process precludes exposure of the tobacco to LPG combustion by-products, thereby eliminating an important source of nitrosating agent for TSNA formation.

The Tobacco Industry Leadership Group met before Christmas to discusss the Nitrosamine Issue. A sub-committee was appointed to discuss the specifics of incorporating the heat exchanger technology into the curing barns currently used in the US. After a sub-committee report on January 7, 2000, a sub-sub-committee was appointed to consider and compose standards for heat exchangers to be considered.

Following is a summary of the January 21, 2000 meeting and the DRAFT version of the standards submitted. Dr. Boyette did an excellent job of reporting the activities of the meeting and presenting the standards at he meeting. For this reason I have included below his version of the meeting.

------- Forwarded Message Follows -------
From: "Michael D Boyette"
Subject: Tobacco Leadership Subcommittee Meeting Agents and Specialists:

The following is sent for your information concerning ongoing efforts
to implement a method and means to reduces TSNA's in US Flue-Cured Tobacco.
****************************************

The Barn Conversion Subcommittee of the Flue-Cured Tobacco Leadership Committee (an ad hoc committee composed of all segments of the flue-cured industry) met on January 21, 2000 at 10:00 a.m. at the offices of the North Carolina Farm Bureau in Raleigh. The meeting was chaired by Billy Carter, president of the North Carolina Tobacco Growers Association.

Dr. Mike Boyette of NCSU, chair of the committee to draft standards for low TSNA curing barns, presented a draft proposal to the committee. (Attached) The committee closely reviewed the proposal and suggested only minor changes. It was agreed that the draft standards would be sent to all interested parties for comment. It is anticipated that the subcommittee will adopt the standard at its next meeting on February 1, 2000. Once adopted by the Subcommittee, the standard will be presented to the full committee at a date yet to determined.

The Curing barn and equipment manufacturers were asked to discuss possible costs of barn conversions. Prices ranged from $5000 to $6000 not including installation. All manufacturers present stated that they were actively involved in research and development and had received numerous grower inquiries but as of yet, were not actively manufacturing units for sale.

The subcommittee discussed the need to adopt a time line to complete conversion of all needed barns but this was delayed until the next meeting. The group agreed that substantial reduction or elimination of TSNA's in US flue-cured tobacco was of utmost importance and should be completed as s as possible. July 1, 2001 was considered a likely workable date to establish a certification process.

The subcommittee discussed financing of the barn conversion project. It was agreed the the subcommittee would receive proposals from all interested parties until noon on January 28, 2000.

These proposals should be directed to: Mr. Fred Fox NC Farm Bureau 5301 Glenwood Avenue P.O. Box 27766 Raleigh, NC 27611 USA Telephone: 919-782-1705 FAX: 919-783-3593 E-mail: ncfbfed@ncfb.com

Draft Recommendations for Indirect-Fired Heating Systems
for Tobacco Bulk Curing Barns

Introduction

In response to ongoing research concerning the production of tobacco specific nitrosomines (TSNA) in flue-cured tobacco during the curing and handling process and its associated health concerns, the Flue-Cured Tobacco Leadership Committee has developed these recommendations for heating and air handling equipment that may be installed as retrofitted equipment in existing curing barns and as original equipment in new barns and such equipment is specifically warranted to significantly reduce or eliminate TSNA causing factors as described below.

The present research suggests that TSNA's are developed, in part, during the curing process by a chemical reaction between nicotine contained in the uncured leaf and various oxides of nitrogen (NOx) found in all combustion gasses, regardless of fuels. The significant reduction or elimination of these nitrogen compounds in the curing air has been shown to substantially reduce or eliminate to undetectable levels, TSNA's in cured tobacco.

The curing of bright-leaf tobacco by the controlled application of supplemental heat was first developed over 160 years ago. Prior to 40 years ago, tobacco was cured in grower built structures that were heated either with direct-fired (products of combustion freely in contact with the curing leaf) or with some type of indirect-fired (utilizing a heat exchanger or flue) that conducted the products of combustion away from the curing leaf. Previous to the current discussion, barns utilizing either direct-fired or indirect-fired systems were considered to be capable of producing cured leaf of excellent and commercially indistinguishable quality.

The first commercial tobacco bulk curing barn was sold in 1960. Since that time, is estimated that more than 60,000 barns have been sold in the flue-cured tobacco producing region of the southeastern US. It is also estimated that no more than 50,000 of these units are still in operating condition. From 1960 to the mid-1970's, a large portion of all barns manufactured employed oil-fueled, indirect fired heating systems. Many of these barns are still in use. After the mid-1970's, most new barns employed natural or LP gas, direct-fired systems. The reason for this change was the significant equipment cost and maintenance costs differentials between gas and oil fueled equipment. Further, the assumed future availability of gaseous versus liquid fuels and especially the relatively greater efficiency (20 to 40 percent) of direct-fired versus indirect-fired heating systems prompted most growers to purchase LP gas barns.

Recommendations

1. General

1.1 These recommendations may be applied to all indirect-fired heating systems and components designed for curing flue-cured tobacco regardless of construction, fuel type or Btu output.

1.2 These recommendations may be applied to existing as well as newly constructed barns.

1.3 These recommendations may be applied to complete curing systems retrofitted into existing or new manufactured barns as well as heating and/or air handling equipment and components retrofitted into existing barns.

1.4 Portions of these recommendations may apply to tobacco curing systems employing external combustion such as hot water or steam systems as well as electric resistance or other types of systems where fuel combustion does not occur within the confines of the barn.

1.5 These recommendations do not apply to direct-fired curing systems of any design or fuel type.

1.6 A curing system that otherwise complies with these recommendations shall not be acceptable if it has features that impair the results intended by these requirements (i.e., the reduction or elimination of TSNA's from cured leaf).

1.7 To comply with these recommendations, equipment shall first comply with all applicable sections of ASAE Standard: ASAE S248.3, latest revision, "Construction and Rating of Equipment for Drying Farm Crops."

1.8 All curing systems, equipment or components complying with these recommendations shall also comply with any other applicable recommendations, laws, rules, guidelines or codes. A partial list of potentially applicable standards are shown below. Standards other than those shown may also apply.

2. Construction

2.1 Each curing system or component shall be constructed of entirely new unused parts and materials.

2.2 Equipment shall be constructed of materials suitable for the intended purpose and of sufficient strength and durability to ensure safe and reliable service of the parts and assembly for an extended period of service.

2.3 All equipment shall have all shields, screens and other safety devices for the protection of life and property.

2.4 Provisions shall be made to permit ready observation of and reasonable access to all parts for assembly, maintenance and repair.

2.5 Curing systems shall be designed in such manner as to prevent the products of combustion from entering the curing air in any quantity and in any manner for the warranted life of the system. Means by which combustion gasses may enter the curing air include, but are not limited to: heat exchanger cracks, weld voids, drafts, improper flue seals, corrosion openings, flame erosion openings and improper mountings.

2.6 Curing systems warranted to comply with these recommendations shall be subject to tests and examinations by North Carolina State University or an independent testing agency under the direct supervision of NCSU, for the levels of nitrous oxides and other combustion gasses in the curing air and level of TSNA's in the cured leaf. Additional tests of performance, efficiency, reliability and general fitness for the intended application may be conducted by application from either manufacturer or owner of the subject equipment.

2.7 The full results of any test, in writing, will be provided by the testing agency to the manufacturing and/or owner of any tested equipment. Additionally, these test results may be published or otherwise made available to the public through the proper channels of North Carolina State University or the North Carolina Cooperative Extension Service.

3 Applicability

3.1 It shall be sole responsibility of the vendor of curing equipment, either new air handling and heating systems in new barns, new air handling and heating systems as retrofits to existing barns or new components as retrofitted equipment to existing barns, to ensure that such equipment is entirely compatible with the other components of the barn.

3.2 Where systems or components are retrofitted into an existing barn, it shall be the sole responsibility of the vendor to ensure such equipment meets or exceeds the specifications of the original equipment and that the heating and air handling system, in general, likewise meets or exceeds the specifications of the original equipment in the original barn in terms of heat output, air handling capacity (in terms static pressure and flow rate), electrical requirements and general suitability for its intended functions. (i.e., A vendor of a retrofitted heat exchanger shall acknowledge and correct for the added air resistance of that heat exchanger if the added resistance reduces the static pressure and flow rate of the existing air handling system to an unacceptable level for the proper curing of tobacco.)

3.3 Equipment complying with these recommendations shall have little or no effect on the curing schedule in terms of time to complete the cure or the proper control of temperature and humidity as is customarily practiced by the grower with that particular model of barn and tobacco in terms of stalk position, loading capacity or other variable as they arise.

3.4 It shall be the responsibility of the vendor of all barns and equipment complying with these recommendations, either new-built or retrofitted, to ensure that nothing in the design, installation, maintenance or operation of this equipment negatively impacts the purchaser acceptability of the cured leaf removed from these barns. (i.e., The quality of tobacco from barns complying with these recommendations shall meet or exceed the purchaser acceptability customarily expected from a similar barn prior to conversion.)

Definitions:

1. Retrofit. The process and equipment whereby a tobacco curing barn is brought into compliance with these rocommendations.

2. Direct combustion curing system. A system where the combustion gasses are introduced directly into the curing air stream and hence into contact with the curing leaf.

3. Indirect combustion curing system. A system where the combustion gasses are prevented from entering the curing air stream by flues or pipes and the heat is extracted by conduction and forced-convection from a suitable heat exchange apparatus.

4. Curing system. The combination of heating and air handling system for curing tobacco including all auxiliary components and controls. Reference List of Applicable Recommendations The following is a partial list of reference specifications and recommendations pertaining to the design, manufacture, installation, maintenance, testing or use of equipment or potential components for curing tobacco or similar applications.

AMCA 210-67 Standard Tests for Air Moving Devices

ANSIZ83.1 Installation of Gas Piping and Gas Equipment on Industrial Premises and Certain other Premises

ANSI Z91.1-1972 Performance Standards for Oil-Powered central Furnaces

ASME CSD 1-1995 Control and Safety Devices for Automatically Fired Boilers

ASAE S248.3 Construction and Rating of Equipment for Drying Farm Crops

CAN/CGA-3.8-M86 Gas-Fired Equipment for Drying farm Crops

ISO 65.160 Standards for Tobacco, Tobacco Products and Related Equipment.

NFPA No. 31 Standards for Installation for Oil Burning Equipment

NFPA No. 54 Standards for Installation for Gas Appliances and Gas Piping

UL 296 Standards for Oil Burners

UL 731 Oil-Fired Heaters

UL 795 Commercial Industrial Gas Heating Equipment

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