"Managing Tobacco Greenhouses
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Tobacco greenhouses are susceptible to storm damage, particularly high winds and heavy snows. To reduce any potential damage, growers can take several steps to lessen the likelihood and severity of damage.
1. Provide an alternative electrical power source. - Most covers torn or destroyed due to high winds are damaged as a result of a loss of electrical power to the inflation fans. Uninflated covers have 6 to 10 times more wind resistance than fully inflated covers. Even new covers cannot continually withstand rapid flexing in cold temperatures. A small electrical generator (5 to 10 kilowatts) can easily provide enough power to operate the inflation fans and the gas heaters. For safety, an auxiliary generator must be connected through an approved transfer switch.
2. Maintain inflation of the top. - Lastly, it is better to maintain inflation of the cover with a generator than to allow it to deflate and flap. If inflation cannot be maintained, again, cutting the cover so that it blows off the house may be the best option.
3. Provide additional structural bracing. - Installing horizontal cables or tubes provides additional strength to resist snow loads. Knee-braces and gussets can also substantially decrease the likelihood of damage from both wind and snow loads. Horizontal cables or tube braces provide only a modest improvement in resistance to wind loads.
4. Raise the curtains before the storm. - As a general rule, greenhouses should be closed with curtains being raised. If the curtains are left down, sudden gusts of wind can put pressure on the underside of the structure and unevenly load it to be damaged. The style of greenhouse that is used in tobacco production is designed to resist vertical pressure ONLY. Pressure from the side or from one side only usually causes the most damage.
5. Remove the top to prevent structure damage. - If the wind rips the plastic and it starts whipping violently, wind pressure may be exerted in the place where the plastic is still attached. This is also likely to cause failure. Once the plastic rips, it is best to remove it completely. NOTE: AVOID RISK OF PERSONAL INJURY! Plastic which is partially torn but lying limp may actually PULL the GREENHOUSE DOWN!
6. Do not allow water or snow to accumulate on sagging covers. - The weight of water or snow which can accumulate on the top of the greenhouse can cause them to collapse. Once water starts to collect in the plastic, it is better to punch a hole in it than to allow it to destroy the entire structure. If the power is lost and inflation cannot be maintained, covers should be cut or removed from the structure.
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.