-12- 



can damage the catalyst as mentioned earlier. 



With each pass of the storage room atmosphere through the 

 catalyst of the recirculatory system, a reduction of 3 to 41 oxygen 

 is obtained. When the oxygen level of the CA storage room reaches 

 51, the fuel flow must be reduced to about one-half the initial 

 rate as recommended by the manufacturer. With insufficient oxygen, 

 propane is 'cracked' to carbon monoxide and ethylene. Moreover, 

 as oxygen becomes limiting this reduces the amount of propane 

 oxidized so the temperature of the catalyst will decrease. When 

 the catalyst temperature decreases to the low temperature thermo- 

 stat setting this turns the fuel supply and the equipment off. 



If there is any question of propane or other combustible gases 

 in the storage room when using a recirculatory system, simply 

 turn off the fuel supply but continue to recirculate the CA room 

 atmosphere through the generator. This will remove the combustible 

 gases from the storage room and the catalyst will remain hot until 

 the gases have been reduced to safe levels. Several users of 

 Arcat and COB units routinely do this to scrub out the combustible 

 gases after an oxygen pull-down. 



A survey of CA storage room atmospheres was conducted in 

 Michigan after the Peabody storage explosion. It revealed that the 

 amount of combustible gases such as carbon monoxide, ethylene, and 

 propane in storage rooms varied widely even between rooms at a 

 single storage location depending on the type of CA generator used 

 and how it operated. Since the explosion, no instances have been 

 found where propane or other combustible gases approached explosive 

 levels. Propane levels of 0.1 to 0.51 are commonly found where Arcat 

 units have been employed. In one storage 1.71 propane was found and 

 this was lowered by recirculating the atmosphere through the CA 

 generator. Similar experiences of significant levels of combustible 

 gases in CA storage rooms have been observed in New York and Washing- 

 ton with Arcat, COB, Wilde and Tectrol units. These experiences 

 point out the need to more carefully monitor the operation of CA 

 generators to see that they are operating properly to ensure com- 

 plete oxidation of the fuel being used. Safety devices such as 

 thermostats for high and low temperature cut-off should be tested. 

 Air pressure switches, fuel regulators and solenoid valves should be 

 checked. 



An additional safety device such as a combustible gas sensor 

 could be installed in the exhaust of the CA generator to shut-off 

 the equipment and fuel supply to prevent a significant amount of 

 fuel or products of incomplete combustion from entering the storage 

 room. The Acotec oxygen/ethylene scrubber now under test at Chase 

 Fruit Storage in Sparta, Michigan has a combustible gas sensor as 

 a component of the safety controls. The Acotec unit is designed to 



