function populateSecondGas(CTRL, firstGas) {
		
		switch (firstGas) {

			case "CO":
				GasName = new Array( "H2S", "CL2", "HCN", "NH3", "NO", "NO2", "SO2", "Hydride" )
				break
			case "H2S":
				GasName = new Array( "CO", "HCN", "NO", "SO2", "Hydride" )
				break				
			case "CL2":
				GasName = new Array( "CO", "NO", "Hydride"  )
				break
			case "HCN":
				GasName = new Array( "CO", "H2S", "NH3", "NO", "Hydride" )
				break				
			case "NH3":
				GasName = new Array( "CO", "HCN", "NO2", "Hydride" )
				break				
			case "NO":
				GasName = new Array( "CO", "H2S", "CL2", "HCN", "NO2", "Hydride"  )
				break
			case "NO2":
				GasName = new Array( "CO", "NH3", "NO", "SO2", "Hydride"  )
				break
			case "SO2":
				GasName = new Array( "CO", "H2S", "NO2", "Hydride"  )
				break
			case "Hydride":
				GasName = new Array( "H2S", "CL2", "HCN", "NH3", "NO", "NO2", "SO2" )
				break		
			case "ALL":
				GasName = new Array("CO", "H2S", "CL2", "HCN", "NH3", "NO", "NO2", "SO2", "Hydride" )
				break																																																
			default:
				GasName = new Array();
		}		
		i=0
		while (i<CTRL.length) {
			CTRL.options[i] = null 
		}
		i=0
		while (i<GasName.length) {
			newOpt = new Option(GasName[i], GasName[i], false, true) 
			len = CTRL.length 
			CTRL.options[len++] = newOpt 
			i++
		}		
	}
	populateSecondGas(frm_manager.FirstGas, "ALL")
	populateSecondGas(document.frm_manager.SecondGas,document.frm_manager.FirstGas.options[document.frm_manager.FirstGas.selectedIndex ].value)