localWMS = new OpenLayers.Layer.WMS( "Local WMS layers",
                  "http://127.0.0.1:8080/cgi-bin/mapserv.exe?MAP=C:/MapServer/raster.map",
                  {layers: 'polygon',transparent: true,alpha:true},
                  { projection:new OpenLayers.Projection("EPSG:4326"),
                    units:'m',
                  isBaseLayer: false}
                  );

 map.addLayer(localWMS);

LAYER
DATA "PG:host=*** dbname=*** schema=public table=london where='rid=3' mode='1'"
NAME "postgis"
PROCESSING "SCALE=AUTO"
PROCESSING "NODATA=-9999"
STATUS DEFAULT
TYPE RASTER

UNITS METERS
CLASS
  NAME "Minor Impact"
  EXPRESSION ([pixel] >= 0 AND [pixel] < 1.29525335532 )
  STYLE
    ANGLE 360
    OPACITY 50
    COLOR 122 182 245
    SYMBOL 0
    WIDTH 1
  END
END
CLASS
  NAME "Moderate Impact"
  EXPRESSION ([pixel] >= 1.29525335532 AND [pixel] < 2.59050671063 )
  STYLE
    ANGLE 360
    OPACITY 50
    COLOR 76 230 0
    SYMBOL 0
    WIDTH 1
  END
END
CLASS
  NAME "Severe Impact"
  EXPRESSION ([pixel] >= 2.59050671063 AND [pixel] < 5.69911476339 )
  STYLE
    ANGLE 360
    OPACITY 50
    COLOR 252 228 91
    SYMBOL 0
    WIDTH 1
  END
END
CLASS
  NAME "Catastrophic"
  EXPRESSION ([pixel] >=5.69911476339 )
  STYLE
    OPACITY 30
    COLOR 232 16 20
  END
END
END

LAYER
DATA "PG:host=*******************'"
NAME "postgis"
PROCESSING "SCALE=AUTO"
PROCESSING "NODATA=-9999"
STATUS DEFAULT
TYPE RASTER
OPACITY 50
UNITS METERS

LAYER
NAME 'Raster'
TYPE RASTER
CONNECTIONTYPE postgis
CONNECTION "user=postgres password=... dbname=... host=..."
DATA "bytea FROM rasters"
STATUS OFF
OFFSITE 0 0 0
TRANSPARENCY 100
END

LAYER
DATA "PG:host=*** dbname=*** schema=public table=london where='rid=3' mode='1'"
NAME "postgis"
PROCESSING "SCALE=AUTO"
PROCESSING "NODATA=-9999"
STATUS DEFAULT
TYPE RASTER
OPACITY 50

UNITS METERS
CLASS
  NAME "Minor Impact"
  EXPRESSION ([pixel] >= 0 AND [pixel] < 1.29525335532 )
  STYLE
    ANGLE 360
    COLOR 122 182 245
    SYMBOL 0
    WIDTH 1
  END
END
...

var mapParams = {
                  'layers': 'postgis',
                  'transparent': true
                   }
 var layer_wms = new OpenLayers.Layer.WMS(
                mapParams['layers'],
                serverURL,
                mapParams
            );
 map.addLayers([layer_wms]);