-- *** Test Data ***
DECLARE @t TABLE
(
    ToolId int NOT NULl
    ,time_occurred datetime NOT NULL
    ,alarmtext varchar(50) NOT NULL
)
INSERT INTO @t
SELECT 1,  '20090514 12:20', 'DOOR OPEN' UNION ALL
SELECT 1,  '20090514 12:22', 'DOOR OPEN' UNION ALL
SELECT 1,  '20090514 12:30', 'DOOR OPEN' UNION ALL
SELECT 2,  '20090514 12:20', 'DOOR OPEN' UNION ALL
SELECT 2,  '20090514 12:24', 'DOOR OPEN'
-- *** Test Data ***

;WITH cte (ToolId, time_occurred, alarmtext)
AS
(
    SELECT ToolId, time_occurred, alarmtext
    FROM
    (
        SELECT ToolId, time_occurred, alarmtext
            ,ROW_NUMBER() OVER (PARTITION BY ToolId, alarmtext ORDER BY time_occurred) AS RowNum
        FROM @t
    ) D1
    WHERE RowNum = 1

    UNION ALL
    
    SELECT ToolId, time_occurred, alarmtext
    FROM
    (
        SELECT T.ToolId, T.time_occurred, T.alarmtext
            ,ROW_NUMBER() OVER (PARTITION BY T.ToolId, T.alarmtext ORDER BY T.time_occurred) AS RowNum
        FROM @t T
            JOIN cte C
                ON T.ToolId = C.ToolId
                    AND T.alarmtext = C.alarmtext
                    AND T.time_occurred >= DATEADD(minute, 5, C.time_occurred)
    ) D2
    WHERE RowNum = 1
)
SELECT *
FROM cte
ORDER BY ToolId, time_occurred, alarmtext