\newcounter{testi}
\newcounter{testii}
\newenvironment{fisken}[1]{%
    \begin{longtable}[H]{|p{1.5cm}|p{5.5cm}|p{5.0cm}|}
    \hline
    & Demand
    & Comment
    \tabularnewline\hline
    \endfirsthead
    \hline
    & Demand
    & Comment
    \tabularnewline\hline
    \endhead
    \endfoot
    \endlastfoot

    \newcommand{\tast}[1]{%
        \stepcounter{testi}\setcounter{testii}{1}
        \thetesti.\thetestii & #1 & c \tabularnewline\hline
    }{}
    \newcommand{\trist}[1]{%
        \stepcounter{testii}
        \thetesti.\thetestii & #1 & c \tabularnewline\hline
    }{}

}{
    \caption{Security requirements specification}
    \label{tbl:sec_req}
    \end{longtable}
}

\begin{fisken}{}
    \tast{asdf}
\end{fisken}