PHP times out and Firefox crashes due to adding var_dump to code

Question

I try to rewrite this Python code in PHP. Currently I'm debugging it and strange thing happens: when I add var_dump in the piece of code, where Apache2 error log reports:

HP Fatal error: Call to a member function setext() on a non-object

then Firefox crushes and error.log claims:

[core:notice] [pid 2090] AH00052: child pid 14768 exit signal Segmentation fault (11)

and

Maximum execution time of 30 seconds exceeded

Caused by following function (var_dump is commented out):

function load($filename){
    /***************************************************************
    Load in a database and interpret it as a network

    First column must be unique keys which define the instance units.
    Each column is a pool (names, gangs, ages, etc).
    Every row is mutually excitory.
    ****************************************************************/
    global $units, $pools, $unitByName;
    $units = array();
    $pools = array();
    $handle = fopen($filename, "r");
    while (($line = fgets($handle)) !== false) {
        $relatedUnits = preg_split('/\s+/', $line);
        if (empty($relatedUnits)) continue;
        $key = count($units);
        foreach ($relatedUnits as $k => $ru){
            if ($k >= count($pools)){
                $pools[] = new Pool;
            }
            $pool = $pools[$k];
            if (in_array($ru, $unitByName)){
                $unit = $unitByName[$ru];
            } else {
                $unit = new Unit($ru, $pool);
                $units[] = $unit;
            }
            $pool->addMember($unit);
            if ($k > 0){
                $units[$key]->addExciter($unit);
                $unit->addExciter($units[$key]);
            }
        }
    }
    fclose($handle);
    //var_dump($pools);
}

Without var_dump code executes properly. Here whole code is pasted (it's still buggy, I'm aware of this ;)