False positive (FP) decreasing methods

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Hello Everyone! I made object detection for fire extinguisher usinng LBP cascade training. Have 5000 positives (1000 initial) and 5000 negatives. Everything works fine but i have one problem. I get a little bit too much FP. Yes i took about 500 pictures of environment and also downloaded from internet pictures that are best for my example (walls, tiles,etc..) and put it all in negatives folder. But it still doesn't do it. I am thinking about implementing some kind of algorithm in my code that will help me to decrease FP. My idea is some kind of "time filter" that will eliminate positives that last less than x frames (for example 4 frames --> x=4). Is it good idea and is it doable?

Here is my .cpp detector code:

#include <highgui.h>
#include <iostream>
#include <stdio.h>
#include <cv.h>
#include<string>

using namespace std;
using namespace cv;
using namespace std;

int main() {
    cvNamedWindow("fire_extinguisher detecting camera", 1);
    // Capture images from any camera connected to the system
    CvCapture* capture = cvCaptureFromAVI("/home/painkiller/Desktop/video/13.mp4");

    // Load the trained model
    CascadeClassifier fire_extinguisherDetector;
    fire_extinguisherDetector.load("src/fire_extinguisher.xml");

    if (fire_extinguisherDetector.empty()) {
        printf("Empty model.");
        return 0;
    }

    char key;
    while (true) {
        // Get a frame from the camera
        Mat frame = cvQueryFrame( capture );

        stringstream x,y;
        std::vector<Rect> fire_extinguishers;

        // Detect fire_extinguisher
        fire_extinguisherDetector.detectMultiScale(frame, fire_extinguishers, 1.1, 30,
                0 | CV_HAAR_SCALE_IMAGE, Size(250, 700));

        for (int i = 0; i < (int) fire_extinguishers.size(); i++) {
            Point pt1(fire_extinguishers[i].x, fire_extinguishers[i].y);
            Point pt2(fire_extinguishers[i].x + fire_extinguishers[i].width,
                    fire_extinguishers[i].y + fire_extinguishers[i].width);

            x << fire_extinguishers[i].x;
            string strx = x.str();

            y << fire_extinguishers[i].x;
            string stry = y.str();

            // Draw a rectangle around the detected fire_extinguisher
            rectangle(frame, pt1, pt2, Scalar(0, 0, 255), 2);
            putText(frame, strx + " is x and " + stry + " is y", pt1, FONT_HERSHEY_PLAIN, 1.0,
                    Scalar(255, 0, 0), 2.0);

        }

        // Show the transformed frame
        if (!frame.empty())
        imshow("fire_extinguisher detecting camera", frame);

        // Read keystrokes, exit after ESC pressed
        key = cvWaitKey(10);
        if (char(key) == 27) {
            break;
        }
    }

    return 0;
}