@granul3]. The plateaus are formed stochastically and can therefore not be observed after averaging over various samples (figs. \[plot\_5\], \[plot\_5b\]).

Note that also the variance of the evacuation time increases strongly with $\mu$. Fig. \[plot\_7\] shows that the average evacuation time $T$ is not always a meaningful quantity for safety estimates since the variance can become quite large. For the very small density $\rho=0.003$ the gradient of the curve is rather flat at the beginning of the evacuation (fig. \[plot\_7b\]). Here there are only few particles in the system and no cue is formed near the exit.

Mean-field approximation for the ordered regime
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As we have seen in Sec. \[timevolv\] the curve of the number of evacuated persons $N(t)$ grows almost linearly in the ordered regime, especially for high densities $\rho$. For this regime we now calculate approximatively the $\mu$-dependence of this curve, i.e. $N=N(t,\mu)$.

As explained earlier, in the ordered regime after a short time a big jam forms at the door due to the strong coupling to the static field $S$. Fig. \[plot\_8\] shows a typical local configuration in front of the exit.

![Typical configuration in front of the door in the ordered regime.[]{data-label="plot_8"}](\DIR/fig15.eps){width="0.4\columnwidth"}

Generically, 3-particle conflicts 