Esterel is a synchronous programming language historically defined for system control, well suited to react in parallel to external sensors, intensively used in avionics. Recently, with the incoming of the orchestration language HipHop, a domain-specific language of the multi-tier language Hop, Esterel is used to manage Web requests. In this context, where orchestration programs are dynamically generated, long compilation preamble to computation must be avoided and a simple and fast interpreter is preferred. This paper presents such an interpreter. Esterel's processes communicates through signals and one particularity of this language is its ability to instantaneously react to the absence of a signal. In this paper we present a static analysis which allows the interpreter to predict the absence of a signal.