Most oil refineries and factories producing basic chemical products are located in port areas, with the result that industrial complexes potentially have a strong environmental impact on their area of influence. These externalities result in a loss of welfare for citizens residing in neighbouring areas. In a context of sustainable development, companies must integrate concerns about the natural environment in their business strategy. External stakeholders, as residents, find it difficult to visualize the actions firms take to reduce their environmental impact, and the adoption of voluntary certified environmental management systems (EMSs) acts as a signal indicating the adequate environmental behaviour of these companies. These certifications enable companies to achieve the social legitimacy they need for long‐term survival and competitiveness. In the context of a petrochemical industrial complex located in the port of Castellón (Spain), this paper primarily discusses whether such certifications – which act as signals of firms’ desirable environmental conduct – translate into higher trust in firms and lower risk perception by residents. Contrary to what might be expected, despite the widespread use by companies of voluntary and certified EMSs, the research findings confirm a relatively high citizen perception of risk regarding the industrial complex and a low trust in companies. On the other hand, the findings also show a low trust in the public institutions responsible for authorizing and monitoring firms’ activities and for enforcing possible sanctions in non‐compliance cases. Copyright © 2013 John Wiley & Sons, Ltd and ERP Environment