FormaldehydeFormaldehyde (fɔːrˈmældɪhaɪd , USalsofər- ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section Forms below), hence it is stored as an aqueous solution (formalin), which is also used to store animal specimens. It is the simplest of the aldehydes () and one of the simplest of the carbohydrates. The common name of this substance comes from its similarity and relation to formic acid.
Legionnaires' diseaseLegionnaires' disease is a form of atypical pneumonia caused by any species of Legionella bacteria, quite often Legionella pneumophila. Signs and symptoms include cough, shortness of breath, high fever, muscle pains, and headaches. Nausea, vomiting, and diarrhea may also occur. This often begins 2–10 days after exposure. A legionellosis is any disease caused by Legionella, including Legionnaires' disease (a pneumonia), Pontiac fever (a nonpneumonia illness), and Pittsburgh pneumonia, but Legionnaires' disease is the most common, so mentions of legionellosis often refer to Legionnaires' disease.
LegionellaLegionella is a genus of pathogenic gram-negative bacteria that includes the species L. pneumophila, causing legionellosis (all illnesses caused by Legionella) including a pneumonia-type illness called Legionnaires' disease and a mild flu-like illness called Pontiac fever. Legionella may be visualized with a silver stain or cultured in cysteine-containing media such as buffered charcoal yeast extract agar. It is common in many environments, including soil and aquatic systems, with at least 50 species and 70 serogroups identified.
Return periodA return period, also known as a recurrence interval or repeat interval, is an average time or an estimated average time between events such as earthquakes, floods, landslides, or river discharge flows to occur. It is a statistical measurement typically based on historic data over an extended period, and is used usually for risk analysis. Examples include deciding whether a project should be allowed to go forward in a zone of a certain risk or designing structures to withstand events with a certain return period.
