|
Survey and health assessment of mercury in compact fluorescent lamps and straight fluorescent lamps 1 Introduction
1.1 Purpose and contentsFluorescent lamps are among the most efficient solutions available today to improve energy efficiency for home lighting (Wesnæs et al, 2009). Compact fluorescent lamps and straight fluorescent lamps contain, however, small quantities of mercury – and mercury is hazardous to human and the environment. The purpose of this project is to study whether there is a health risk associated with compact fluorescent lamps or straight fluorescent lamps that accidentally break in private homes. The study covers a survey of:
Furthermore a risk assessment (exposure and health assessment) has been made of mercury releases from broken fluorescent lamps. The project has been carried out with limited means and in a short period of time. Therefore it does not give a detailed study of all relevant aspects relating to compact fluorescent lamps/straight fluorescent lamps. 1.2 How do compact fluorescent lamps and straight fluorescent lamps work?Compact fluorescent lamps and straight fluorescent lamps consist of one or more bent or straight glass tubes with an electrode at each end. A compact fluorescent lamp is merely a more compact kind of a straight fluorescent lamp, where the tube has been integrated with the electrodes needed to start and stabilise the electric current through the tube. According to information received from manufacturers of compact and straight fluorescent lamps, lamps contain mercury either in the form of a HgFe tablet, amalgam[1] or as metallic mercury. Mercury is added with different dosage technologies in which the mercury is encapsulated in a tablet, a pill or as amalgam, or it is dosed as liquid mercury. Mercury in solid or liquid form is in equilibrium with vapour-phase mercury. Therefore, a small amount of vapour-phase mercury will be present in the lamp. In order for the lamp to work there must be a balance between the solid-phase and the vapour-phase mercury so that the atmosphere in the glass tube is saturated with mercury vapour. The glass tube/the container in a fluorescent lamp furthermore contain an inert gas (e.g. argon) under low pressure and the glass tube is coated on its inner side with a thin layer of fluorescent phosphor (www.datalyse.dk). When the glass tube is subjected to voltage the electrode is heated and electrons are released. The temperature in the tube increases and the mercury evaporates further. When the free electrons hit the mercury atoms the latter exite, i.e. are lifted to higher energy levels. Exited mercury atoms will decay after a certain time and thereby emit ultraviolet light together with a small amount of visible light. The ultraviolet light is converted into visible light when it hits the phosphor coating on the inner side of the tube (Aucott et al., 2003; www.datalyse.dk). According to information from one of the interviewed manufacturers some of the mercury will in its decay be bound to the glass and the phosphor coating. The amount of bound mercury will increase with the lifetime of the lamp. Normally this can be seen by the inner side of the glass and the inner phosphor coating turning grey. The areas near the electrodes will turn black with time. According to Truesdale et al. (1992) mercury will probably also be found in metal form in used compact fluorescent lamps/straight fluorescent lamps, since the inactive atmosphere in the tube should prevent significant oxidation of mercury. 1.3 Relevant legislation - RoHSAccording to the RoHS Directive 2002/95 (Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment) mercury in compact fluorescent lamps is exempted from the rule on a maximum content of 0.1 % in homogeneous materials. Maximum permitted mercury content in compact fluorescent lamps is 5 mg/lamp. For straight fluorescent lamps maximum permitted mercury content depends on the lifetime of the fluorescent tube and the type of phosphor coating on the inner side of the tube. For ”halophosphate”[2] permitted amount is 10 mg/lamp, and permitted amount of triphosphate[3] is 5 mg/lamp for normal lifetime and 8 mg/ lamp for long lifetime (RoHS EU, 2002). For compact fluorescent lamps and straight fluorescent lamps complying with European ecolabel criteria the mercury limit value is 4 mg/compact fluorescent lamp or 5 or 8 mg/straight fluorescent lamp depending on the lifetime (EU, 2002). See Table 1-1. Table 1-1 Maximum permitted content of mercury in compact fluorescent lamps and straight fluorescent lamps (RoHS EU, 2002), (EU, 2002).
All exceptions in the RoHS directive are now being revised and according to the Danish Environmental Protection Agency it is planned to lower the limit values for straight fluorescent lamps and compact fluorescent lamps. It is being discussed to lower the maximum permitted content of mercury to 3.5 mg Hg or maybe as low as 2 mg Hg for certain types of compact fluorescent lamps. 1.4 SummaryCompact fluorescent lamps and straight fluorescent lamps contain small quantities of mercury. Mercury that is hazardous to health is needed to make the fluorescent lamps give off light. In addition, fluorescent lamps contain an electrode, an inert gas and have a thin phosphor coating on the inner side of the glass. When electric current is induced to the lamp electrons are released exiting mercury atoms, which are lifted to higher energy levels. In the subsequent decay ultraviolet light is emitted and converted to visible light when it hits the phosphor coating on the inner side of the glass. During the lifetime of the lamp more and more mercury will be bound to the phosphor coating. Quantities of mercury in a fluorescent lamp are regulated in the RoHS Directive allowing no more than 5 mg of mercury per compact fluorescent lamp (and slightly higher values for straight fluorescent lamps). These values are being revised now, and work is ongoing to reduce the limit values for mercury contents in fluorescent lamps further. [1] Amalgam is a mercury alloy. An alloy is composed of one or more elements of which at least one of the elements is a metal. (Den Store Danske, 2009). [2] According to dataanalyse.dk the most common halophosphate compound is calcium fluorophosphate Ca5F(PO4)3. [3] According to dataanalyse.dk rare soil types and, often, four to five different phosphates are added to obtain better colour value.
|