Electricity, protective means insulation

The arc lamp C is attached by metal clips to the hollow support tube F which also allows flushing of the lamp area by nitrogen via inlet G and outlet H. The support tube F, the electrical leads to the arc lamp (not shown) and terminals for the cable from the power control unit (also not shown) are all attached to the terminal block J which is fitted with an insulating cover. The terminal block is attached to the inner quartz jacket by means of a rubber sleeve K and two sleeve clips, so that all the live parts are protected. The lamp and inner quartz jacket B can be withdrawn from the 40/38 socket attached to the outer quartz jacket A shown, and the entire unit can be withdrawn from the central socket of the reaction flask. 

Assuming that the protection system consists of a combination of coating and cathodic protection, the required current for protection is multiplied by the coating breakdown factor, /j, which is the anticipated reduction in cathodic current due to the application of an electrically insulating coating. Total initial, average, and final current will be adjusted with the initial, mean, and final coating breakdown factors,and/jp, respectively [4], Total initial current ... 

The accidental or unexpected starting of electrical equipment can cause injury or death. Don t work near any part of an electric power circuit that you could contact during your work, unless protected against shock by de-energizing the circuit and grovmding it or by guarding it effectively by insulation or other means. 

A further problem relates to encapsulation. The ion-sensitive gate area is exposed to the analyte solution, but all other parts of the sensor must be insulated from the solution. In most cases encapsulation is carried out by hand using epoxy resins, but it is impossible to produce ISFETs at low cost by this technique. Both photolithographic methods [159], [160] and an electrochemical method [161] have been proposed for the solution of this problem. One very promising development is the backside-contacted ISFET [162]. TTie electrical contacts in this case are protected from the analyte solution by means of O-rings, thereby circumventing the need for resins. 

The majority of fixed apparatus is of Class I construction, as defined in BS 2754 1999 Construction of electrical equipment for protection against electric shock. This means that it usually has a metal case enclosing the live parts and that the five parts are insulated from each other and from the carcass by basic insulation only. The case, which is earthed by connection to the protective conductor, protects the internal wiring and components from damage and prevents direct contact. 

Elecric shock as a result of direct contact, means that a person makes contact with part of the circuit which is intended to be live. The only form of protection against direct contact is to prevent such contact in the first place. This can be achieved by following the same principles of risk assessment and machinery safeguarding discussed earlier, namely to provide fixed guards, enclosures or insulation. However, if access is foreseeable, then permit-to-work systems should be operated. It should be remembered that intrinsic safety is an absolute priority in removing the risk of shock injury. This can be achieved by reducing the system voltage in areas of likely contact to such an extent that it cannot result in an electric shock. 

---