Obiter Dictum: Remarks made by judges in the summing up of a case which are ‘by the way’ and not essential elements of the decision itself. These remarks often become persuasive precedents depending upon the seniority of the judge but they are not part of the ratio decidendi.
		Objective Measures: Performance measures which are detached from the observer’s personal judgement eg existence of ‘X’ in fact.
		Obstructive Airway Disease: See Occupational Asthma
		Occupational Asthma: A disorder of breathing characterised by a narrowing of the airways due to swelling of the airway wall. The condition is triggered by occupational exposure to allergens and some chemical substances.
		Occupational Exposure Limit: A level of exposure expressed as a WEL which is used to determine the adequacy of control of exposure by inhalation in the workplace. OELs are specified in official guidance EH40.
		Occupational Hygiene: The practice of recognition, measurement, evaluation and control of occupational health risks.
		Occupational Hygienist: One who practices occupational hygiene.
		Octave Band: The division of the frequency range of noise into bands with the upper frequency of each band being twice that of the lower frequency.
		Octave Band Centre Frequency: The frequency at the centre of an octave band. Used as a point in the measurement of noise.
		OEL: Occupational Exposure Limit.
		Off The Job Training: Training which takes the trainee away from the distractions of work activity into a formal classroom environment.
		Official Journal: Official journal of the European Union in which a directive is published once it has been adopted.
		Off-line Processing: The mental simulation of the choices open to us and their possible outcomes which has the disadvantage that we sometimes fail to consider properly all the options, or may not have sufficient information to enable us to make a choice.
		Ohm's Law: The potential difference between the ends of a resistance (or conductor) is directly proportional to the current flowing - assuming constant temperature. This relationship is given by the equation: Voltage = current x resistance.
		Oil Acne: Skin infection developing from plugged pores which become infected and produce blackheads and pustules. Dirty work involving mineral oils can lead to its development particularly on forearms and thighs.
		On The Job Training: Training which takes place in the workplace at the trainee’s workstation usually whilst engaged in normal duties.
		On-line Processing: Moment to moment decision making which requires little analysis of the outcomes but has the disadvantage that an inappropriate choice may be made on the spur of the moment.
		Open Face Head: Sampling head which accommodates filters of 25 and 37 mm diameter for sampling general or ‘nuisance’ dusts where high concentrations of larger sized particles are expected. Open face with cowl is more likely to be seen sampling for asbestos. The cowl protects the face of the filter and gives even distribution of airflow.
		Open System: A system that interacts with and depends upon exchanges with its environment. A flexible and adaptive system.
		Operant Conditioning: A learning process observed by Skinner in which appropriate or desired behaviour is rewarded when it is observed thus making it more likely that the behaviour be repeated.
		Optical Radiation: Electromagnetic radiation comprising ultraviolet, visible and infrared radiations.
		Organisation: The arrangement of human and physical resources based upon the need to control and integrate the activities of individuals and groups.
		Over Three Day Injury: A notifiable injury which causes absence from work or the inability to perform normal duties for a period of more than 3 days excluding the day of the injury but including rest days (RIDDOR).
		Overhead Travelling Crane: Overhead (or gantry) cranes run on tracks which span the workshop. They are often capable of withstanding high stresses but all of the components must be taken into account when assessing strength. This includes the tracks on which the crane runs and the points at which they are fixed to the building structure.
		Oxidising Agent: A chemical substance which promotes a combustion reaction when mixed with a combustible material.
		Ozone: A form of oxygen gas which occurs naturally in very small quantities in air. Most of the ozone is in the stratosphere where it forms the ozone layer.
		Ozone Detector: A direct reading instrument unique to ozone which works on the principle of chemiluminescence. Air is drawn into a reaction chamber where the ozone (if present) is reacted with ethylene. The product of this is in a high energy state and rapid return to its ground state occurs with the emission of light. This emission is amplified and measured.

Disclaimer:
Whilst every effort has been made to ensure the accuracy of the information contained in this book opinions may vary regarding some concepts. The Key Consultancy Ltd and Safety and Health Practitioner accept no responsibility for any loss arising from reliance on this content and readers should take steps to verify interpretations to their own satisfaction if there is doubt.