Types of hazards

Some items are hazardous by nature, while others only become hazardous if used inappropriately or carelessly. Often, accidents don’t just happen – they are a result of workers neglecting or ignoring hazardous situations. There are two basic categories of hazard: Acute hazard Acute hazards are those that have an obvious and immediate impact. Chronic hazard Chronic hazards have a more hidden, cumulative, long-term impact. An example of an acute hazard is a slippery floor where there is an immediate danger of someone slipping and being injured. A chronic hazard could be workplace bullying, where the long-term impact may result in stress or other psychological injury. Hazards generally fall into one of six groups: Physical – Slippery floors, objects in walkways, unsafe or misused machinery, excessive noise, poor lighting, fire. Chemical – Gases, dusts, fumes, vapours and liquids. Ergonomic – poor design of equipment, workstation design, (postural) or workflow, manual handling, repetitive movement. Radiation – Microwaves, infra-red, ultraviolet, lasers, X-rays and gamma rays. Psychological – Shiftwork, workload, dealing with the public, harassment, discrimination, threat of danger, constant low-level noise, stress.

Why oil return in refrigerant

The oil return in refrigeration systems is of key importance for the service life of the compressor and thus for a secure constant supply of refrigeration. In most compressors some lubrication oil is carried along with the compressed refrigerant. In the liquid refrigerant the oil is dissolved in the refrigerant and is transported without problems. In the vaporised refrigerant the oil remains liquid in the lower parts of the system. This can result in lack of oil in the compressor. To return the oil to the compressor, a minimum velocity must be maintained in the pipes. If the velocity in the rising pipe on the intake side of the compressor is too low (partial load), the oil is not returned to the compressor due to its higher density. The velocity in the rising pipe depends on the pipe diameter and the refrigerant mass flow. A small diameter of the rising pipe results in a high velocity and ensures the return of the oil even under partial load. However, at full load the pressure loss increases due to the small diameter. To compensate for this disadvantage, double rising pipes are used. During partial load oil gathers in a bend at the bottom of the double pipe. The oil in the bend blocks one of the two pipes so that the refrigerant flows at high velocity through the other pipe and transports the oil to the compressor. At full load the oil in the bend is pressed upwards so that the refrigerant flows through both pipes. Mohammad Imran HVAC Engineer