GROUP DISCUSSION

INTRODUCTION

The term ‘Engineering Controls’ covers a broad spectrum of possible interventions that are intended to reduce worker exposure, to chemical, physical and biological agents. This article will explain what ‘Engineering Controls’ are with respect to chemical and biological agents and how they fit into the hierarchy of controls. Examples are given of engineering controls along with some advantages and limitations. The importance of matching the control measure to the health risk and its reliability is also discussed along with commissioning. Once control has been achieved the article will explain why maintenance and checks are vital in order to maintain good control and therefore reduce worker exposure.

Definition

In the context of health and safety, an ‘Engineering Control’ can be described as a physical modification to a process, or process equipment, or the installation of further equipment with the goal of preventing the release of contaminants into the workplace. As can be seen from this broad definition there are a wide range of engineering controls, which could be applied. The control selected will depend upon the type of process, the nature of the contaminant source (its toxicity and release mechanism) and the route of exposure (inhalation, dermal, and ingestion). However, the reality is that no single engineering control in isolation will be successful; control is always a mixture of equipment and ways of working.

The Hierarchy of Control

The approach to controlling the chemical risk released from a process is rarely straightforward as there will always be a choice of control options – some easier to apply than others. However, the approach taken should be based on a priority list. This principal of priority is often referred to as the ‘Hierarchy of Control’. The European Control Hierarchy, as stipulated by Council Directive 98/24/EC gives the priority order and is summarised below

1. Elimination of hazardous substances
2. Substitution by a substance less hazardous 
3. Design of appropriate work processes and engineering controls and use of adequate equipment and materials, so as to avoid or minimise the release of hazardous chemical agents which may present a risk to workers' safety and health at the place of work
4. Application of collective protection measures at the source of the risk, such as adequate ventilation and appropriate organisational measures
5. Where exposure cannot be prevented by other means, the application of individual protection measures including personal protective equipment (PPE).

The directive goes on to state that hazardous chemical agents shall be eliminated or reduced to a minimum by

• the design and organisation of systems of work at the workplace
• the provision of suitable equipment for work with chemical agents and maintenance procedures which ensure the health and safety of workers at work
• reducing to a minimum the number of workers exposed or likely to be exposed
• reducing to a minimum the duration and intensity of exposure
• appropriate hygiene measures
• educing the quantity of chemical agents present at the workplace to the minimum required for the type of work concerned

 It should be noted that this hierarchical approach is not unique to Europe and is adopted by safety professionals worldwide. From the above list it can be seen that engineering controls are integrated into steps 1 to 4. For example it can be argued that modifying a manufacturing process so as to eliminate the hazardous substance is a form of engineering control. However, it is common practice to associate engineering controls with steps 3 and 4: i.e. once elimination and substitution of chemical hazards have been considered. At times engineering controls may not offer adequate control and may need to be supplemented with other measures. Often this will take the form of PPE, which includes respiratory protection equipment (RPE). As can been seen from the priority list, PPE is the last step if all other interventions fail to offer sufficient protection. The problem with PPE is that it only protects the wearer. For RPE this is of particular concern as whilst the process operator may be protected from an airborne hazard, once it is released into the air it will inevitably pervade the workplace and therefore expose others who are likely to be unprotected. Furthermore for RPE to be effective it needs to be properly selected and correctly fitted, making training and user cooperation essential.

Types and Examples of Engineering Controls

Process/Exposure source	Engineering control	Additional procedural control
Cleaning with solvent on rag	·        Use a rag holder ·         Provide a small bin with a lid for used rags.	·         Check controls are used ·         (ii) Safe disposal of waste
Dust spills from damaged sacks	·         Portable vacuum cleaners with HEPA filter	·         Ensure vacuum is maintained and available for use ·         Safe emptying of vacuum cleaner
Cutting-fluid mist from a lathe	·         Put an enclosure around the lathe and extract and filter the air and discharge to a safe place (Protective gloves will also be required)	·         Check and maintain fluid quality ·         Test and maintain controls
Dust from disc cutter on stone worktop	·         Carry out the process in an enclosure fitted with extraction, filter and extract to a safe place	·         Test and maintain controls ·         Train workers
Transfer of volatile liquids	·         Pumping rather than pouring ·         Tight fitting lids to minimise evaporation	·         Regular checks and maintenance (e.g. Check for damage to lids seals)
Evaporation of liquid from an electroplating tank	·         A layer of plastic balls floating on the surface to reduce both evaporation and mists	·         Check and maintain controls

Ensuring that Engineering Controls are effective and reliable

Why engineering controls often fail to protect workers

Engineering controls can fail for a variety of reasons. Often they are not as effective as envisaged and therefore fail to protect from the date they are installed. Even when initially effective their performance can gradually decline. This can be exacerbated by poor management, e.g. inadequate training. Therefore there are issues to consider in ensuring controls work effectively and go on working.

Commissioning

Once a control measure is designed and installed it needs to be commissioned. ‘Commissioning’ is proving that the engineering control is capable of providing adequate exposure control. The type of commissioning and the complexity depends upon the control measure. Probably the most complex commissioning process is that of LEV systems. Unfortunately LEV commissioning is frequently carried out incompletely or is inadequate. LEV commissioning tends to focus on the engineering parameters, such as system pressures and air velocities. Whilst this is an essential part of the commissioning process, a judgement on the effectiveness of the controls and the worker exposure needs to be taken. There are a number of qualitative and quantitative tools available to help the assessor judge control. An example of a qualitative assessment is the use of smoke tubes to visualise the air flow in and around an LEV hood in order to assess LEV performance. An example of a quantitative control is personal sampling to quantify worker exposure to a particular substance(s).

Worker Training

In isolation, an engineering control solution is destined to fail. They need to be integrated with other control measures, such as a ‘standard operating procedure’. It is highly likely that some form of training and supervision will also be required to ensure that the controls are correctly used and therefore control workers’ exposure.

Checks, Monitoring and Maintenance

Without regular checks and routine maintenance, the effectiveness of engineering controls will degrade gradually and inevitably fail. The time it takes for this to occur will depend upon the type of control measure. Engineering controls tend to degrade slowly with time and this often goes unnoticed. An example of this are poorly maintained LEV systems; often the workers can hear the fan impeller rotating, but do not realise that the volume flow rate of the system is imperceptibly falling with time resulting in a loss of control of the airborne contaminant. In this example the performance of the LEV hood could be continually monitored by the use of an air flow indicator, such as a pressure gauge.

Conclusion

All too often when companies realise they have an exposure problem, they immediately assume PPE is the only solution. Invariably this is not the case, and following the hierarchy of controls, engineering controls that are properly commissioned and maintained play an important role in reducing the workers exposure to the chemical risk in the workplace.

References

https://oshwiki.eu/wiki/Engineering_controls#Designing_and_Implementing_Engineering_Controls