What is an Airflow Indicator?

What are Airflow Indicators and do I need to fit them? 

Airflow indicators come in different types, shapes, sizes and even names.

Some refer to them as indicators, whilst others like to call them gauges and sometimes the preference is as monitors.

Whatever they are called, they all should be designed for use with LEV systems to provide a visual indication of the system performance, ultimately protecting the workforce.

Do I have to fit Airflow Indicators?

Airflow indicators, definitely cannot be considered as a new topic.  After all they have been on the HSE’s radar for some time, from when they have formed part of what the HSE would consider a CoSHH approved code of practice.

Nevertheless, they are an ever present point of enquiry.  Not a day goes by without someone asking some question or other about ‘airflow-indicators’.  Much of this, we believe, is due to the mixed messages out there.

Statements like ‘it’s the law!’, ‘I’m only a small business, so it doesn’t apply to me?’, ‘I’ve been told that if I don’t fit gauges that I will be fined!’, ‘I rarely use my system and so I don’t need to carry out any checks’ and so on.

Although the HSE provides a good reference tool, especially within the ‘local exhaust ventilation’ section of their site they don’t really provide clear instruction on the subject : “there isn’t a specific legal requirement to have airflow indicators fitted to an extraction.  But as an employer you do by law have to make sure that your LEV system keeps working properly”.

This might all sound a little woolly.  There either is or there isn’t a legal requirement?

Well in considering their statement, the second part is the key section, in that there is a legal requirement to ensure that your local exhaust ventilation system is working properly.

An assumption has been made that there is a broad understanding of what is meant by LEV (local exhaust ventilation), so to save any confusion the writer considers it to be an engineered system of control to protect employees by minimising exposure to hazards (dust, fume, gas, mist and vapour) substances by capturing the contaminant at source and exhausting at a safe point (either to atmosphere or to a filters, subject to the contaminant).

How do you make sure that your local ventilation system is working properly?

The HSE publications CoSHH ACoP and HSG258 contains instruction, guidance and recommendations relating to the installation and use of airflow indicators including:

The Control of Substances Hazardous to Health Regulations 2002 (as amended) Approved Code of Practice and guidance

Page 32 : Guidance 7 – Para 113 : “The effectiveness of control measures should be checked regularly.”

Page 42 : APoC 8 – 167 : “Employers should establish……visual checks and observations at appropriate intervals; monitoring systems for the effectiveness of controls and prompt remedial action where necessary.”

Page 45 : APoC 9 – 182 : “Condition monitoring, e.g. air flow sensors in extraction ducts, may need to be continuous and linked to alarms.”

Controlling airborne contaminants at work – A guide to local exhaust ventilation (LEV) HSG258

Page 8 : 15 : “When applying LEV employers should be aware of: the need for airflow indicators and other instrumentation;”

Page 23 : 74 : “The employer: should require indicators to be fitted to show that the system is working properly;”

Page 23 : 77 : “To get what you need and avoid any misunderstanding with the LEV supplier it may help to ask your supplier to: describe the indicators and alarms to be provided in the system;”

Page 27 : 86 : “The value of monitoring the performance of the hood, e.g. by using an airflow indicator.”

Page 32 : 106 : “Employers should make sure that LEV systems continue to work properly. There are several ways of checking this, such as using an anemometer, dust lamp or smoke tracer – with the work process running. The simplest way is probably to use an airflow indicator. This will give the operator a simple indication that the hood is working properly. It becomes critical when the operator has to adjust a damper to get adequate airflow. The airflow indicator must indicate simply and clearly when the airflow is adequate. The simplest indicator is usually a manometer. (Also see ‘LEV instrumentation’ in Chapter 7.)”

Page 63 : 228 : “Users of LEV systems, particularly the operators at LEV hoods, must be able to tell that the hood airflow is still adequate to control exposure. Good practice requires the periodic monitoring of performance for all hoods. The designer should therefore specify suitable monitors such as manometers or other airflow indicators.”

Page 63 : 229 : “Airflow indicators cover a wide range of equipment: a simple and reliable device such as a manometer connected to the hood duct. The static pressure is a direct indicator of the airflow rate; a complex device, e.g. a pressure switch to activate an alert if the flow drops below pre-set trigger levels”

Page 69 : 252 – Table 14: “Locate airflow indicator near the plenum duct”

Page 70 : 256 – Table 15: “Provide airflow indicators, e.g. manometers, at hood ducts and at other necessary points”

Perhaps the clearest instruction is contained within the preface of the ACoP where it is stated that the ACoP has a “special legal status” and that it “gives practical advice on how to comply with the law” and “if you follow the advice you will be doing enough to comply with the law”.

There seems little point in not following the provisions of the code, especially as “if you do follow the guidance you will normally be doing enough to comply with the law. Health and safety inspectors seek to secure compliance with the law and may refer to this guidance.”

So hopefully, if there was confusion, this goes some way to providing clarification and an understanding that although ‘there isn’t a specific legal requirement’ there is a wider legal obligation (as stated throughout HSE publications) that the effectiveness of LEV control measures must be regularly checked and as such airflow indicators are prescribed as a reasonably practicable, best practice, method of assessment.

What types of Airflow Indicator should I use?

The choice of indicator is dependent upon the level of risk the process posses.

For low risk processes a basic analogue gauge should be sufficient.  While applications with more hazardous materials can demand more sophistication in the form of a more complex instrument, potentially providing an alarm or even control intervention.

Whichever type of equipment is used it is important that they provide a clear and uncomplicated representation of the system performance.

This doesn’t mean that the indicator has to be endorsed by NASA or require hadron collider levels of investment, rather it just needs to be effective, adequate and suitably robust for the application.

Unfortunately there isn’t a simple mechanism to demonstrate return on investment for airflow indicators and so it is hard to justify spending more on an electronic device than a simple gauge if your process is low risk.

Nevertheless simply looking at the initial capital expenditure might not tell you which the best device is.  Assuming that the all devices under consideration provide you with the same level of indication you should consider what the estimated serviceable life is and also what other ongoing cost there might be.  Both electronic and analogue devices will need some form of routine inspection or perhaps even calibration.

How do I correctly install Airflow Indicators?

Even a simple device can be incorrectly installed.

Anyone undertaking the installation of airflow indicators must be ‘competent’, as far as understanding LEV best practices and principles of design.

Any airflow indicator can be fitted inappropriately both in terms of correct flow (turbulence, blockages or isolation) and ease of operator reference.

Typically analogue gauges come with a present range of measurement, so it is important to understand what the duty of your system is.  A gauge with too low a range will show an overflow and a gauge with too wide a range will give a narrow point of reference.

Analogue gauges require set-up and commissioning, with zones (normally red : inadequate and green : adequate) set according to the system design.

It is not uncommon to see LEV installations with gauge ranges which are inappropriate for the system pressure and/or have the incorrect red and green regions.

Electronic gauges may be a better solution, as often they often cover a broad range of measurement, nevertheless they will still require correct installation, calibration and often run on batteries.

Some electronic gauges also only indicate the flow of air rather than displaying over and under pressure situations.

Part of a Broader Picture

Now you have airflow indicators installed, that doesn’t mean that you can simply rely on the feedback from operatives viewing the indicators to determine that the LEV control is adequate for the process.

You do have a legal requirement under the CoSHH (Control of Substance Hazardous to Health) Regulations 2002 to ensure that measures you use to protect employee’s health, in the form of extraction systems (LEV) are maintained in efficient and effective working order.  You must also have periodic thorough examination and testing of the LEV controls, at least every 14 months (the frequency can be less, depending upon the materials and processes undertaken).

As mentioned the HSE website in a great resource, containing plenty of reference material and guidance.  Although what better way of understanding the explicit requirements around airflow indicators and wider LEV health and safety issues than to chat with one of our impassioned experts?