How do you choose Gas Detectors?
With such a vast array of gas detectors on offer, correct selection can be a major problem. This is in many instances not helped buy the companies offering them as they can be viewed as just another sale against their target. With that in mind buyers need to ensure they have a risk assessment that is detailed enough to ensure that what they buy will protect their workforce from what they will actually come up against. This means detailing exactly what the hazards are, so the gas cell selection will detect what you need it to.
This sounds all too simple, but I have lost count how many times we have been asked for gas detectors that would not detect their target gas or have cells that have cross sensitivity issues. This means that the cell may for instance may have been selected for chlorine but there is also hydrogen sulphide present. These cells are cross sensitive, so either gas can give a reading on them both if they are electrolyte cells. This may well still give a desired alarm and ensure worker safety, but this should be verified first.
The same problem exists with flammable detection cells. All too often we are told to calibrate for a particular gas such as methane, but the real hazard may be a different gas altogether as not enough background information has been given. The gas detector could then alarm too early, very preferable for safety, or way too late dependent on the gas that is there and in some instances not at all!
When alarms happen all too often the user feels that the unit will tell them exactly what the gas was. This again is in the main incorrect, the cells gives an electrical output which is displayed as the alarm. If this is for a flammable you may get an alarm but if the space has various flammable possibilities there is no way of knowing if that alarm level was safe or what the gas was. Or worse still you calibrated your unit for methane, because you think it will see all flammables and then expect it to see diesel which without the correct cell it will not detect. So you do need to supply the correct information at the start to end up with the correct selection for use.
The feeling that I get from the majority of the customers is that they think their gas detectors will always fail safe. Well unfortunately if you understand how gas detectors work you soon realize that this is not the case. This is why bump or function testing is so important and why each manufacturer states that it needs to be done on a regular basis in their instruction manuals. In the States it is enforced but how many customers outside of the US are told this when talking to the people that are trying to sell them gas detection? All gas detection cell suppliers allow for a 5% cell failure rate and they can also become poisoned if used in atmospheres with certain contaminants. All this can add up to your gas detector not seeing what you bought it to detect.
The safety factor has been further reduced with the disposable single gas market packaging and soon to come into play the disposable multi gas detectors. This packaging is often misleading and may state 2 year disposable gas detector with no requirement for calibration. Whilst the statement is very true, the packaging does little to enforce that bump or function testing is a vital requirement to ensure worker safety. Manufacturers when quizzed will state that this is included in their instructions, again true but how many really read the instructions.
This part is a failure of the employer as PPE legislation states that PPE must be suitable and regularly maintained with sufficient training given to the user to ensure its correct use. But this would be far easier if it was explained by the supplier at the time of purchase.
There are then the alarm settings, these are different from Country to Country with STEL's and LTEL's having different values. Even instantaneous alarm levels vary and they should be set correctly for the region you are in. Company's can have their own alarm level settings providing they offer increased safety, decreasing the safety setting of that Country is illegal. But you may end up with a unit like it if it has been supplied from outside your region. Readings the instructions details this and most units will display there alarm settings on the start up sequence.
There are many reasons these days why many of these points, can and are being missed. It can be a belief of a salesperson that the cost of the bump gas along with the regulator would decrease the number of units sold. It could be that the units have been bought on line for the lowest cost and there is no interaction between the supplier and the buyer and the supplying Country alarms are not the ones you require. Or have been bought via a brochure type Company, as a preferred supplier and the general list of equipment on offer is believed to cover what is required. The problem is, all of these solutions in fact only really cater to the seller and offer little or no interaction to ensure that the items are fit for purpose.
I believe that all PPE, gas detection included, should be arrived at through a specific risk assessment. After all when we are using PPE it is because we have accepted that we could not eliminate the hazard, otherwise there would be no requirement for it. So select your equipment carefully and understand exactly what is required as every life is important.