I start with a confession. In my youth (before the children and grey hair) I worked for Van Walt Ltd in the UK. Before I had completed my first month of employment I had been issued my first written warning… by my own father…

At Van Walt we have a number of monitoring wells installed in the premises for demo, training and test purposes. One afternoon I was using one of these monitoring wells to familiarise myself with our Advanced Peristaltic Pump and Flow Cell arrangement. Vincent came out to check on me and the following conversation ensued:

Vincent: what are you doing?
Me: using the peristaltic pump.
Vincent: Yes, I can see that … WHY ARE YOU SMOKING A CIGARETTE!!!!!?
Me: Errr
Me: Errrrrr
Me: Ummmm…
Me: Ahh…
Vincent: Office … NOW!
Me: Oh heck!…

I won’t bore you with the details of the lengthy dressing down I received that afternoon but suffice to say I am much more safety conscious these days … (although there was the incident with the fixed blade knife at URS’s office in Christchurch … I’ll tell you another time).

I do remember foolishly arguing the fact that I was in the office car park and there was no danger of contaminants or explosion … Looking back I am in awe of the old man’s composure and restraint at that moment. I don’t believe the anti-smacking law existed back then and frankly I am lucky to be writing this today with my good looks (matter of opinion) still intact.

Anyway, I digress. The point of this story is that we do not know for sure the history of any plot of land. Indeed, the fact that we/you are there taking samples in the first place suggests there is something there that should not be. So keeping safe on site needs to be taken seriously.

Enter modern technology and, specifically, PIDs and LEL monitors. Most of you will know that Van Walt Ltd has supplied PID monitors as part of our Groundwater rental fleet for some time now. PID technology is ideal for broad spectrum analysis of airborne compounds. It can be a useful sampling tool but more importantly can keep you safe onsite by monitoring the air quality. For more information on PIDs take a look HERE.

The perfect complement to PID technology for keeping you safe is the LEL monitor (now available to rent in Spain and the UK (and for some time already in NZ). The reason why the two units are a match made in heaven is that LEL technology can smell/burn compounds that PIDs cannot. PIDs cannot ‘see’ smaller hydrocarbon compounds like Methane, Ethane, Acetylene and (naturally) Hydrogen. You may spot the common property with these compounds – they are flammable/explosive.

As a general rule – if it burns the LEL monitor can detect it – and therefore give you advanced warning before concentrations reach dangerous (explosive) levels. Keeping you much safer onsite.

A quick recap on the term LEL (Lower Explosive Limit). LEL monitors display flammable compounds (again broad spectrum like the PID) as a percentage of LEL. For example: The lower explosive limit of Methane is (about) 5% by VOLUME (any less than this and there is simply not enough methane to react with available oxygen and combust). Therefore if there were 2.5% volume of methane in the air, the LEL monitor would display 50% LEL.

DO NOT FORGET! Just because the monitor says there is only 20% LEL, IT DOES NOT MEAN that concentrations a few feet away are the same.

Methane or Pentane? Like PID technology, every compound has a response factor relative to the calibration of the unit. Gasoline has an approximate response factor of 0.5 against a methane calibrated LEL monitor. That is to say, if the monitor displays 50% LEL there is already 100% LEL gasoline and you should be running very fast in the other direction!

For those of you onsite where you suspect petroleum hydrocarbons, we can calibrate your LEL monitor to PENTANE. Pentane has approximately the same response factor as gasoline and so should keep you safer onsite. In this configuration if there is Methane present the monitor will overstate the concentrations (which is more acceptable than the other way around).

In some cases a response factor can be input to the LEL monitor. In this way a methane calibrated monitor can be set to display ‘AS IF’ Pentane. BE AWARE that although the response factor may be correct, heavier/larger hydrocarbon compounds do not filter as easily through the LEL sensor. This can cause the monitor to understate its readings. It is always better to calibrate the unit to the closest match available to the compound you are concerned with.

Lecture over! Stay safe out there and stay away from folding pocket knives!

Dirk van Walt