Reducing risk with Exposure Monitoring Equipment

What we know What we don’t know What we must assume What we must never assume Components of risk assessment What is the conclusion of risk assessment? The definition of acceptable risk

PID and LEL monitors Do they keep you safe?

These machines are DUMB! The value displayed is a TOTAL concentration of all DETECTED compounds AS IF (selected compound) Indicative at best

Calibrate to Chocolate: Display 500 Chocolate Display Vanilla (response factor 8): 4000 Vanilla Display Cake (response factor 0.002): 1 Cake 300 Chocolate (RF 1) 200 Flour (RF 0.25) 200 Sugar (RF 0.47) 6 Cocoa (RF 1.16) 150 Sunflower oil (RF 0.1) 300 Soured cream (RF 0.08) 2 Egg (RF N/A) 1 Vanilla Extract (RF 8)

PID : Photo Ionisation Detector Broad spectrum Sensitive Non destructive Low cost Cannot see smaller/lighter compounds e.g. methane UV Lamp ionises the gas sample. The free electrons are then counted and this value is converted and displayed as gas concentration (typically in ppm).

LEL and close space monitors Lower Explosive Limit Catalytic diffusion sensor burns available volatiles and converts the energy value to display %LEL Broad spectrum Low cost Can detect smaller/lighter compounds (methane) O 2 H 2 S CO LEL

%VOL - %LEL - PPM EXAMPLE: Pentane 1%VOL―75%LEL―10,000ppm 1%LEL―0.13%VOL―133ppm 1ppm―0.0075%LEL―0.0001%VOL Typical resolution for LEL monitors 1.0%LEL Typical resolution for PID 1ppm Best resolution for PID 1PPB!

Correction factors: Calibration gas and Action alarms Correction factors are not absolute Sensor type/manufacturer Calibration gas:  Pentane/Methane?  Isobutylene? Are alarms preset? Is this arbitrary?

Other factors Weather conditions Sensor inhibitors: Methane, Nitrogen, Carbon monoxide Sensor poisoning: Silicones Sensor reaction time: Pentane/methane Personal proximity

ZERO Nominal drift Who do you trust? Warm up period Ambient or absolute? Carbon filter

Bump testing and Calibration Ensure adequate warm up period Pump stall test Bump test first Potential issues: No gas, blocked regulator, cold machine, contaminated filters, incorrect gas selection When to calibrate? Potential issues: as above Gain?

Are these machines DUMB? It is not the tools we use which make us good, but rather how we employ them. These tools help you to redefine the risk and revaluate your own acceptable risk