Stephen Hardcastle & Kevin Butler CANMET – MMSL, Sudbury, Canada

1. A comparison of globe, wet and dry temperature and humidity measuring devices available for heat stress assessment Stephen Hardcastle & Kevin Butler CANMET – MMSL, Sudbury, Canada 12th North American/U.S. Mine Ventilation Symposium Reno, Nevada, U.S.A., June 9-11, 2008

2. Heat Stress Assessment • To control core temperatures …. • Most heat exposure regulations in Canada stipulate the use of the American Conference of Governmental Industrial Hygienists Threshold Limit Values and Biological Exposure Indices – Heat Stress and Strain documentation. • Depending on the version used, based upon a metabolic rate these can determine work-to-rest regimes and an action limit

3. Wet Bulb Globe Temperature WBGT(out) = 0.7tnwb + 0.2tg + 0.1tdb WBGT(in) = 0.7tnwb + 0.3tg Underground Mines WBGT Screening Criteria, ºC (2001) Note: decision differences range from 0.5 to 2.0ºC

4. Heat Stress Assessment Some of the issues …. • Preference for electronic instruments • Assumption precision = accuracy • Adequate accounting for air speed (using tnwb was a simplification to avoid measuring velocity) • “Wet” instruments not practical • “Dry” instruments more suited to long-term monitoring • Air density effects with depth

5. WBGT Instrumentation “Wet” Meters • Blackened Globe Sensor • Radiant Heat • tg Natural Wet Bulb Sensor - tnwb Ambient Dry Bulb Sensor - tdb Water Reservoir

6. WBGT Instrumentation “Wet” Meters measuring tnwb, tdb, tg WiBGeT RSS-214 Heat Stress Monitor (3M, formerly IST-AIM) QUESTempº34/36 Thermal Environment Monitor (Quest Technologies) Heat Stress SensorLynx Monitor (IST-AIM, no longer available) Microtherm Heat Stress WBGT Meter (Casella CEL) QUESTemp also measures %RH

7. Other Instrumentation “Dry” Relative Humidity Meters HSM, Heat Stress Monitor (Calor Instruments) tdb, tg, Humidity, Pressure, Velocity Kestrel 4000 Pocket Weather Tracker (Nielsen-Kellerman) tdb, Humidity, Pressure, Velocity HMI41/HMP45 Humidity Indicator (Vaisala) td, Humidity SmartReader Plus multi-channel data loggers (ACR Systems) td, Humidity, Pressure Calculates psychrometric wet bulb, twb or tnwb (Calor)

8. 0.2ºC Spread between sensors = 2 x 0.1ºC Resolution Casella Microtherm Dry Bulb Sensor Casella Microtherm “Dry” Wet Bulb Sensor Temperature Comparison Small Environmental Chamber with temperature and pressure controls Casella Microtherm “Dry” Globe Sensor

9. Temperature Comparison Unexplainable delay on dry and globe sensors

10. Dry Bulb tdb Sensor Response All show excellent linearity - gradients 1.0 - intercepts typically small All units generally agree

11. Wet Bulb Comparison Constant Dry Bulb Temperature 16ºC Transition/unstable data removed before regression analysis

12. Δtnwb  2.2ºC 10%RH Values Δtnwb  0.9ºC 60%RH Values Natural tnwb Sensor Response Data spread decreases as a function of %RH Group shows variable spread & “non”- linear performance

13. Natural Wet Bulb Sensors Findings • Previous testing showed sensors agree in “dry” state • Spread in values most likely a function of different evaporative characteristics • Assuming a “global” air velocity probably contributed to the lack of linearity across tests • tnwb calculations very sensitive to velocity at low air speeds • Sensitivity accentuated at low humidity • Different “non-Standard” configurations • Lack of adequate/confirmed/traceable theory

14. 12ºC Spread Delay function of size Globe tg Sensor Response Differing instrument response Outside Comparison Standard 150mm (6”) diameter globes

15. WBGT Meters Findings • All instruments can adequately measure dry bulb temperature typically agreeing within 0.5ºC • Globe and natural wet bulb sensors when “dry” agree with dry bulb sensor • Agreement of natural wet bulb sensors ranged from within 0.9 to 2.2ºC depending on %RH • Globe sensors disagreed by up to 12ºC despite all being corrected to the “150mm standard” • Uniform radiant heat calibration difficult • Wet and Globe measurements are not traceable back to a standard • Are “dry” instruments any better?

16. Calculated using moisture content from precision chilled mirror dew point meter Calculated using tnwb %RH Sensor Response Instruments “agree” Spread within specified accuracy Most show good linearity Agreement a function of accuracy Distinct response -10% ΔRH @ 50%RH Consistent difference +10%ΔRH

17. Δtwb 3.5ºC 10%RH values Vaisala ±2%RH QUESTemp ±5%RH 60%RH values Psychrometric twb response Lack of agreement and linearity a function of %RH The group showed a lack of agreement and differing linearity Some Instruments showed good agreement and linearity

18. Psychrometric Wet Bulb “Dry” Relative Humidity Meters • “Agreement” of humidity meters is a function of their calibration tolerance/quoted accuracy • Calibration tolerance directly impacts the resulting confidence of a twb determination • Meters typically use Standard barometric pressure 101.32 kPa • In deep mines at 140kPa, twb determinations could be underestimated by 0.4 through 1.4ºC depending on the humidity • Theory adequate to indirectly determine twb

19. Natural Wet Bulb “Dry” Relative Humidity Meters Indirectly determining tnwb, as used by the Calor HSM, appears to be more difficult: • It was not possible to establish what theory or relationship the Calor HSM employed • It had a different %RH response Due to the lack of adequate theory and traceability to a standard it was not possible to determine if such instruments could provide a natural wet bulb and hence a work to rest regime with acceptable confidence

20. Which Instrument ? “WBGT” Meters • Globe temperature measurement is typically redundant in Canadian mines – use dry bulb • Tests show a lack of agreement in tnwb - this may improve at higher airspeeds but it then starts to approximate to the psychrometric wet bulb = ≠ ≠ Discontinued • Meters show limited comparability across manufacturers

21. Which Instrument ? Psychrometers, Heat Stress or “WBGT” Meters • From the tests performed and instruments evaluated it was not possible to confirm that “dry” instruments could replace “wet” units ≠ ≠ • Apart from dry bulb temperature there was limited comparability across the type of instruments

22. Which Instrument ? Psychrometers • From the tests performed and instruments evaluated, dry bulb/relative humidity meters were the most consistent with verifiable performance • Well calibrated meters can be confidently used to provide the psychrometric wet bulb Supervisors $329(US) pocket meter Ventilation Staff $930(US)  Vaisala Kestrel • These units have been adopted by Vale Inco within their heat management procedure

23. Which Instrument ? Deep Mine Conclusions • WBGT instruments do not need any barometric pressure correction but confident usage remains an issue • The Kestrel 4000 and Calor HSM include suitable resolution barometer but their application is limited to 2000 & 1500m respectively • These, or similar instruments, require the manual calculation of the psychrometric wet bulb temperature

24. Acknowledgements: Deep MiningResearch Consortium Vale Inco Agnico-Eagle Ottawa University School of Human Kinetics