At a surface mine office the independent Sound Pressure Level (SPL) measured in dB(A) on account of 3 drill machines are 85,88 and 85. If all the three machines work simultaneously, the combined SPL, in dB (A) is

How the anemometer is used to determine the average velocity of air?

A. Anemometer should be moved throughout the cross section of the roadway

B. It is kept at the roof of the gallery

C. It is laid at the floor of the roadway

D. It is moved along a straight line

The important gaseous pollutants, contributing to acid rains, are

A. SO₂ and NO_x

B. CO₂ and H₂S

C. NO_x and O₃

D. None of the

The delay between the ignition and the application of the heat source termed as

A. lag on ignition

B. incubation period

C. saturation period

D. thermal conductivity

A high volume air sampler is operated for 8 hrs in a mine with the flow rate of air varying from 1.5 m³/min to 1.3 m³/min. The empty weight of the filter paper is 2.30 g and the final weight is 2.65 g. The mean concentration of the suspended particulate matter (SPM) during the study period in μg/m³ is

A. 591

B. 550

C. 545

D. 521