Calculations and essay questions
Word guide: 3000 word maximum for Q1
To assess your ability to:
• demonstrate a detailed understanding of the principles of measurement of the thermal environment, lighting and noise
• demonstrate an understanding of the key principles and basic concepts of occupational hygiene by considering the future challenges for the discipline of occupational hygiene
• demonstrate an understanding of the principles of ventilation and calculate adequate volume flow rates
• determine whether noise levels in a particular situation are excessive
1. Essay questions
A) Explain and discuss why the demands of the tasks undertaken in the workplace need to be considered when conducting assessments of the thermal and visual environments.
B) Explain and discuss the different reasons why it may be important to analyse the frequency composition of a noise source.
C) What are the challenges for occupational hygienists in the future in terms of changing workplaces and workforces? Discuss.
[Ensure that the points made in your essay are relevant to the key components of occupational hygiene practice]
A small printing business has introduced a new process which transfers designs onto fabric. An occupational hygienist is brought in to investigate whether the existing ventilation system is adequate and whether additional noise controls are needed. Complete the following calculations:
Inks for the printing process contain 20% by volume of solvents. The mixture, by volume is: 40% n-hexane, 20% methyl ethyl ketone (MEK), and 40% toluene. During the print run, ink is used up at the rate of 6 litres per hour. The air inlet hood has a face area of 0.20m2 and an air inlet velocity of 0.5 m/s.
Is the air flow rate adequate for dilution of the flammable vapours released by the process? [Use a safety factor of 4 and a temperature of 20°C]
Q’ = 22.4 (273 + T°C x SG x V x K x 102
273 x 3600 x M x C x B
Component Specific Gravity(SG) Molecular Weight (M) LEL (%)
n-hexane 0.66 86.17 1.18
MEK 0.805 72.10 1.81
toluene 0.866 92.13 1.27
i) An indoor fan with a sound power level of 94dB is to be installed at the centre of one wall of the room. As sound pressure levels vary according to the presence of reflecting surfaces, what would the sound pressure level at 3 metres be?
ii) Estimate the noise attenuation outdoors if the noise level at 40m from rooftop machinery is 88dB in the 500Hz band and 94dB in the 4000 Hz band. What is the noise level in each band at a distance of 1000m?