Step 4 : Evaluate Exposure (Inhalation, Qualitative MR)

Degree of Chemical Released

Through Observation

Degree	Observation
Low	• Low or little release into the air. • No contamination of air, clothing and work surfaces with chemicals. • Low volatility with the boiling point more than 150oC at room temperature (20oC). • Low dustiness such as pellet like solids that don’t break up. Little dust is seen during use e.g. PVC pellets, waxed flakes.
Moderate	Moderate release such as: a) Solvents with medium drying time* in uncovered containers or exposed to work environment; b) Detectable odour of chemicals. Check the odour threshold. • Medium volatility with the boiling point at 50oC to 150oC at room temperature (20oC). • Medium dustiness such as crystalline, granular solids. When used, dust is seen, but settles out quickly. Dust is left on surfaces after use e.g. soap powder. • Evidence of contamination of air, clothing and work surfaces with chemicals.
High	• Substantial release such as: a) Solvents with fast drying time* in uncovered containers; b) Sprays or dust clouds in poorly ventilated areas; c) Chemicals with high rates of evaporation exposed to work environment; d) Detectable odour of chemicals with odour threshold at/above PEL/ OEL. • High volatility with the boiling point less than 50oC at room temperature (20oC). • High dustiness such as fine, light powders. When used, dust clouds can be seen to form and remain in the air for several minutes e.g. cement, carbon black, chalk dust. • Gross contamination of air, clothing and work surfaces with chemicals.

Using Direct Measurement

Direct Reading Measurement Result	Degree
≥ PEL	High
≥ 0.5 PEL but < PEL	Moderate
< 0.5 PEL	Low

Degree of Chemical Inhaled

Degree	Observation
Low	• Low breathing rate (light work) • Source far from breathing zone
Moderate	• Moderate breathing rate (moderate work) • Source close to breathing zone
High	• High breathing rate (heavy work) • Source within breathing zone

Frequency-Duration Rating: (1)

Magnitude Rating: (3)

Exposure Rating: 2

Frequency-Duration Rating	Magnitude Rating
	1	2	3	4	5
1	1	2	2	2	3
2	2	2	3	3	4
3	2	3	3	4	4
4	2	3	4	4	5
5	3	4	4	5	5