Threshold limit value In a welding shop, the measured concentrations of CO, CO2 and welding fumes are 10, 1,500 ppmv and 3.5 mg/m³, respectively, all below the recommended TLV-TWA. Is this working environment safe to the workers daily based on normalized concentration?

Question

Threshold limit value
In a welding shop, the measured concentrations of CO, [latex]CO_{2}[/latex] and welding fumes are 10, 1,500 ppmv and 3.5 mg/m³, respectively, all below the recommended TLV-TWA. Is this working environment safe to the workers daily based on normalized concentration?

Accepted Answer

TLV-TWA can be found in Table 14.2. And they are listed as follows

Table 14.2 Threshold values of typical indoor air pollutants in work places

Particulate pollutant		TWA (mg/m³, except for asbestos)
Asbestos		0.1 fiber/ml
Coal dust, anthracite		0.4
Coal dust, bituminous		0.9
Grain dust (Oat, wheat, barley)		4.0
Graphite (non fiber)		2.0
Iron oxide particles and fume, inhalable		5.0
Lead		0.05
Welding fumes		5.0
Gases	Formula	TWA (ppmv)	STEL (ppmv)
Ammonia	[latex]NH_{3}[/latex]	25	35
Carbon dioxide	[latex]CO_{2}[/latex]	5,000	30,000
Carbon monoxide	CO	25
Formaldehyde	HCHO	–	0.3
Hydrogen sulfide	[latex]H_{2}S[/latex]	10	15
Methanol	[latex]CH_{3}OH[/latex]	200	250
Ozone	[latex]O_{3}[/latex]	0.05–0.2	–

Sources ACGIH [11], WHO [7]

Pollutant	TLV-TWA	Measured concentration	[latex]C_{i}/TLV_{i}[/latex]
CO	25	10	0.40
[latex]CO_{2}[/latex]	5,000	1500	0.30
Welding fumes	5	3.5	0.70

Then the normalized concentration can be calculated as follows
[latex]C_{N}=\sum{\frac{C_{i}}{TLV_{i}} }=0.40 + 0.30 + 0.70=1.4\gt 1.0[/latex]

Since the [latex]C_{N}[/latex] > 1, it is not safe for the workers to be there daily (8 h).

Question 14.1: Threshold limit value In a welding shop, the measured concen...

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