Book - School of Science and Technology

Air change rates 345Table 13.4 Limiting values of some common contaminantsExposure limit (ppm)Exposure limit (ppm)Contaminant 8 hour 10 min Contaminant 8 hour 10 minAcetone 750 1500 Hydrogen peroxide 1 1.5Ammonia 25 35 LPG 1000 1250Bromine 0.1 0.3 Methanol 200 250Butane 600 750 Nitrous oxide 100 ±Carbon dioxide 5000 15 000 Ozone 0.1 0.3Carbon monoxide 50 300 Sulphur dioxide 2 5Carbon tetrachloride 2 ± Trichloroethane 100 150Chlorine 0.5 1 Turpentine 100 150Formaldehyde 2 2 White spirit 100 125NoteThese data are presented to illustrate the wide range of limiting values. Reference in practice should be made in all cases to thecurrent edition of the Health and Safety Executive publication Occupational Exposure Limits, EH 40/± which is published annually.Air change ratesWhere the occupancy is unknown or variable, an arbitrary basis for the ventilation ratemust be taken. Table 13.5 may be used as a guide but the cubic content of the space andthe length of time for occupation may have an effect upon the rate of air supply necessary.For example, the air volume of a very large hall might be considered as holding a `store'Table 13.5 Ventilation based on air change ratesType of enclosureAir changesper hourVentilation Allowance(W/m 3 K)Assembly halls 3±6 1.0±2.0Bedrooms 1±2 0.33±0.66Boiler rooms and engine rooms 10±15 3.33±5.0Class rooms 3±4 1.0±1.33Corridors 2±3 0.67±1.0Entrance halls 3±4 1.0±1.33Factories, large open type 1±4 0.33±1.33Factories, densely occupied workrooms 6±8 2.0±2.67Foundries, with exhaust plant 8±10 2.67±3.33Foundries, without exhaust plant 10±20 3.33±6.67Hospital operating rooms 20 6.67Hospital treatment rooms 10 3.33Kitchens above ground 20±30 6.67±10.0Kitchens belowground 40±80 13.33±26.67Laboratories 10±15 3.33±5.0Laundries, dye houses and spinning mills 10±20 3.33±6.67Libraries 3±4 1.0±1.33Living rooms 1±2 0.33±0.67Offices above ground 2±6 0.67±2.0Offices belowground 10±20 3.33±6.67Restaurants and canteens 10±15 3.33±5.0Rolling mills 8±10 2.67±3.33Stores and warehouses 1±2 0.33±0.67Workshops with unhealthy fumes 20±30 6.67±10.0