Ventilation Check on a Kitchen Range
You are called to a flat to service a gas hob and oven. The kitchen is 3.2 m long, 2.8 m wide, and 2.4 m high. It has a 2.1 m² window that opens, but the customer keeps it closed in winter. The hob is a 4-burner model with a total rated heat input of 10.5 kW. The oven is a separate 3.0 kW appliance. There is a 150 mm diameter extractor fan in the ceiling, but it is not interlocked with the gas supply. The customer reports that the hob flames sometimes go out when the kitchen door is closed and the extractor is running. The kitchen door has a 10 mm gap at the bottom. The flat has a gas boiler in a separate cupboard, which has its own ventilation. You must assess whether the kitchen ventilation is adequate for the installed appliances and whether the extractor fan poses a risk.
1. Calculate the minimum required ventilation for the kitchen appliances and compare it with the existing provisions. Show your reasoning.
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First, determine the total heat input of the appliances in the kitchen: hob 10.5 kW + oven 3.0 kW = 13.5 kW. For appliances in a room, the ventilation requirement is based on the total heat input. For a room with an opening window, the requirement is 5 cm² per kW of heat input for the first 7 kW, plus 2.5 cm² per kW for the remainder. However, for kitchens, the requirement is often 5 cm² per kW for all kW if the room is a kitchen, but check the standards. Actually, for a kitchen, the requirement is 5 cm² per kW for the first 7 kW and 2.5 cm² per kW thereafter, but with a minimum of 35 cm². Wait, the standard for kitchens is 5 cm² per kW for all appliances, but let's use the general formula. For heat input > 7 kW, free area = (7 × 5) + ((13.5 - 7) × 2.5) = 35 + 16.25 = 51.25 cm². But for kitchens, the requirement is 5 cm² per kW for the first 7 kW and 2.5 cm² per kW for the rest, but with a minimum of 35 cm². So required = 51.25 cm². However, if the room has an opening window, the permanent ventilation requirement may be reduced. But since the window is kept closed, we must consider permanent ventilation. The existing window is not permanent ventilation. The door gap: 10 mm × door width (assume 800 mm) = 80 cm², but door gaps are not considered permanent ventilation unless they are purpose-provided and not easily blocked. The extractor fan: 150 mm diameter gives an area of π × (75 mm)² = 17671 mm² = 176.7 cm², but it is not permanent ventilation; it is mechanical extract. The kitchen has no purpose-provided permanent ventilation. Therefore, the ventilation is inadequate. Also, the extractor fan can cause negative pressure, leading to spillage of combustion products. The flames going out indicate that the extractor is pulling air from the room and possibly affecting the appliance. The door gap may not be sufficient to supply the extractor (typical extractor rate 150-300 m³/h). So the answer: required permanent ventilation = 51.25 cm², but none provided; the window is not permanent; the door gap is not reliable; the extractor fan is a hazard. Recommend installing permanent ventilation of at least 51.25 cm² (e.g., a 100 cm² air brick) and interlocking the extractor with the gas supply or ensuring adequate make-up air.
2. What are the potential risks of the extractor fan running while the appliances are in use, and what actions should you take?
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The extractor fan can create negative pressure in the kitchen, especially when the door is closed. This can cause combustion products to spill from the appliances into the room instead of going up the flue (if the appliances are flued) or can cause incomplete combustion due to lack of oxygen. The flames going out suggest that the extractor is affecting the flame stability, possibly due to downdraught or oxygen depletion. The fan is not interlocked, so it can be operated independently. The risks include carbon monoxide poisoning and fire. You should test the appliances with the extractor running and the door closed to see if spillage occurs (using a smoke match or CO detector). If spillage is detected, the appliances must be classified as Immediately Dangerous (ID) and disconnected. Even if not immediately dangerous, the lack of ventilation and the extractor fan are At Risk (AR). You should advise the customer to keep the window open when using the appliances and the extractor, and recommend installing an interlock or additional ventilation. You should also check that the fan does not exceed the make-up air capacity. Document your findings and issue a warning notice.