The strikes are being held in protest at Government reforms to pensions and started on Friday with firefighters not reporting for duty between midday and 1700.
Two further walk-outs will be held on Saturday, 3 May (1400-0200) and Sunday, 4 May (1000-1500).
Private contractors will provide a “basic” level of fire cover during the strikes but Londoners are being urged to “take extra care” to avoid fires starting.
Fire Brigade bosses say the bank holiday weekend is likely to see Londoners dusting off their barbecues and warn they could be at risk if they don’t use common sense.
Fire Commissioner Ron Dobson said: “Barbecues are fine as long as you take a few sensible steps, such as lighting them well away from anything that could catch fire and never leaving them unattended. It’s important to take care with gas barbecues too as gas can explode when exposed to heat.
“During the FBU’s strikes we will have a contingency fire and rescue service of 27 fire engines, crewed by temporary firefighters.
“We will still attend emergencies but the contingency service is not intended to match the Brigade’s normal day to day cover so it is important that people take extra care with their barbecues, have working smoke alarms in their home and take fire safety seriously.”
