From decades I have been reading that, fire services would spray foam on the runway, in order to avoid fire, on a belly landing. Is this procedure still being used? If not, what would be the safest procedure?
Firefighting services still apply foam path, atleast outside US, though the practice is no longer encouraged.
FAA, in its 2002 CertAlert 02-04 actively discourages it:
The FAA does not recommend the foaming of runways for emergency landings and warns against the practice with any foam other than “Protein” foam.... It is recommended that ARFF personnel decline to foam a runway when requested by a pilot because they do not have the specialized equipment and protein foam
FAA lists a number of reasons for this decision (It had actually recommended foam paths for emergency landings in 1966, before withdrawing it in 1987), including,
Time may not be always available for foaming
The use of foam in foam path should not affect the subsequent firefighting abilities.
Foaming the runway should not affect the movement and safety of other aircraft.
ICAO too, does not recommend for foaming the runway in its Airport Services Manual, stating,
15.1.2 The effectiveness of runway foaming is not fully substantiated by the real evidence of operational incident studies.
ICAO also considers the various reasons for foaming the runway and analyses them:
a) Reduction in aircraft damage. ... The data available from a study of emergency landings made with, and without, the application of foam show that no significant reduction is achieved in the risk of fire or in the extent of damage by the foaming of runways.
Reduction in deceleration forces. ... It is to be noted that from what is known to date, the braking action of an aircraft on a foamed runway will only be slightly worse than that on a wet runway, assuming non-freezing weather.
Reduction in friction spark hazard. ... tests have shown that aluminium alloy metals produce no friction sparks capable of igniting aircraft fuel vapours ... on either dry or foam-covered concrete or asphalt runway surfaces. ... Titanium friction sparks, capable of igniting aircraft fuel vapours, could not be effectively suppressed by runway foaming in any of the scale research tests ...
Reduction in fuel spill fire hazard. From all that is known of the fire suppression qualities of foam and the scale research tests, it is clear that a foamed runway would have no appreciable effect on the fire hazard of fuel vapours in the atmosphere over the foam.
ICAO also points out that the primary firefighting vehicles should not be used for foam laying operations; Also, the time taken for the operations and replenishment is a concern.
It is to be noted that, though the practice is no longer recommended, fire services are not barred from using it if the pilot asks for it and facilities are available.
In a related note, US armed forces seem to use it.