I refer to:
Sundaram and Subramanian 2005, Indian Institute of Astrophysics:
http://adsabs.harvard.edu/abs/2005MNRAS.359..580S
The Authors discuss the properties of isolated type I bursts.
Abstract: "Type I noise storms constitute a sizeable fraction of the active Solar radio emission component. Observations of isolated instances of such bursts, in the swept-frequency mode at metric wavelengths, have remained sparse, with several unfilled regions in the frequency coverage. Dynamic spectra of the burst radiation in the 30-130MHz band, obtained from the recently commissioned digital High Resolution Spectrograph at the Gauribidanur Radio Observatory, have unravelled in explicit detail the temporal and spectral profiles of isolated bursts thanks to the instrument's superior frequency and time resolution. Apart from presenting details of their fundamental emission features, the time- and frequency-profile symmetry, with reference to custom-specific Gaussian distributions, has been chosen as the nodal criterion to statistically explain the state of the source regions in the vicinity of magnetic reconnections, the latent excitation agent that contributes to plasma-wave energetics, and the quenching phenomenon that causes damping of the burst emission."
From their Fig. 3 shown below, the duration of type I isolated bursts is about 1 to 6 seconds at 40 MHz.
http://adsabs.harvard.edu/abs/2005MNRAS.359..580S
The Authors discuss the properties of isolated type I bursts.
Abstract: "Type I noise storms constitute a sizeable fraction of the active Solar radio emission component. Observations of isolated instances of such bursts, in the swept-frequency mode at metric wavelengths, have remained sparse, with several unfilled regions in the frequency coverage. Dynamic spectra of the burst radiation in the 30-130MHz band, obtained from the recently commissioned digital High Resolution Spectrograph at the Gauribidanur Radio Observatory, have unravelled in explicit detail the temporal and spectral profiles of isolated bursts thanks to the instrument's superior frequency and time resolution. Apart from presenting details of their fundamental emission features, the time- and frequency-profile symmetry, with reference to custom-specific Gaussian distributions, has been chosen as the nodal criterion to statistically explain the state of the source regions in the vicinity of magnetic reconnections, the latent excitation agent that contributes to plasma-wave energetics, and the quenching phenomenon that causes damping of the burst emission."
From their Fig. 3 shown below, the duration of type I isolated bursts is about 1 to 6 seconds at 40 MHz.