Dear Rajesh,
As explained by Mr.R.K.Nair, the doctrine of notional extension of employment is a principle developed by the higher judiciary in order to expand the scope of the application of the EC Act,1923 to employment accidents resulting in death or permanent total or partial disability of the employee in respect of time or place of employment.
In fact, this doctrine revolves around the reasonably expanded nexus between the cause of the accident and the employment in respect of the time or place of the accident or both. Thus under certain circumstances, the causal connection between the accident and the employment can be notio ally extended with reference to the time or place of the accident. In other words, the time or place of the accident or both should be so proximate to the hours or nature of employment or both so as to give a wider interpretation to the term ' work' as generally understood.
The opposite of this principle is " the doctrine of added peril " founded by the Judiciary in order to release the employer from the liability of paying compensation under certain circumstances. Here, more importance is given to the place of accident whether the employee by his presence in such a place exposes himself to the risk like any other member of the public.
To understand better, you should go through the texts of judgments by different High Courts and the Supreme Court of India.