To prevent instances of flash crashes on stock exchanges, the Securities and Exchange Board of India, SEBI, has come out with stringent norms that require bourses to ensure that brokers implementappropriate risk checks before executing a trade.The measures, unveiled yesterday, come more than two months after a massive 900-point flash-crash of the benchmark stock index Nifty, wiped out nearly 10 lakh crore rupees of investor wealth. Sebi has directed stock exchanges not to execute orders exceeding 10 crore rupees in the normal market.In addition, exchanges have to ensure that appropriate checks for value are implemented by the stock brokers based on the respective risk profile of their clients. All the measures are to be implemented within one month of the issuance of circular.